Antenatal Screening 
for Down Syndrome 
and Other Conditions  
Guidelines for health practitioners

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Antenatal and newborn screening
The National Screening Unit (NSU) of the Ministry of Health is responsible for the 
development, implementation and management of three antenatal and newborn 
screening programmes:
 
>  Universal Offer Antenatal HIV Screening Programme
 
>  Newborn Metabolic Screening Programme
 
>  Universal Newborn Hearing Screening and Early Intervention Programme.
The NSU is also responsible for the introduction of quality improvements to antenatal 
screening for Down syndrome and other conditions.
Quality improvements to antenatal screening for Down syndrome and other conditions 
have been introduced to bring this screening in New Zealand into line with international 
best practice. While all pregnant women are advised about this screening, it is optional. It 
is made available so that those women who wish to have this information about their baby 
are able to find out during their pregnancy and plan accordingly.
These guidelines replace the Guidelines for maternity providers offering antenatal 
screening for Down syndrome and other conditions in New Zealand dated November 2009.
Acknowledgements
The National Screening Unit would like to thank the many individuals and groups who 
contributed to the development of these guidelines.
National Screening Unit. 2012. Antenatal Screening for Down Syndrome  
and Other Conditions: Guidelines for health practitioners. 
Wellington: Ministry of Health 
 
Published in February 2013 
by the Ministry of Health 
PO Box 5013, Wellington 6145, New Zealand
ISBN 978-0-478-37338-7 (print) 
ISBN 978-0-478-37341-7 (online) 
HP 5409
This document is available on the National Screening Unit website: 
www.nsu.govt.nz

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Contents
Antenatal and newborn screening 
ii
Acknowledgements ii
Key messages 
v
1. Introduction 
1
2. Background 
2
2.1  Overview of antenatal screening for Down syndrome and other conditions 
2
2.2 The screening options 
2
2.3 Screening performance 
4
2.4  Potential benefits and harms of antenatal screening for Down syndrome and other conditions 
4
3. General requirements 
5
3.1  Code of Health and Disability Services Consumers’ Rights 
5
3.2 Health Information Privacy Code 
5
3.3 Ensuring services meet the needs of women 
5
4. The screening pathway 
7
5. Documentation 
9
6.  Informed choice – consent or decline 
10
6.1 Initial discussion 
16
7. The screening tests 
17
7.1  Timing of first trimester combined OR second trimester maternal screening tests 
17
7.2 Ordering tests 
18
7.3 Completing the screening request form 
18
8.  Receiving and communicating results 
21
9. Diagnostic testing 
27
10.  Genetic services and other referrals 
31
11.  Nuchal Translucency (NT) scan 
33
12.  Screening laboratory processes 
38
13.  Data, information and monitoring 
41
13.1 Data and information collection 
41
13.2 Uses of data and information 
42
13.3 Monitoring 
42
Appendix 1:  Resources and contacts 
43
Appendix 2:  Screened conditions 
47
Appendix 3:  Robinson equation 
55
Glossary of terms 
56
Antenatal screening for Down syndrome and other conditions: Guidelines for health practitioners iii

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Key messages
 
1.   Antenatal screening for Down syndrome and other conditions provides a risk estimate 
for Down syndrome (trisomy 21), trisomy 18 (Edwards syndrome), trisomy 13 (Patau 
syndrome) and some other rare genetic disorders.  Page 2
2.   Detection of fetal anomalies through this screening offers women information that may 
help them prepare for the birth of their child: the option of delivery in a setting that has 
access to specialist surgical or medical care; the possibility of considering termination; 
or palliative care in the newborn period.  Page 2
3.   Antenatal screening for Down syndrome and other conditions is optional for pregnant 
women.  Page 10
4.   The right to decline screening, decline tests or further investigations should be made 
clear by the health professional and any such decision by the woman, including 
withdrawal of consent, must be respected.  Page 10
5.   Women who are less than 20 weeks pregnant must be advised about the availability of 
antenatal screening for Down syndrome and other conditions.  Page 10
6.   Up-to-date information about antenatal screening for Down syndrome and other 
conditions must be provided to support the screening discussion, thus enabling women 
to make an informed decision whether to accept or decline.  Page 10
7.   Informed choice for this screening must include a discussion about the screened 
conditions and the decisions that may need to be made as a result of participation in 
this screening.   Page 10
8.   No single test checks for everything. No screening test finds all cases of a condition.  
Page 10
9.   A thorough family history should be taken and where there is a family history of a 
genetic condition, a referral for a discussion with a specialist obstetrician or genetic 
services should be offered prior to screening.  Page 15
10. First trimester combined screening should be completed between 9 weeks and 13 weeks 
6 days gestation. The recommended timing for the blood test is 9 to 10 weeks and 
for the Nuchal Translucency scan is at 12 weeks.  Page 17
11.  Second trimester maternal serum screening should be completed between 14 weeks and  
20 weeks gestation. The recommended timing for this test is 14 to 18 weeks.  Page 17
12. A very high or very low level of the blood markers used in screening may indicate other 
conditions such as pre-eclampsia or pre-term birth. Fetal anomalies such as a heart 
condition or structural defect may be found on ultrasound.  Page 21
13. Screening for neural tube defects (NTD) can be reported after 15 weeks of pregnancy 
using alpha fetoprotein (AFP) as the serum marker. It is noted that a better predictor of 
NTD is the 18 to 20 week anatomy scan.  Page 21
14. The health professional requesting screening must fill in all sections of the screening 
request form to ensure an accurate risk assessment.  Page 18
15. Clear documentation of the screening process must be kept in the clinical records 
including the discussion, consent or decline of tests or referrals and results of 
screening.  Page 9
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
v

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List of abbreviations
AFP Alpha-fetoprotein 
ASUM 
Australasian Society for Ultrasound in Medicine 
ßhCG 
Beta-human chorionic gonadatrophin 
BPD 
Biparietal diameter 
CRL 
Crown–rump length 
CVS 
Chorionic villus sampling 
DHB 
District Health Board 
EDD 
Estimated date of delivery 
FMF 
Fetal Medicine Foundation 
IVF 
In vitro fertilisation 
LMC 
Lead maternity carer 
LMP 
Last menstrual period 
MoM 
Multiple of the median 
NSU 
National Screening Unit of the Ministry of Health 
NTD 
Neural tube defect 
NT 
Nuchal translucency 
NZDSA 
New Zealand Down Syndrome Association 
PAPP-A 
Pregnancy-associated plasma protein A 
RANZCOG   Royal Australian and New Zealand College of Obstetricians and Gynaecologists
RANZCR 
Royal Australian and New Zealand College of Radiologists 
uE  
Unconjugated oestriol
3
vi Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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1.   Introduction
These guidelines support health practitioners advising about the availability of services 
for antenatal screening for Down syndrome and other conditions. They are intended for 
all practitioners involved in aspects of antenatal screening for Down syndrome and other 
conditions including:
 
>  lead maternity carers (LMCs)
 
>  midwives
 
>  general  practitioners
 
>  nurses
 
>  sonologists, sonographers, radiologists
 
>  obstetricians, fetal medicine specialists
 
>  screening laboratory staff.
Health practitioners advising women about maternity care have an obligation under the 
Primary Maternity Services Notice 2007, issued pursuant to section 88 of the New Zealand 
Public Health and Disability Act 2000, to advise women of screening services available that 
are endorsed by the Ministry of Health, including antenatal screening for Down syndrome 
and other conditions.
During the screening process, the health practitioner is responsible for:
(a) providing information and education about antenatal screening to pregnant women
(b) supporting women to make an informed decision
(c) offering referrals as agreed with the woman
(d) communicating screening results
(e) ensuring documentation of screening discussions and choices in the clinical notes
(f) ensuring compliance with the:
 
>  Privacy Act 1993 and Health Information Privacy Code 1994
 
> New Zealand Public Health and Disability Act 2000
 
>  Code of Health and Disability Services Consumers’ Rights 1996
 
> Health Act 1956
 
>  Health Practitioners Competence Assurance Act 2003
 
>  Public Records Act 2005
 
>  Crimes Act 1961 (as amended).
It is strongly recommended that health practitioners complete the e-learning modules 
at www.learnonline.health.nz which have been approved as professional development 
by the Midwifery Council of New Zealand and the Royal Australasian College of General 
Practitioners (RNZGP).
Other screening resources are available for health practitioners at www.nsu.govt.nz
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
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2. Background
Antenatal screening for Down syndrome and other conditions has been available to 
pregnant women in New Zealand since 1968. In October 2007, the government agreed to 
implement quality improvements to antenatal screening for Down syndrome and other 
conditions to ensure consistency with international best practice. The objective of the 
quality improvements initiative is to ensure that the screening tests available for pregnant 
women in New Zealand provide the best possible information, so that women can make an 
informed decision about the way their pregnancy is managed.
2.1   Overview of antenatal screening for Down 
syndrome and other conditions
Detection of fetal anomalies through this screening offers women information that 
may help them prepare for the birth of their child: the option of delivery in a setting 
that has access to specialist surgical or medical care; the possibility of considering 
termination; or palliative care in the newborn period.
Antenatal screening for Down syndrome and other conditions is a way of assessing the 
probability that a baby has Down syndrome or another genetic condition and offers women 
information and choice in the care and management of their pregnancy and baby’s birth.
Antenatal screening for Down syndrome and other conditions has complex ethical  
and social implications. In addition there are technical considerations which involve a  
trade-off between the sensitivity (detection rate) and the specificity (false positive rate)  
of the screening tests. The combination of ultrasound and maternal serum markers 
increases detection rates (improves sensitivity) and/or reduces the number of women 
considered to be at increased risk (improves specificity), compared with previous first 
trimester screening practice.
These guidelines refer to the risk estimate calculations and reports. Health practitioners 
are encouraged to use different methods for communicating individual risk results to 
women and this may include words such as chance or likelihood. The use of risk in these 
guidelines is synonymous with chance used in the consumer information.
2.2  The screening options
Antenatal screening for Down syndrome and other conditions provides a risk 
estimate for Down syndrome (trisomy 21), trisomy 18 (Edwards syndrome),  
trisomy 13 (Patau syndrome) and some other rare genetic disorders.
This screening divides women into two groups based on risk, either increased risk or low 
risk. Table 1 outlines the screening options.
First trimester combined screening involves a nuchal translucency (NT) scan and 
maternal serum testing. The risk is calculated by the screening laboratory from the NT 
measurement, the serum marker levels and other factors including crown-rump length, 
maternal age and weight. Women will receive one combined result from their health 
practitioner, after they have had both the blood test and the NT scan. The incorporation of 
serum results in the risk calculation significantly increases the sensitivity and specificity 
of screening and provides a better risk assessment than NT scanning in isolation1.
1.  Wald NJ, Rodeck C, Hackshaw AK, Walters J, Chitty L, Mackinson AM. 2003. First and second trimester 
antenatal screening for Down’s syndrome: the results of the Serum, Urine and Ultrasound Screening Study 
(SURUSS). Health Technol Assess 7(11): 1-77.
2
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Second trimester screening involves maternal serum testing only. The results of the serum 
tests are incorporated with other parameters such as maternal age, weight and gestation to 
provide a risk report.
The option of screening during the second trimester means screening can be offered to 
women who:
 
>  do not access maternity care early in their pregnancy
 
>  do not have access to NT scanning for geographic, economic or other reasons
 
>  have not completed first trimester combined screening
 
> prefer second trimester screening.
Table 1: The screening options available
First trimester  
Second trimester  
Recommendations 
combined screening  
OR maternal serum screening  AND for practice 
(9 – 13w and 6 days)
(14 – 20 weeks)
 
>  Blood test that 
 
>  Blood test that 
 
> The discontinuation of 
measures two maternal 
measures four maternal 
the use of maternal age 
serum markers (PAPP-A 
serum markers (ßhCG, 
and nuchal translucency 
and ßhCG) combined 
AFP, uE  and inhibin A).
as screening tools in 
3
with an ultrasound scan 
 
>  Available to women 
isolation.
to determine NT and CRL 
who present after the 
measurements.
first trimester or who do 
 
>  Available to all women 
not access first trimester 
who present in the first 
combined screening.
trimester.
 
>  The blood test is fully 
 
>  The blood test is fully 
funded.
funded.
 
> Women may be required 
to make a co-payment 
for the ultrasound scan.  
(The Ministry of Health 
funds the ultrasound 
provider on a fee for 
service basis for each  
NT scan).
Provision of accurate, balanced information (both medical and non-medical).
Support for decisions made by women throughout pregnancy, including the decision as to 
whether or not to participate in screening.
Support for women who want their family/whãnau to be actively involved.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
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2.3  Screening performance
The screening test relies on accurate and full information being provided by the health 
practitioner. The screening request form must include details of gestation, IVF, weight, 
smoking status, ethnicity and relevant family history.
In New Zealand, the screening cut-off is 1:300. As an example, a woman with a risk result  
of 1:250 will be increased risk and 1:350 will be low risk.
Based on international data, this screening finds approximately 85% of babies with Down 
syndrome. Approximately 5% of women will receive an increased risk result.
2.4   Potential benefits and harms of antenatal 
screening for Down syndrome and other 
conditions
All pregnant women must be advised about the availability of antenatal screening 
for Down syndrome and other conditions, including the risks, benefits and harms of 
screening, so that they may make an informed decision to participate in screening or 
not. Screening poses different ethical considerations from those that arise when a person 
presents for medical care because they are unwell. Health practitioners have a special duty 
of care when advising women of screening.
The potential benefits of antenatal screening for Down syndrome and other conditions 
include:
 
>  access to information that may provide more choice in the care and management of  
the pregnancy and birth
 
>  reassurance associated with low risk results for the screened conditions
 
>  reassurance associated with no abnormalities found through scanning.
The potential harms of antenatal screening for Down syndrome and other conditions 
include:
 
>  anxiety and stress associated with the screening process
 
>  women having a poor understanding of the screening process. This may include a lack of 
understanding of risk estimates and what may or may not be detected
 
>  anxiety and stress associated with an increased risk result which may be a false  
positive result
 
>  false reassurance when a low risk result is given when the baby does have a condition  
ie, a false negative result
 
> a miscarriage resulting from diagnostic procedures following an increased risk result.
4
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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3.  General requirements
3.1   Code of Health and Disability Services 
Consumers’ Rights
The Code of Health and Disability Services Consumers’ Rights provides that New Zealand 
health care consumers have a legal right to appropriate information to enable informed 
consent. Information about the Code can be obtained from the Health and Disability 
Commissioner’s website, www.hdc.org.nz
3.2  Health Information Privacy Code
The Health Information Privacy Code 1994 (HIPC) sets specific rules for agencies in 
the health sector to ensure the protection of individual privacy. It addresses health 
information collected, used, held and disclosed by health agencies.
For the health sector, the HIPC takes the place of the information privacy principles set out 
in the Privacy Act 1993. The HIPC can be viewed at the Privacy Commissioner’s website, 
www.privacy.org.nz
The 12 rules of the HIPC require agencies to be clear about the purpose for which they 
collect information, and open about those purposes to the health consumers they collect 
it from. Health information must be held securely to protect it against misuse, loss or 
unauthorised disclosure.
Health consumers can access their health information (with some minor exceptions) and 
seek its correction when it is wrong. Health information should only be used or disclosed 
for the purposes for which it was collected, unless one of the exceptions in the HIPC 
applies.
3.3  Ensuring services meet the needs of women
Health services should be tailored to meet the needs of the individuals receiving them. 
This helps to ensure equity of access and outcomes. Health services should enable people 
to take responsibility for managing their own health.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
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Achieving Equitable Outcomes
Guidelines
Information
Health services should be attuned to 
Health services should be tailored to meet the 
the needs of individuals, families and 
health needs of all New Zealanders, including 
communities. 
Mãori, Pacific peoples and Asian populations.
 
Health practitioners should recognise that 
 
what works for different populations varies.
 
Health practitioners should familiarise 
themselves with Whãnau Ora found at  
www.health.govt.nz and the NZ Disability 
Strategy found at www.odi.govt.nz
Health practitioners should offer additional 
Appropriate information that allows for 
support to women who have difficulty 
informed consent includes using professional 
understanding information because of 
interpreter services, such as Language Line, 
language difficulties, hearing impairment or 
a DHB interpreter or a NZ Sign Language 
intellectual disability. 
interpreter where necessary. Using family 
 
members or friends as interpreters is not 
 
recommended practice.
 
Women who have an intellectual disability  
 
may require extra support or the presence  
of family/whãnau or other support people  
 
(eg independent advocate, welfare guardian) 
 
to understand the information and assist their 
decision making.
Health practitioners should recognise other 
Barriers to accessing aspects of antenatal care 
barriers to access.
and screening may include lack of knowledge, 
fear of health services, different cultural views 
of health, the location and cost of ultrasound 
services, the availability of transport, travel 
time and child care.
6
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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4.  The screening pathway
Figure 1 details the screening pathway. It is the woman’s choice whether to accept 
screening or not and she may also accept or decline any referral or test.
The points along the pathway where the woman needs to make an informed decision are:
(a) whether or not to be screened
(b) whether to accept an offer of referral to a specialist obstetrician or specialist medical 
maternity service or Genetic Services to gather more information following an 
increased risk or abnormal result
(c) whether to have diagnostic testing following a referral and discussion
(d) when deciding the next step after receiving the results of the diagnostic test.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
7

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Figure 1: The screening pathway
Antenatal screening for Down syndrome and other conditions
Provision of information 
Initial discussion 
Offer of screening
about screening
First visit
End of screening 
Screening declined
Screening accepted
process
Sc
reenin
g
First trimester combined  
Second trimester combined  
screening accepted
screening accepted
• Less than 13 Weeks 6 Days Pregnant 
• 14–20 Weeks Pregnant 
OR
• Blood test (2 maternal serum markers) 
• Blood test (4 maternal serum markers)
• NT scan
Laboratory algorithm 
generates risk report
Results to health 
practitioner
Low risk result 
Increased risk 
received
result received
Offer of specialist referral 
following increased risk result
Continue with 
management 
of pregnancy
Specialist referral 
Specialist referral 
Di
declined
accepted
agno
stic
Offer of diagnostic 
testing
Offer of diagnostic 
Offer of diagnostic 
testing declined
testing accepted
No condition 
Condition identified. 
identified
Referral as appropriate
8
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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5. Documentation
Clear documentation of the screening process must be kept in the clinical records 
including the discussion, consent or decline of tests or referrals and results of 
screening.
Details of discussions and decisions must be documented by the health practitioner in 
the clinical records. Signed consent for antenatal screening for Down syndrome and 
other conditions is not required by the Code of Health and Disability Services Consumers’ 
Rights.
Clinical Records
Guidelines
Information
Health practitioners must document 
Each stage of the screening process should be 
discussions and decisions in the clinical 
documented in the clinical records including:
notes. 
 
>  the content of discussions with the woman
 
 
>  the use of interpreters or other services
 
 
 
>  consent or decline for screening and 
procedures or further testing
 
>  details of results, follow up or referral
 
>  discussions with the woman on results 
 
received
 
 
>  other support, resources or information 
 
offered or provided.
 
Health practitioners who are referring 
Referral information should include:
or handing over care to another health 
 
>  consent or decline for screening
practitioner must provide appropriate 
 
>  details of screening tests ordered
documentation.
 
>  results of screening
 
>  any follow-up from screening results
 
>  any relevant family history
 
>  referrals made to other services.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
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6.   Informed choice –  
consent or decline
Women who are less than 20 weeks pregnant must be advised about the availability 
of antenatal screening for Down syndrome and other conditions.
Antenatal screening for Down syndrome and other conditions is optional for 
pregnant women.
The right to decline screening, decline tests or further investigations should be made 
clear by the health professional and any such decision by the woman, including 
withdrawal of consent, must be respected.
Informed choice for this screening must include a discussion about the screened 
conditions and the decisions that may need to be made as a result of participation  
in this screening.
Up-to-date information about antenatal screening for Down syndrome and other 
conditions must be provided to support the screening offer, thus enabling women  
to make an informed decision whether to accept or decline.
No single test checks for everything. No screening test finds all cases of a condition.
Ensuring women make an informed decision about antenatal screening for Down 
syndrome and other conditions is a legal requirement under the Code of Health and 
Disability Services Consumers’ Rights that is central to best practice in maternity care.
Participation in antenatal screening for Down syndrome and other conditions is entirely 
the woman’s choice. The woman also has the option to accept or decline further testing or 
referrals within the screening pathway. For instance, a woman may decline first trimester 
combined screening, but later change her mind and accept second trimester screening. All 
choices that the woman makes must be respected and supported by health practitioners 
providing her care.
10 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Information to Women
Guidelines
Information
Health practitioners must advise women about 
The discussion of screening must be made 
the availability of antenatal screening for 
with sufficient information, advice and time to 
Down syndrome and other conditions which 
enable women to make an informed decision.
is available to all pregnant women under 20 
The discussion with women should be initiated 
weeks gestation.
by the health practitioner as early as possible 
in the pregnancy, to allow the opportunity to 
ask questions, seek further information and 
consider participation.
Women should be informed that only one 
screening option will be publicly funded in 
each pregnancy. Only one risk result will be 
issued.
Women should be informed that screening 
provides a risk estimate and not a definitive 
result.
Some women may wish to discuss their  
options with family/whãnau.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners
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Informed Consent or Decline
Guidelines
Information
Health practitioners must provide up-to-date,  
Information should include the Ministry  
balanced information about the screened 
of Health consumer pamphlet Antenatal 
conditions.
screening for Down syndrome and other 
conditions: optional screening – your choice, 
Health practitioners must ensure women are 
your decision.
aware this screening is optional.
Discussion about screening should include 
Health practitioners must respect and support 
that there may be unexpected findings. Refer 
all screening choices the woman makes.
to Appendix 2 for more details.
Informed consent is a process that must occur 
throughout the screening pathway. 
Ensuring informed choice includes:
 
> provision of information about screening
 
>  offering screening in a non-directive manner
 
>  discussions about screening before and 
during the screening process
 
>  discussions about options following an 
increased risk screening result
 
>  giving sufficient time to consider options
 
>  documenting discussions and consent or 
decline to screening
 
>  assuring the woman that whatever choice 
she makes will be supported.
Communication
Guidelines
Information
Health practitioners must answer questions 
Women should be given the opportunity to ask 
women ask regarding screening.
questions about this screening and advised 
where they can find further information.
Health practitioners may need to seek advice 
from other sources to assist them to answer 
questions from women for example from 
screening laboratories, radiology practices, 
obstetricians, paediatricians, Genetic Services 
and/or maternal fetal medicine specialists.
12 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Communication continued
Guidelines
Information
Health practitioners should give women time 
Health practitioners should be cognisant of the 
to reflect and consider decisions.
important implications for pregnant women 
when screening is discussed.
Where there is a history of pregnancy problems 
and/or genetic conditions in the family, 
women may have given careful thought to how 
they want to proceed with this pregnancy.
A woman’s decision whether or not to consent 
to screening will depend on her personal 
values and beliefs and the information 
available to her.
Women will have a range of different views 
that may change over time. Some women are 
very clear what choices they may make if a 
condition is confirmed and others are not.
This screening (and the implications of 
screening) involves complex ethical issues 
and women may want to explore these before 
giving consent to begin screening or to 
continue screening.
For some women, screening is an opportunity 
to have information that enables them to 
choose the care and management of their 
pregnancy and birth. Screening and diagnostic 
testing can inform the choice of location for the 
birth, for instance a tertiary unit with specialist 
care.
Women may wish to consider the choices 
following an increased risk result. This may 
include a discussion about:
 
> diagnostic testing including the risks
 
>  what a positive diagnostic result may mean 
for her.
If a woman does not wish to know further 
information about the pregnancy then she may 
choose not to have screening.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 13

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Screened Conditions
Guidelines
Information
Health practitioners must discuss the 
Conditions include:
conditions that may be indicated as a result  
 
>  risk estimates for trisomy conditions:
of participation in this screening.
 
>  T21 (Down syndrome)
 
>  T18 (Edwards syndrome)
 
>  T13 (Patau syndrome)
 
>  other rare genetic conditions for example:
 
>  Smith-Lemli-Opitz
 
>  Turner  syndrome
 
>  Triploidy
All the conditions above will require diagnostic 
testing for confirmation.
Pregnancy conditions associated with poor 
placentation including:
 
>  stillbirth
 
>  miscarriage
 
>  growth  restriction
 
>  preterm  birth
 
>  pre-eclampsia.
The ultrasound scan may show structural 
anomalies for instance:
 
>  cardiac
 
>  neural  tube
 
>  renal
 
>  central nervous system.
The ultrasound scan may also suggest  
a growth anomaly.
The conditions above require referral as 
appropriate.
As with any medical test, there is a chance 
that other conditions may be unexpectedly 
identified and a recommendation for further 
discussion with a specialist may be made.
Screening is not able to detect all conditions 
that may be present.
The results will provide a risk estimate for T21, 
T18 and T13 as well as incidental findings. 
Further advice can be obtained from the 
laboratory if required.
14 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Screened Conditions continued
Guidelines
Information
Health practitioners must discuss with the 
The 18 to 20 week anatomy scan is not 
woman that the 18 to 20 week anatomy scan is 
included in this screening, however, it may 
another screening test.
identify potential markers for one of the 
screened conditions.
A thorough family history should be taken and where there is a family history of a 
genetic condition, a referral for a discussion with a specialist obstetrician or genetic 
service should be offered prior to screening.
Family History
Guidelines
Information
Health practitioners must discuss and 
If a woman has previously been pregnant with 
document family history with the woman and 
or has had a child with a genetic condition, 
advise the laboratory of any relevant details.
or a family history of a genetic condition, they 
may have a different risk status.
Appropriate family history questions (on both 
sides of the family) may include:
 
>  previous recurrent miscarriage
 
>  previous pregnancy loss (still birth or 
neonatal death)
 
>  fetal or childhood abnormalities (for example 
neural tube defects)
 
>  developmental delay in other children
 
>  any genetic conditions including childhood 
diseases, cystic fibrosis, muscular dystrophy 
or neurodegenerative conditions.
The practitioner may wish to consult with 
Genetic Services prior to determining a 
management plan.
It may be appropriate that the woman is 
offered a referral to a specialist obstetrician or 
specialist medical maternity service or Genetic 
Services.
Health practitioners should exercise particular 
sensitivity and be aware that women may have 
already given careful thought to having or not 
having screening or diagnostic testing.
A referral form for Genetic Services is available at www.nsu.govt.nz
Genetic Services
Phone Number
Northern and Midland Region
0800 476 123
Central and Southern Region
0508 364 436
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 15

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6.1  Initial discussion
The discussion should include the following information.
(a) Screening information
 
>  purpose of screening
 
>  screening options available and what screening involves
 
>  screened  conditions
 
>  detection of structural anomalies on the NT scan
 
>  screening does not cover every condition
 
>  incidental information may be found relating to the pregnancy or baby
 
>  recommended timing for screening
 
>  screening pathway and the decision points and options for screening
 
>  screening provides a risk estimate only and is not diagnostic
 
>  a further test would be required to determine whether a condition is present
 
>  reliability of screening
 >  which tests may incur charges
 >  further information about the baby may be identified at the 18 to 20 week anatomy scan.
(b) Resources
 
>  the consumer resource, Antenatal screening for Down syndrome and other conditions: 
Optional screening – your choice – your decision should be given at this time.
(c) Consent
 
>  screening is optional and a woman may choose to participate or not participate in first 
or second trimester screening and change her mind about this decision 
 
>  the woman may choose to participate in second trimester screening having declined 
the offer of first trimester combined screening
 
>  women who choose not to participate in screening will not have their maternity care 
affected in any way
 
>  if screening shows an increased risk result, diagnostic testing will be offered.
(d) Results
 
>  how results are notified
 
>  women will receive one risk result for first trimester combined screening combining 
NT scan measurements and serum markers
 
>  when screening results are available
 
>  the screening will provide an increased or low risk result and may also indicate other 
anomalies through ultrasound or serum markers
 
>  for every 1000 women screened, about 50 will receive an increased risk result and 2 
will be diagnosed with a baby with Down syndrome or another condition
 
>  woman’s preference for receiving her results.
(e) Data and information collection and monitoring
 
>  information and data is collected and securely stored
 
>  information is used for monitoring and quality improvements of this screening
 
>  that this screening is monitored at a national level including monitoring and 
evaluating pregnancy and birth outcomes
 
>  Monitoring reports or any public information will present summary information only 
and will not be identifiable.
16 Antenatal screening for Down syndrome and other conditions: Guidelines for health practitioners

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7.  The screening tests
7.1   Timing of first trimester combined OR 
second trimester maternal screening tests
First trimester combined screening should be completed between 9 weeks and  
13 weeks 6 days gestation. THE RECOMMENDED TIMING FOR THE BLOOD TEST IS  
9 TO 10 WEEKS AND FOR THE NT SCAN AT 12 WEEKS.
Second trimester maternal serum screening should be completed between  
14 weeks and 20 weeks gestation. THE RECOMMENDED TIMING FOR THIS TEST IS  
14 TO 18 WEEKS.
Figure 2 shows when the different antenatal screening tests for Down syndrome and other 
conditions may be undertaken.
Figure 2:  Timing of first trimester combined screening and second trimester serum 
screening
First trimester combined screening
Second trimester maternal serum screening
9 weeks to 13 weeks 6 days
14 weeks to 20 weeks
9W
10W
11W 12W
13W
6D 14W
15W
16W
17W
18W
19W
20W
Recommended 
Recommended timing for 
timing for
maternal serum markers 
 maternal 
14 – 18 weeks
serum 
markers 
9 – 10 weeks
Recommended 
timing for NT scan 
12 weeks
Antenatal screening for Down syndrome and other conditions: Guidelines for health practitioners
17

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7.2  Ordering tests
If a woman accepts screening, the health practitioner (midwife or doctor) will complete the 
screening request form.
Eligibility criteria for publicly funded services can be found at www.moh.govt.nz
First Trimester Screening
Guidelines
Information
Health practitioners should inform women 
For first trimester combined screening, health 
where they can go for their blood test and NT 
practitioners must ensure the woman knows 
scan and the timing of each of these tests for 
there are two components, blood test and 
first trimester combined screening.
ultrasound scan, and she needs to have each 
within certain timeframes.
Referrals for the NT ultrasound must be made 
in accordance with Section 88 of the New 
The woman is usually required to make a  
Zealand Public Health and Disability Act 2000.
co-payment for the NT scan.
Second Trimester Screening
Guidelines
Information
Health practitioners should inform women 
Second trimester serum screening is fully 
where they can go for the blood test and 
funded for eligible women.
the timing of the test for second trimester 
screening.
7.3  Completing the screening request form
The health professional requesting screening must fill in all sections of the screening 
request form to ensure an accurate risk assessment.
Screening Request Form
Guidelines
Information
The screening request form must be completed 
All information requested on the laboratory 
with all the requested information.
request form is needed by the laboratory to 
ensure high quality testing. Screening results 
may be inaccurate if the information on the 
screening request form is not completed.
The current screening request form is a carbon copy, with the duplicate copy to be used for 
NT scan requests. Figure 3 provides further explanation.
From time to time, the screening request form format may change, however, the 
information required for accurate risk assessment will stay the same.
18 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Two laboratories perform antenatal screening for Down syndrome and other conditions. 
LabPLUS (Auckland District Health Board) are responsible for screening women from 
Taupo north. Canterbury Health Laboratories (Canterbury District Health Board) are 
responsible for screening women south of Taupo.
Laboratory contact details for enquiries and screening request form orders:
Laboratory
Phone Number
LabPLUS
0800 LABPLUS (0800 522 7587)
Canterbury Health Laboratories
0800 THE LAB ( 0800 843 522)
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 19

---

Figure 3: The screening request form
i
a
gg
h
b
f
c
d
e
 
a Multiple pregnancies: serum analyte levels come from the baby and placenta so will differ for multiple pregnancies.
 
b Smoking: affects placental function and serum analyte levels. The default if not provided is a non-smoker.
  Weight: smaller women have higher serum analyte levels and larger women have lower serum analyte levels. This has a significant 
c impact on the risk calculation.
 
d Diabetes: serum analyte levels differ for diabetic women.
  Gestation and IVF: levels of serum analytes change through the pregnancy, so dating is important for accurate risk calculation. 
e Essential information includes accurate gestation details including the method and age of the woman at the time of donation/
retrieval.
  Previous pregnancy details: these are added into the risk calculation as they affect the chance of the current pregnancy. Add any 
f relevant family history.
 
g Mother’s ethnicity: serum analyte levels vary with different ethnicities.
  NT scan expected date and site: this relates to which practice the woman is most likely to go to for her NT scan.  
h The laboratory will contact the radiology practice if they have not received an NT scan report by 13 weeks.
 i Patient and health practitioner details: this section ensures the right patient is linked to the right result and sent to the right health 
practitioner. Your phone number ensures you can be contacted to check details or provide results. Please provide alternative details if 
you will be away.
20 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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8.   Receiving  and 
communicating results
A very high or very low level of the blood markers used in screening may indicate 
other conditions such as pre-eclampsia or pre-term birth. Fetal anomalies such as a 
heart condition or structural defect may be found on ultrasound.
Screening for neural tube defects (NTD) can be reported after 15 weeks of pregnancy 
using alpha fetoprotein (AFP) as the serum marker. It is noted that a better predictor 
of NTD is the 18 to 20 week anatomy scan.
Blood samples are generally received by the screening laboratory two to three days after 
collection. Screening results will be completed by the screening laboratory within three 
business days after the receipt of the blood sample or scan information, whichever is 
the later (if first trimester combined screening). Screening results include information 
provided about the woman, details of the risks and recommendations.
The screening laboratory will send a report to the health practitioner if both parts of 
screening (ie, NT scan and blood tests) have not been received by 13 weeks 6 days.
Receiving Screening Results
Guidelines
Information
The health practitioner is responsible for 
It is useful to ascertain the woman’s 
receiving screening results.
preference for receiving results at the time that 
the screening offer is made.
The woman may wish to be accompanied by 
family/whãnau or support person.
If the screening result is low risk the screening 
laboratory will dispatch the result to the health 
practitioner by mail or electronic means within 
24 hours of the result being available.
If the screening result is increased risk the 
screening laboratory will phone the health 
practitioner within 24 hours of the result being 
available. The result will also be dispatched to 
the health practitioner by mail or electronically.
There are a number of situations where the 
markers (both serum and the NT scan) may 
indicate other conditions. Refer to Appendix 2 
for further information.
If the screening result will indicate other 
conditions, the screening laboratory will phone 
the health practitioner within 24 hours of the 
result being available.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 21

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Preparing for Communicating Screening Results
Guidelines
Information
Health practitioners must communicate 
Prior to communicating with the woman, the 
results to women in an appropriate and timely 
health practitioner should consider discussing 
manner.
the result with the screening laboratory or 
Genetic Services.
 
 
Communication to women needs to occur 
 
through reliable methods such as face to face 
 
or telephone, taking into account appropriate 
 
timing (such as the need for timely referral or 
follow up). Results or professional advice must 
not be sent via a text message.
 
 
Consideration should be given to the timing of 
 
giving results and whether access to timely support 
 
services or further information is available (for 
example on public holidays or Friday afternoons).
 
Health practitioners should be able to present 
 
results in a clear and concise way to support 
 
women in their decision-making. This includes 
understanding statistical risk information.
 
It can be useful to communicate the risk result in 
 
different ways to help women better understand 
for example:
 
 
>  ‘You have a 1 in 4 chance of…, or put another 
 
way, you have a 25 percent chance of….’
 
>  ‘You have a 1 in 20 chance of having a baby 
with one of the conditions, this means there is 
 
a 19 in 20 chance of having a baby without the 
 
condition.’
Further information about the risk result can be 
 
obtained from the screening laboratory.
 
The health practitioner should be prepared to 
Discussion around the results may include:
discuss the results in detail and seek further 
 
>  the limitations of screening
information that supports them to inform 
 
>  that a low risk result means that the baby is 
women what their screening results may mean.
unlikely to be born with one of the conditions 
screened for, but it does not mean they will 
definitely not be born with one of the conditions 
(or another condition not indicated by screening)
 
>  providing an opportunity for the woman  
(and her family/whãnau) to ask questions
 
>  providing information about other services, 
including community support agencies the 
woman (and her family/whãnau) can contact.
If a woman with a low risk result requests 
diagnostic testing, a referral to a specialist 
obstetrician may be made.
22 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Communicating Increased Risk Results and Offering Referral
Guidelines
Information
Health practitioners must inform women 
Consideration should be given to the timing 
in a timely manner of all screening results 
of giving results and whether access to timely 
indicating an increased risk of Down syndrome 
support services or further information is 
or another condition.
available (for example, on public holidays or 
Friday afternoons).
Anxiety following any increased risk result is 
normal. Anxiety includes the stress and worry 
experienced while waiting for decisions about 
diagnostic testing, and the possibility of a 
higher level of anxiety for the remainder of  
the pregnancy.
If screening shows an increased risk of 
a genetic condition, women may require 
more information to enable them to make 
an informed decision about the ongoing 
management of their pregnancy; one which 
they feel is best for themselves and their 
families.
Sources of information and support are listed 
in Appendix 1.
Document the discussion and management 
plan in the clinical notes.
Provide the woman with a copy of the results if 
requested.
Figures 4 and 5 provide an example of the screening reports produced by the laboratories.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 23

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Figure 4: Example laboratory report: increased risk for Down syndrome
NHI and demographic 
details of the patient. 
Please check these 
are correct.
Which trimester this 
screening occurred in
The health practitioner 
who ordered the test 
This information is 
(name on the request 
based on what was 
form), and who the 
provided on the 
result will be sent to.
request form. Please 
check these are 
correct.
The cut-off for 
aneuploidy risk is 
This is the results 
1:300. This example 
section. It details 
report shows 1:85 which 
the NT measurement 
is an increased risk for 
and MoMs for each 
Down syndrome.
marker. It then 
details the risk result 
for the aneuploidies. 
Note the ‘increased’ 
next to risk of Down 
syndrome.
This is the summary 
section detailing an 
increased risk (relating 
to the increased risk 
for Down syndrome in 
this example).
If any of the  
woman’s details 
are not correct or  
the LMC has 
any questions, 
please contact 
the laboratory 
(LabPLUS or CHL).
24 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Figure 5: Example laboratory report: low PAPP-A (unusual analyte)
NHI and demographic 
details of the patient. 
Please check these 
are correct.
Which trimester this 
screening occurred in
The health practitioner 
who ordered the test 
(name on the request 
This information is 
form), and who the 
based on what was 
result will be sent to.
provided on the 
request form. Please 
check these are 
correct.
This is the results 
section. It details 
the MoMs for  
each marker.  
In this example,  
an NT has not yet 
This is the summary 
been received.  
section showing the 
The MoM for PAPP-A 
very low PAPP-A result 
is significantly 
and that the NT scan 
reduced. PAPP-A 
has not been received 
MoMs will be 
by the laboratory.
reported as reduced 
if they are less 
than 0.2.
If any of the  
woman’s details 
are not correct or  
the LMC has 
any questions, 
please contact 
the laboratory 
(LabPLUS or CHL).
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 25

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Referral to Specialist
Guidelines
Information
Health practitioners must offer a timely referral 
Following an increased risk result a woman 
to all women with increased risk results or 
may be undecided about her next steps. She 
unusual analytes.
may require further information from other 
sources about:
 
 
 
>  what the increased risk result may mean and 
how it may affect the on-going management 
of the pregnancy and birth
 
 
>  the difference between treatable conditions 
(for instance heart defects) and non-treatable 
 
conditions (for instance trisomy 13).
 
The referral should include details of:
 
 
 
>  gestation
 
>  screening  results
 
>  any issues identified which require further 
discussion
 
 
>  any relevant family history.
 
A referral to Genetic Services may provide the 
opportunity to gather information to make 
 
or confirm a diagnosis of a genetic disorder. 
 
Other referrals may also be considered. These 
 
include:
 
 
 
>  a  paediatrician 
 
> a health social worker
 
>  a  counsellor.
 
The woman may wish to seek further 
 
information from sources listed in Appendix 1.
The woman must be given time to reflect and 
to consider her decision.
Health practitioners must make clear the 
The provision of links to community 
woman’s right to decline a referral following an 
organisations to enable the gathering of more 
increased risk result.
information and to access support may also be 
helpful. These can be found in Appendix 1.
Health practitioners must respect and support 
any decision made by the woman throughout 
the screening process.
26 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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9.  Diagnostic testing
Diagnostic testing includes a procedure to collect a sample of fetal cells either by  
chorionic villus sampling (CVS) or amniocentesis. The sample collected is sent for 
aneuploidy testing.
CVS can be performed from 11 to 14 weeks of pregnancy but is typically performed  
between 10 and 13 weeks. CVS is only offered in a few centres. CVS results may take one  
to three weeks.
Amniocentesis can be performed between 15 and 20 weeks. Amniocentesis results may 
take one to three weeks.
A more detailed scan may be required following an abnormal finding on ultrasound or 
from unusual analytes or positive NTD screen.
Diagnostic testing is publicly funded for women who have:
 
>  an increased risk result
 
>  an abnormal ultrasound scan (structural abnormalities)
 
>  previously had a baby with a congenital anomaly
 
>  maternal  anxiety
 
>  a family history of Down syndrome and/or other conditions, if recommended by Genetic 
Services.
International best practice does not support direct referral to diagnostic testing based on 
maternal age alone.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 27

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Diagnostic Testing
Guidelines
Information
Health practitioners must provide information 
Health practitioners should outline the 
on diagnostic testing and inform the woman 
following choices the woman has available:
that diagnostic testing is optional.
 
>  whether or not to accept a referral and 
diagnostic testing
 
>  referral to another service for example a 
paediatrician, Genetic Services, health social 
worker or counsellor.
The health practitioner must explain:
 
>  what information the diagnostic tests can 
provide
 
> the risks associated with a diagnostic test
 
>  the decisions that the woman  may need  
to consider
 
>  the anxiety that may be experienced while 
waiting for results and possibly for the 
remainder of the pregnancy
 
>  the support services that can be accessed.
Fetal cells can be analysed in a number  
of ways. 
There is an option of more rapid tests which 
can provide a result in 24 to 48 hours. These 
tests are accurate but do not test for as 
many abnormalities as other testing. Further 
information is available from the laboratories. 
A charge may apply for these tests.
If diagnostic testing is undertaken, the sample 
can be used for chromosome testing and 
for other specific genetic tests that may be 
indicated in the family history. These will need 
to be specified on the diagnostic testing form 
sent to the cytogenetics laboratory.
28 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Diagnostic Testing continued
Guidelines
Information
Health practitioners must inform women of the 
The risk of miscarriage after amniocentesis 
risk of diagnostic testing procedures. 
is about one miscarriage in every 100–200 
women tested.
 
The risk of miscarriage after CVS is about one 
miscarriage in every 50–100 women tested. 
Other rare complications include:
 
>  leaking of amniotic fluid from the vagina
 
>  infection of the uterus or fetus
 
>  some research has suggested that 
 
development of arms, fingers, legs or toes 
 
may be disrupted if CVS is performed before 
 
nine weeks gestation: for this reason, a CVS 
 
procedure is done after 10 weeks gestation.
 
>  development of Rhesus factor 
 
incompatibility. All women who have Rh-
 
negative blood group are given an injection 
of anti-D to prevent this complication.
Specialist obstetricians who are performing 
If diagnostic testing is undertaken, the sample 
diagnostic testing must specify the genetic 
can be used for chromosome testing and 
tests required on the diagnostic testing form. 
for other specific genetic tests that may be 
This may include requests due to familial 
indicated in family history. These will need to 
conditions.
be specified on the diagnostic testing form 
sent to the cytogenetic laboratory.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 29

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Receipt of a Positive Result Following Diagnostic Testing 
Guidelines
Information
The health practitioner must explain the 
Health practitioners can seek further 
meaning of any test results and provide 
information from the cytogenetic laboratory  
information about any diagnosis.
or other sources as required.
 
See Appendix 2 for more information on the 
conditions.
 
Women may wish to have time to consider the 
 
results and what they may mean for her and 
her baby.
After receiving the results of the diagnostic 
The following could be discussed:
test, health practitioners should support 
 
>  information about the condition
women to make an informed decision.
 
>  options available which include:
Health practitioners must support the woman’s 
 
>  continuing with the pregnancy
decision.
 
>  termination of the pregnancy.
If the woman chooses to continue with the 
pregnancy, the options for antenatal care such 
as specialist care and support, and postnatal 
options should be discussed. If the baby 
has a condition which has a very short life 
expectancy, consideration should be given to 
offering antenatal or postnatal palliative care 
for the baby and counselling services to the 
 
women (and her family).  
 
Women may need to be provided with support, 
which may include access to groups in 
Appendix 1.
Health practitioners must provide women with 
This may include referral to a:
opportunities to access additional information 
 
>  paediatrician
and support.
 
>  health social worker
 
>  Genetic  Services
 
>  counsellor.
The woman and/or her family/whãnau  
may seek information from sources listed  
in Appendix 1 to find out what living with  
a specific condition may mean.
Written resources for example, Living  
With Down and web links are available  
(see Appendix 1).
30 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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10. Genetic services and  
other referrals
Genetic Services
Guidelines
Information
Health practitioners should advise women with 
Staff from Genetic Services can provide 
increased risk results about the availability of 
information and support for families with,  
Genetic Services.
or at risk of, a genetic disorder.
Referrals to Genetic Services should come  
from the GP or LMC in the first instance. A copy 
of the screening report should be included.
Initial discussions with the health practitioner 
will be conducted with the cover (on call) 
genetic associate.
If the health practitioner wishes a staff 
member (genetic associate or clinical 
geneticist) to subsequently talk to the woman, 
this should be handled as a formal referral.
Please use the Genetic Services Referral  
form available from the NSU website at  
www.nsu.govt.nz/files/ANNB/Referral_form_
final120511.pdf
Genetic Services are physically located in 
Auckland, Wellington, and Christchurch. 
Telephone or in-person consultations will be 
negotiated based on the woman’s location  
and circumstances.
Any queries about the screening laboratory 
analytical process and the result algorithm can 
be referred back to the designated specialists 
in LabPLUS and CHL.
Genetic Services
Phone Number
Northern and Midland Region
0800 476 123
Central and Southern Region
0508 364 436
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 31

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Other Referrals
Guidelines
Information
Health practitioners must provide information 
Health practitioners should find out about 
about medical and non-medical services the 
services in their area and how to access them.
woman may access to support her to make 
Referrals may include:
decisions about the management of her 
pregnancy.
 
>  obstetrician
 
>  specialist maternity services
 
>  maternal fetal medicine specialist
 
>  paediatrician
 
>  general medical practitioner
 
>  health social worker
 
>  counsellor
 
>  disability support services
 
>  parent support groups.
Refer to Appendix 1 for resources and contacts.
32 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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11.   Nuchal  Translucency   
(NT) scan
The NSU supports continual improvement in the quality of this screening initiative. This 
includes working with the health sector to monitor and develop ultrasound screening 
practices. Quality improvements will continue to evolve. This may result in changes in 
delivery of service, monitoring and audit.
If the woman agrees to first trimester combined screening the ultrasound/radiology 
provider would then complete the NT and CRL measurements and send the results to the 
screening laboratory.
Referral for NT Scan
Guidelines
Information
Specialist medical maternity services, 
This requires a written referral, stating the 
including NT scans, may only be provided 
clinical reason, either on the screening request 
to women on written referral from another 
form or radiology request form. 
practitioner (midwife or doctor).
Risk Calculation
Guidelines
Information
The risk calculation will be performed by the 
The two screening laboratories are LabPLUS at 
screening laboratories.
Auckland District Health Board and Canterbury 
Health Laboratories at Canterbury District 
Health Board.
The screening laboratories use a single 
database for risk calculation. This ensures 
consistent risk calculation for all women across 
New Zealand.
Discussions With Women
Guidelines
Information
Ultrasound/radiology providers 
It is expected that practitioners may discuss the findings 
may discuss the scan findings 
of the NT scan with the woman, but will not calculate a risk 
with the woman. However, 
result.
ultrasound/radiology providers 
In all but exceptional circumstances, the risk result will be 
should not provide a risk 
communicated to the woman by the referring practitioner. 
assessment for Down syndrome 
There may be very limited circumstances where the 
and other conditions to the 
radiology/ultrasound provider contacts the screening 
woman based on NT alone (for 
laboratory informing  them of the NT and CRL measurements 
example, 1:300 risk).
and requesting a risk assessment (if serum has already been 
taken). This would generally be on the rare occasion where a 
significant anomaly is found on the ultrasound scan. 
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 33

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Reporting Requirements
Guidelines
Information
The following information from the NT scan 
An NT scan is usually performed between  
must be provided for this screening:
11 weeks 2 days and 13 weeks 6 days.  
 
>  National Health Index (NHI) number
For acceptance for first trimester combined 
screening, at the time the NT scan is 
 
>  demographic information (DOB, name)
performed, the fetus must have a CRL between 
 
>  referrer’s  name
45–84mm.
 
>  date of NT scan
The CRL is used by the laboratory to determine 
 
>  the CRL measurement
gestational age from the Robinson equation 
 
>  the NT measurement
(see Appendix 3).
 
>  multiple pregnancy (chorionicity and 
Precise measurement of CRL and NT is 
amnionicity)
essential in the interpretation and final risk 
 
>  other details that may inform the risk 
assessment provided to the pregnant woman.
calculation
The combined screening test is highly  
 
>  significant abnormalities which may change 
sensitive to errors in CRL measurement and  
the management of the pregnancy
NT measurement.
 
>  name of the practice
The name of the scanning practitioner in 
 
>  name of the radiologist
addition to the reporting radiologist or 
 
>  name of the practitioner performing the scan.
obstetrician on the report will provide audit  
at an individual level.
Best practice report templates can be found  
at www.nsu.govt.nz
Nasal Bone Assessment
Guidelines
Information
Nasal bone will be included in the risk 
Nasal bone assessment is not currently 
calculation if it is reported to the screening 
required to provide a risk result for first 
laboratory at the same time as the NT 
trimester combined screening.
measurement.
When an NT measurement is provided to  
 
the screening laboratory and a risk has  
 
been issued, no further risk calculation will 
 
be done if the nasal bone is assessed at a 
subsequent scan.
Nasal bone is to be reported as:
If a result states that a nasal bone is 
 
>  not looked for
hypoplastic, this will not be included in the 
risk calculation.
 
>  present
 
>  absent
 
>  not able to be visualised for technical 
reasons
34 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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CRL Out of Range for First Trimester Combined Screening
Guidelines
Information
If the CRL is greater than 84mm, the 
For first trimester combined screening, the CRL 
ultrasound/radiology provider is to inform the 
should be between 45 – 84mm. Where the CRL 
woman that the fetus is outside the range for 
is greater than 84mm, the fetus is outside the 
first trimester screening and an NT scan cannot 
range for first trimester combined screening.
be completed. The ultrasound/radiology 
provider will refer the woman back to her 
health practitioner for other options including 
second trimester maternal serum screening.
Specialist Referral Following Abnormal NT
Guidelines
Information
If an NT scan shows an obvious anomaly,  
The referring health practitioner should offer 
for instance structural/anatomical anomaly, 
the woman referral to a specialist obstetrician.
the radiologist should:
(a)   inform the referring health practitioner in  
a timely manner;
(b)  provide information to the woman at the 
time of the scan.
NT Greater Than 3.5 mm
Guidelines
Information
If the NT scan shows a NT measurement greater 
The referring health practitioner should offer 
than or equal to 3.5mm, the ultrasound/
the woman referral to a specialist obstetrician, 
radiology provider should communicate with 
with the expectation she will be seen in a 
the referring health practitioner to discuss the 
timely manner.
scan results.
Completion of first trimester combined 
screening is still recommended. This will assist 
the specialist to develop a care pathway with a 
full clinical picture.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 35

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NT for Twins
Guidelines
Information
For twin pregnancies, an NT and CRL for each 
The screening laboratory uses CRL to date  
fetus must be measured at the same time to 
the pregnancy and hence calculate the marker 
ensure accurate risk assessment.
MoMs. Both NT measurements should be 
made at the time of the CRL measurements.  
If they are different in twins, the larger will  
be used.
Any information that may assist risk calculation 
for each fetus should be included in the report 
to the screening laboratory.
If an NT measurement  is only able to be 
completed on one twin, a subsequent NT scan 
must include NT and CRL for both fetuses  
(if more than 2 days has elapsed).
Transmitting Scan Results to the Screening Laboratories
Guidelines
Information
Ultrasound/radiology providers will transmit 
Ultrasound/radiology providers are to have a 
copies of the report results in a timely 
system in place to send the ultrasound report 
manner direct to LabPLUS for Taupo north or 
to the screening laboratory and to confirm the 
Canterbury Health Laboratories (CHL) for south 
report has been sent.
of Taupo.
Loss of One Twin
Guidelines
Information
For pregnancies where one twin has died, 
If the NT scan identifies a sac showing fetal 
a NT and CRL measurement is to be sent to 
demise, it is possible that there could be a 
the screening laboratory and will be used to 
contribution to the maternal biochemical 
calculate the risk assessment without serum 
markers for many weeks. Therefore, serum 
levels.
analytes are not used to calculate a risk 
assessment. The screening laboratory will 
provide a risk assessment based on NT without 
biochemistry.
NT for Multiple Pregnancies – Triplets or Greater Multiples
Guidelines
Information
For pregnancies with three or more fetuses,  
The screening laboratory software is not able 
an NT alone can be used for risk assessment.
to provide a risk assessment for pregnancies 
where there are triplets or greater multiples.
36 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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The NSU supports International Accreditation New Zealand (IANZ) radiology 
accreditation. This occurs for the majority of practices around New Zealand and provides 
assurance that the practice operates to established standards.
Individual Certification and Standards Requirements
Guidelines
Information
Practitioners must follow the requirements of 
The NSU recommends radiology practices have 
Section 88 of the New Zealand Public Health 
IANZ accreditation. The NSU is developing 
and Disability Act 2000.
initiatives to audit and monitor individual 
operators.
Practitioners should follow the standards of 
practice for diagnostic and interventional 
In New Zealand, the quality of service 
radiology (version 9.1) of the Royal Australian 
requirements relates to appropriate education 
and New Zealand College of Radiologists.
and training for the measurement of NT. 
Appropriate certification is recognised through 
Practitioners should follow the statements  
FMF London and the Australian Nuchal 
from the Royal Australian and New Zealand 
Translucency – Ultrasound, Education and 
College of Obstetricians and Gynaecologists.
Monitoring Program.
Practitioners should follow the requirements  
Further policies and statements on fetal 
of ASUM.
ultrasound can be found at:
www.ranzcog.edu.au
www.ranzcr.edu.au
www.asum.com.au
www.fetalmedicine.com
While ultrasound/radiology providers are no 
longer required to provide the risk calculation 
for women, the requirements of ultrasound 
practitioners providing services remain 
unchanged. This means ongoing participation 
in certification and audit programmes 
continues to be a requirement.
Nasal Bone Certification
Guidelines
Information
Practitioners assessing nasal bone must be 
Nasal bone evaluation requires additional 
certified for the assessment of nasal bone. 
certification over and above that for NT 
assessment. The certification is provided  
by the FMF programme.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 37

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12.  Screening  laboratory 
processes
Reporting Information to the Health Practitioner
Guidelines
Information
The screening laboratory must provide a first 
The screening laboratory report must include:
trimester combined screening or second 
 
> screening result (‘increased risk’ or ‘low risk’)
trimester maternal serum screening result 
 
>  multiple of the median (MoM) of each 
to the health practitioner who referred the 
analyte
woman for screening, by electronic means 
and/or hard copy reporting.
 
>  NT measurement and MoM
 
>  individual risk assessments for:
 
>  trisomy 21 (Down syndrome)
 
>  trisomy 18 (Edwards syndrome)
 
>  trisomy 13 (Patau syndrome)
 
>  neural tube defects (after 15 weeks).
The screening laboratory report may include 
other information, for example that specialist 
obstetric referral is recommended, that a rare 
genetic disorder is indicated or that the marker 
levels indicate other problems.
The screening cut-off is 1:300 for aneuploidies.
Provision of Specialist Laboratory Advice
Guidelines
Information
The screening laboratory must provide 
The screening laboratory will phone all 
specialist laboratory advice to the health 
increased risk results and abnormal analyte 
practitioner, when requested.
results and discuss these with the health 
practitioner.
The screening laboratory must ensure 
that health practitioners have screening 
Health practitioners are welcome to contact 
information required to inform women of their 
the screening laboratory if required.
screening results.
38 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Incomplete Screening
Guidelines
Information
The screening laboratory will provide a report 
The screening laboratory will inform the 
to the health practitioner when a blood sample 
health practitioner if the NT scan has not been 
for first trimester combined screening has 
received.
been received, but no NT or CRL measurement.
The screening laboratory will advise the health 
practitioner to contact the woman about the 
need to have her scan performed before 13 
weeks 6 days for a first trimester combined 
screening risk assessment to be possible.
If the scan has not been performed by 13 
weeks 6 days, the screening laboratory will:
 
>  issue a report to the health practitioner that 
provides the MoMs of the serum analytes only
 
>  advise that first trimester combined 
screening cannot be completed because  
the scan data was not available
 
>  recommend that the woman is offered 
second trimester maternal serum screening.
The health practitioner should advise the 
woman that first trimester combined screening 
has not been completed and provide her with 
information about second trimester maternal 
serum screening.
The screening laboratory will advise the 
The screening laboratory will accept a CRL of 
health practitioner if first trimester combined 
45–84 mm. If the result is above 84mm, the 
screening cannot be completed because the 
screening laboratory will advise the health 
CRL is above 84mm.
practitioner that the woman is in the second 
trimester.
If the blood has also been taken in the second 
trimester, second trimester screening will be 
performed.
If the blood has been taken in the first 
trimester, the health practitioner will be 
informed that first trimester combined 
screening cannot be completed and provide 
her with information about second trimester 
maternity screening.
The screening laboratory will indicate on the 
reports the dating used to calculate the risk. 
Preference will be given to CRL or BPD over LMP.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 39

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Further Serum Received
Guidelines
Information
The screening laboratory will advise the health 
The screening laboratory will advise the health 
practitioner if a serum sample has been 
practitioner that a risk result has already been 
received after a result has already been issued.
provided and a further result will not be issued 
unless there are clinical indications. The 
health practitioner must phone the laboratory 
to discuss as required. Decisions regarding 
recalculating risk assessments will be made on 
a case by case basis.
Laboratory
Contact Details
Contact Details
LabPLUS 
www.labplus.co.nz 
Taupo and North (Northland, 
Phone: 0800 LABPLUS (522 7587)
Waitemata, Counties Manukau, 
Auckland, Waikato, Lakes and  
 
Lead Clinical Scientist: 
Bay of Plenty)
 
Dr Dianne Webster 
[email address]
Canterbury Health 
www.chl.co.nz 
South of Taupo (Tairawhiti, Hawkes 
Laboratories
Phone: 0800 THE LAB  
Bay, Whanganui, Taranaki, Mid 
   
(843 522 x 80484)
Central, Wairarapa, Capital & Coast, 
Hutt Valley, Nelson Marlborough, 
Chemical Pathologist: 
West Coast, Canterbury, South 
Dr Richard MacKay 
Canterbury, Southern)
[email address]
40 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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13.   Data,  information   
and monitoring
13.1  Data and information collection
Antenatal screening for Down syndrome and other conditions collects, creates and retains 
indefinitely the following data and information. Table 2 outlines what information is 
collected.
Table 2:  Data and information collected for antenatal screening for Down syndrome and 
other conditions
Information About the Woman  Sample Data 
Health Practitioner Data 
as Collected on the Request 
 
 
Form
 
>  name (in full)
>   date and time of samples/
>   name
 
>  National Health Index (NHI) 
scans
>  midwifery/medical council 
number
>  collection and screening 
number
 
>  date of birth
laboratory assigned ID#
>   radiology practice and 
 
>  gestation at time of 
>  screening results
practitioner
sampling
>  diagnostic results and 
>  telephone numbers
 
>  ethnicity
outcomes
>  address
 
>  weight
>  information about what 
has been reported and to 
 
>  information about the 
whom including any clinical 
pregnancy
information provided
 
>  estimated date of delivery
 
>  relevant family history
This data and information is held indefinitely by the screening laboratories on behalf of 
the National Screening Unit.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 41

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13.2  Uses of data and information
Only authorised personnel have access to the identifiable information and data for the 
purposes of screening, quality assurance, monitoring and evaluation.
Data and information is collected and held securely to:
 
>  interpret screening results
 
>  make sure that results can be provided to health practitioners
 
>  monitor and evaluate this screening including the results of diagnostic testing and 
outcomes of pregnancies.
Data and information may also be used in research studies.
From time to time, there may be requests for screening data. This may include data requests 
for research or other requests from individuals, committees, groups or organisations. 
Any requests regarding this data must be forwarded to, and authorised by, the National 
Screening Unit. The data access request form can be found at www.nsu.govt.nz
Data Requests
Guidelines
Information
All requests for screening data must be 
To maintain consistency, all screening data 
forwarded to, and authorised by, the National 
requests will be managed by the National 
Screening Unit.
Screening Unit. This includes data requests for 
research, or from other individuals, committees, 
groups or organisations.
 
13.3 Monitoring
Antenatal screening for Down syndrome and other conditions is overseen by the National 
Screening Unit of the Ministry of Health. To maintain the quality of this screening, it is 
closely monitored on a regular basis, with evaluation undertaken periodically. Monitoring 
is dependent on the information collected as set out in Table 2 which includes the 
numbers of screened women, practitioner information, results and outcomes (for instance 
comparing screening results with diagnostic results or pregnancy outcomes).
The Ministry of Health publishes reports on this screening. These reports are summary 
information only and do not contain identifiable data or information.
42 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Appendix 1:  
Resources and contacts
Sources of further information and contact details for support services are listed here.  
This list should be supplemented by the local or regional services within your own networks.
The National Screening Unit (NSU), of the Ministry of Health is responsible for oversight 
of antenatal screening for Down syndrome and other conditions. The NSU produces 
consumer and practitioner resources and audits and monitors this screening initiative.
The consumer resource Antenatal screening for Down syndrome and other conditions: 
optional screening – your choice, your decision can be downloaded in pdf form at www.nsu.
govt.nz Hard copies are available free of charge and can be ordered at www.healthed.govt.
nz or by contacting the Authorised Provider of Health Education Resources in your area.  
A full list of who these are (by region) is at www.healthed.govt.nz/contact-us
These practitioner guidelines can be downloaded from www.nsu.govt.nz Hard copies 
are available from Wickliffe on (04) 496 2277, Ministry of Health Publications, c/- Wickliffe 
Press, PO Box 932, Dunedin, or email [email address] Please quote Code: HP5409.
On-line education for health practitioners who provide services within the antenatal  
and newborn screening programmes can be accessed at www.learnonline.health.nz
Consumer Questions and Answers and other support information can be found at  
www.nsu.govt.nz
For questions or comments: [email address]
Mailing address: 
National Screening Unit 
Private Bag 92522 
Wellesley Street 
Auckland
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 43

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There are two Screening Laboratories. LabPLUS at Auckland District Health Board and 
Canterbury Health Laboratories at Canterbury District Health Board.
Laboratory request forms can be ordered from the Screening Laboratories.
Laboratory
Contact Details
Contact Details
LabPLUS 
www.labplus.co.nz 
Taupo and North (Northland, 
Phone: 0800 LABPLUS (522 7587)
Waitemata, Counties Manukau, 
Auckland, Waikato, Lakes and  
 
Lead Clinical Scientist: 
Bay of Plenty)
 
Dr Dianne Webster 
[email address]
Canterbury Health 
www.chl.co.nz 
South of Taupo (Tairawhiti, Hawkes 
Laboratories
Phone: 0800 THE LAB  
Bay, Whanganui, Taranaki, Mid 
   
(843 522 x 80484)
Central, Wairarapa, Capital & Coast, 
Hutt Valley, Nelson Marlborough, 
Chemical Pathologist: 
West Coast, Canterbury, South 
Dr Richard MacKay 
Canterbury, Southern)
[email address]
NZ Maternal Fetal Medicine Network 
www.nzmfm.health.nz
Genetic Services, New Zealand 
Northern and Midland Region 
Phone: 0800 476 123
Central and Southern Region 
Phone: 0508 364 436 
www.genetichealthservice.org.nz
Health and Disability Commissioner 
www.hdc.org.nz/
Office of the Privacy Commissioner 
www.privacy.org.nz
Ministry of Health 
Primary Maternity Services Notice 2007 
www.health.govt.nz
Other resources
New Zealand
Auckland District Health Board 
Management of Babies with Down syndrome 
www.adhb.govt.nz/newborn/Guidelines/Anomalies/DownSyndrome.htm
ASUM 
www.asum.com.au
College of Midwives 
www.midwife.org.nz
44 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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CCS Disability Action 
www.ccs.org.nz 
Phone: 0800 227 200
IHC 
www.ihc.org.nz 
Phone: (04) 472 2247
Kiwi Families 
Links to disability support articles 
www.kiwifamilies.co.nz
Midwifery Council of New Zealand 
www.midwiferycouncil.health.nz
New Zealand Down Syndrome Association 
www.nzdsa.org.nz 
Tel. 0800 693 724 
Email: [email address]
New Zealand Federation of Disability Information Centres 
www.nzfdic.org.nz
New Zealand Organisation for Rare Disorders 
www.nzord.org.nz
Pacific Information Advocacy Support Services 
www.vakatautau.co.nz
Parent and Family Resource Centre 
www.parentandfamily.org.nz
Parent to Parent 
www.parent2parent.org.nz
People First 
www.peoplefirst.org.nz/Home/tabid/36/Default.aspx
Prenatal screening tests for trisomy 21 (Down syndrome), trisomy 18 (Edwards 
syndrome) and neural tube defects 
www.ranzcog.edu.au/publications/statements/C-obs4.pdf
Royal Australian and New Zealand College of Obstetricians and Gynaecologists 
www.ranzcog.edu.au
Royal New Zealand College of General Practitioners 
www.rnzcgp.org.nz
Royal Australian and New Zealand College of Radiologists 
www.ranzcr.edu.au
Sands New Zealand 
www.sands.org.nz
Spina Bifida Association of New Zealand
What Everyone Keeps Asking 
www.weka.net.nz
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 45

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Australia
Australian Centre for Genetics Education 
Changes to Chromosomes – Number, Size and Structure Fact sheet 
www.genetics.com.au/pdf/factsheets/fs06.pdf
Mosaicism – Complex Patterns of Inheritance Fact Sheet 
www.genetics.edu.au/pdf/factsheets/fs13.pdf
Down syndrome Fact Sheet 
www.genetics.com.au/pdf/factsheets/fs28.pdf
Trisomy 13 – Patau Syndrome 
www.genetics.edu.au/factsheet/fs29
Trisomy 18 – Edwards Syndrome 
www.genetics.edu.au/pdf/factsheets/fs30.pdf
Human Genetic Society of Australasia (HGSA) 
www.hgsa.com.au
United Kingdom
Antenatal Results and Choices (UK) 
www.arc-uk.org/
Down’s Syndrome Association (UK) 
A New Parent’s Guide 
www.downs-syndrome.org.uk
Down syndrome online 
www.down-syndrome.org
Fetal Medicine Foundation, London 
www.fetalmedicine.com/FMF
The 11–13+6 Weeks Scan 
www.studiolift.com/fetal/site/FMF-English.pdf
International Mosaic Down Syndrome Association 
Booklet for professionals 
www.imdsa.org/Information/professional.htm
National Health Service (UK) 
Antenatal Screening: Introduction 
www.nhs.uk/conditions/Antenatal-screening/Pages/Introduction.aspx
Brief descriptions of other trisomies (13 Patau; 18 Edwards), monosomy (Turner) and also 
Klinefelters, XXX, YY and features which might identify them antenatally 
www.perinatal.nhs.uk/car/anomaly/chromosome/chromosome.htm
National Screening Committee (UK) 
Fetal Anomaly Screening Programme – Screening for Down’s Syndrome: UK NSC Policy 
recommendations 2007–2010: Model of Best Practice 
www.dh.gov.uk/en/Publicationsandstatistics/Publications/
PublicationsPolicyAndGuidance/ DH_084732
46 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Appendix 2:  
Screened conditions
The list of ‘other conditions’ cannot be exhaustive as it is unknown what the ‘condition’ for 
a particular woman or her baby may be. This is the same for blood tests taken in any health 
setting where unanticipated findings may be identified.
The following provides details of the aneuploidies and unusual analytes.
Trisomy 21
Trisomy 21, also known as Down syndrome is a genetic disorder caused by an extra 
copy of chromosome 21 inside each of the body’s cells. The chromosomes are located 
in the nucleus of each cell, and contain the genetic material that, in combination with 
environmental influences, determines a person’s individual characteristics. In Down 
syndrome, instead of a pair there are three copies of chromosome 21. The extra genetic 
material from the extra chromosome results in the physical and intellectual attributes 
which are the characteristics of Down syndrome.
The average life expectancy of people with Down syndrome has increased with improved 
healthcare, better education, greater opportunities and a shift in societal attitudes during 
the past 20 to 30 years. Studies indicate that average life expectancy in the UK was 
estimated to be 9 years of age in 1929 and 12 years in 1949. Subsequent reports have shown 
a marked increase in life expectancy that began in the 1950s. By the year 2000 the median 
life expectancy for people with Down syndrome in Australia was 60 years2.
Recent research shows that parents appreciate information about the abilities and 
potential of people with Down syndrome (eg participation in community sports, activities, 
inclusion in mainstream education classes, employment, independent living, life 
expectancy to 50–60s and having friends); as well as clinical details3. Balancing clinical 
information (eg cause, recurrence risk for future pregnancies, physical features, associated 
medical conditions, intellectual disability and developmental delay) with a better 
understanding of the information parents consider most important, may enable health 
practitioners to provide the information that satisfies the needs of families about Down 
syndrome.
The New Zealand Down Syndrome Association note that:
   ‘People with Down syndrome are all unique individuals and vary 
in their abilities and achievements. They do have features in 
common, but they also closely resemble their parents and family. 
Many characteristics are associated with Down syndrome, but any 
one person will only have some of them. Thus each person is an 
individual, with a unique appearance, personality and set of abilities. 
The extent to which a child shows the physical characteristics of the 
syndrome is no indication of his or her abilities and achievements’4.
2.  Bittles AH, Glasson EJ. 2004. Clinical, social and ethical implications of changing life expectancy in Down 
syndrome. Dev.Med.Ch.Neurol. 46(4): 282-6.
3. Sheets KB, Best RG, Brasington CK, Will MC. 2011. Balanced information about Down syndrome: What is 
essential? Am J Med Genet Part A 155: 1246–1257.
4. www.nzdsa.org.nz (accessed 9 September 2009).
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 47

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Similarly, the organisation Upside of Down report that:
   ‘Today people with Down syndrome live at home with their families 
and are active participants in the educational, vocational, social 
and recreational activities of the community. They are integrated 
into the regular education system, and take part in sports, camping, 
music, art programs and all the other activities of their communities. 
In addition, they are socializing with people with and without 
disabilities, and as adults are obtaining employment and living in 
group homes and other independent housing arrangements’5.
 
People with Down syndrome experience varying degrees of delay in their learning and 
development, and may have additional health needs. They will almost always learn to 
walk, speak, read and write but commonly require support in using money, negotiating 
public transport and building skills for appropriate social behaviour.
Some of the health issues associated with Down syndrome include:
 
>  hearing loss in up to 50 percent of people with Down syndrome
 
>  congenital heart disease in up to 50 percent
 
>  thyroid disorders, most commonly hypothyroidism, in up to 40 percent
 
>  gastrointestinal tract congenital malformations, such as duodenal atresia  
and Hirschsprung’s disease
 
>  cataracts and visual refractive errors
 
>  childhood leukaemia in about 2 percent
 
>  early onset Alzheimer’s disease.
Children with mosiac or partial forms of this trisomy are likely to be less severely affected.
Trisomy 18
Trisomy 18, also known as Edwards syndrome is a chromosomal condition caused by the 
presence of all or part of an extra 18th chromosome.
The syndrome appears to affect females more frequently than males by a ratio of 
approximately three or four to one. Large population surveys indicate that it occurs 
in about one in 5,000 to 7,000 live births6. The incidence increases as the mother’s 
age increases. The syndrome has a very low rate of survival, resulting from heart 
abnormalities, kidney malformations, and other internal organ disorders.
About 50 percent of live born infants with trisomy 18 live to 2 months, and 5–10 percent 
survive their first year of life. Major causes of death include apnea and heart abnormalities. 
It is impossible to predict the exact prognosis of a child with Edwards syndrome during 
pregnancy or post birth. The median lifespan is 5–15 days. A small percentage of babies 
with the full Edwards syndrome who survive birth and early infancy may live to adulthood. 
Children with mosaic or partial forms of this trisomy may have a different morbidity 
and mortality statistics. In mosaic forms there are some cells in the body where the 
chromosome number and structure is different from other cells.
5. www.upsideofdown.org/about_t21 (accessed 13 May 2012).
6. www.rarediseases.org/rare-disease-information/rare-diseases/byID/217/viewFullReport (accessed 13 May 2012).
48 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Trisomy 13
Trisomy 13, also known as Patau syndrome, is a rare chromosomal condition, in which 
there is an additional chromosome 13. The extra chromosome 13 disrupts the normal 
course of development. It causes severe neurological, heart and kidney defects which 
make it difficult for infants to survive. Newborns with trisomy 13 share common physical 
characteristics including: extra fingers or toes (polydactyly), small head (microcephaly), 
facial defects such as small eyes (microphthalmia), absent or malformed nose, cleft lip 
and/or cleft palate.
Many infants have difficulty surviving the first few days or weeks due to severe 
neurological problems or complex heart defects. Surgery may be necessary to repair heart 
defects or cleft lip and cleft palate. Physical, occupational, and speech therapy will help 
those individuals with trisomy 13 who live beyond the first few weeks/months.
Triploidy
Triploidy means that a baby has three copies of each chromosome in each cell rather 
than two, making a total of 69 chromosomes rather than 46. The majority (more than 99 
percent) of babies with triploidy will miscarry or be stillborn. Of those babies born alive, 
most are likely to die in the hours or days following birth. A few babies with triploidy have 
lived five months or longer, but this is rare and usually the babies who survive longer have 
mosaic triploidy rather than full triploidy. Babies with triploidy usually have multiple 
genetic problems  and severe growth restriction.
Neural tube defects
Neural tube defects (NTDs) are birth defects of the brain and spinal cord. The two most 
common neural tube defects are spina bifida and anencephaly. In spina bifida, the baby’s 
spinal column does not close completely during the first month of pregnancy. There is 
usually nerve damage that causes at least some paralysis of the legs. In anencephaly, much 
of the brain does not develop. Babies with anencephaly are likely to be stillborn or will die 
shortly after birth.
Adequate maternal intake of folate/folic acid (400 micrograms per day) commencing 
antenatally and continued through the first trimester of pregnancy significantly reduces 
the probability of  NTD.
First trimester combined screening cannot estimate the risk for NTDs. Second trimester 
screening performed after 15 weeks includes alpha fetoprotein (AFP) which may indicate 
a risk of NTDs at this time. However, more severe forms may be detected at the nuchal 
translucency ultrasound.
For NTDs, including spina bifida, the 18 to 20 week anatomy scan is the best available 
screening tool. The use of AFP as a screening tool for NTDs is neither very sensitive nor 
specific and is not considered best practice internationally and should not be ordered 
specifically with the intention of screening for NTDs.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 49

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Conditions identified by ultrasound
Ultrasound scans undertaken as part of this screening may detect some major fetal 
structural anomalies, such as skeletal anomalies, brain and neural tube defects, congenital 
heart defects, and abnormalities of the renal tract, gastrointestinal system and abdominal 
wall. These will be mentioned in the ultrasound scan report.
An increased NT measurement is associated with trisomy 21, Turner syndrome and other 
chromosomal defects as well as other fetal malformations and genetic conditions.
There are instances where babies have increased NT measurements but at diagnostic 
testing have normal chromosomes. These babies may have an increased risk of a number 
of abnormalities. Conditions associated with increased NT measurement include: 
cardiac malformation, diaphragmatic hernia, omphalocoele, body stalk anomaly, skeletal 
anomalies, Noonan syndrome, Smith-Lemli-Opitz syndrome and spinal muscular 
dystrophy.
Unusual analytes
First trimester combined screening looks at two markers, pregnancy-associated plasma 
protein A (PAPP-A) and Beta-Human Chorionic Gonadatrophin (ßhCG).
Second trimester maternal serum looks at four markers, Alpha-fetoprotein (AFP), Beta-
Human Chorionic Gonadatrophin (ßhCG), Unconjugated Oestriol (uE ) and Inhibin A.
3
The markers used in screening come from the fetus and the placenta. Very abnormal levels 
may indicate a possibility of poor placentation or fetal growth restriction.
For example, if PAPP-A is reduced and/or inhibin-A and/or ßhCG is elevated it has  
been shown that there is a possibility of conditions related to poor placentation such as  
pre-eclampsia , preterm birth or intrauterine growth restriction.
All information identified through screening will be included in the risk report to the 
health practitioner.
Table 3 indicates the analytes measured. It is noted that there may be combinations of 
these markers that indicate increased pregnancy concerns, for instance low PAPP-A and 
low ßhCG or high ßhCG and high AFP.
The correlation of low levels of one or two markers with adverse pregnancy outcomes 
may not be strong, however very low level results can provide information which may be 
combined with ongoing assessment to assist with pregnancy management.
50 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Table 3: Analytes measured during first or second trimester serum testing
What is Measured 
When is it 
Where Does it 
Other Information 
Measured
Come From
Pregnancy 
1st trimester
Produced by 
Very low levels of PAPP-A in the 
associated plasma 
the baby and 
mother’s blood can indicate poor 
 
protein-A (PAPP-A)
placenta
placentation.
 
Beta human 
1st and 2nd 
Produced by the 
High levels of ßhCG in the mother’s 
chorionic 
trimester
baby
blood can indicate problems with 
gonadotrophin 
the pregnancy (for instance fetal 
 
 
(ßhCG)
growth restriction).
 
 
Unconjugated 
2nd trimester
Produced by the 
Very low levels of uE  can indicate 
3
oestriol (uE )
placenta
the biochemical disorders Smith 
3
 
Lemli Optiz syndrome and steroid 
 
 
 
sulphatase deficiency.
 
 
 
Alpha fetoprotein 
2nd trimester
Produced by the 
Very high levels of AFP in the 
(AFP)
baby
absence of structural anomalies 
 
can indicate problems with the 
 
 
 
pregnancy (for instance fetal 
 
 
 
growth restriction).
 
 
 
Inhibin A
2nd trimester
Produced by the 
Very high levels of Inhibin-A can 
placenta
indicate poor placentation.
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 51

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Multiple of the median (MoM)
Serum marker levels used in antenatal screening change by gestational age. Therefore, for 
accurate interpretation of the test results, a different reference range must be used for each 
week of gestation, depending on when the test is drawn. To avoid the multiple reference 
range problems and also to standardize test results a median value for test results in 
normal pregnancies is determined for each week of gestation. The woman’s individual 
analyte levels are compared with the median for that analyte at the appropriate gestational 
age, and expressed as a multiple. This is the multiple of the median. The multiple of the 
median is used as a standard reporting tool for antenatal screening. 
Figure 6 shows that an analyte level of 5 may be increased or decreased depending on 
the stage of pregnancy. At 10 weeks, the median value is 2.5, hence a level of 5 is 2 MoMs 
(elevated) but at 14 weeks, the median value is 10 hence a level of 5 is 0.5 MoMs (decreased).
Figure 6: Serum marker levels by gestational age
10
MoM = 2
MoM = 1
5
MoM = 0.5
 (iu/mL)
el
ev
2.5
er l
ark
Serum m
1.5
10
11
12
13
14
Gestation (weeks)
median serum marker level
tested serum marker level sample
MoM = Multiple of the median
52 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Table 4 show the analyte relationship with aneuploidy. These are not absolute. Most will 
have these patterns but not all.
Table 4: First and second trimester analytes and the relationship with aneuploidy
First Trimester
PAPP-A
Free ßHCG
NT measurement
Trisomy 21
Trisomy 18
Trisomy 13
Second Trimester
Free ßHCG
uE
AFP
inhibin-A
3
Trisomy 21
Trisomy 18
Trisomy 13
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 53

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Impact of accurate information
High quality screening results rely on complete and accurate information which informs 
the risk calculation. This includes details of smoking status, ethnicity, weight, IVF, twins 
and gestational age.
As an example, obesity dilutes the analytes measured, and IVF pregnancies have a higher 
ßHCG. The risk calculation takes these factors into account when they are provided.
The table below provides some scenarios which affect the risk calculation and therefore 
the risk result.
Table 5: Effect of different scenarios on pregnancy risk results
Scenario 
Result 1 
Change in 
Result 2 
Comment 
Details
Change in 
Gestational age 
Ultrasound 
Revised risk 
The analytes 
gestational age 
calculated at 
scan calculated 
calculation 
change over the 
 
15.1 
gestational age 
 
pregnancy and 
 
 
at 14.1 
 
therefore the 
 
 
 
 
risk calculation 
 
 
 
 
changes 
 
T21 risk result: 
 
T21 risk result: 
depending on the 
1:220
1:910
gestational age.
Change from 
Assumed 
Ultrasound scan 
Revised risk 
The analytes are 
singleton to  
singleton 
shows twins
calculation
divided when 
twin pregnancy
pregnancy
there is more 
 
 
than one fetus.
 
T21 risk result: 
 
T21 risk result: 
1:250
1:500
 
Non-smoker  
Assumed  
Health 
Revised risk 
Smoking affects 
to smoker 
non-smoker 
practitioner 
calculation 
placental 
 
 
informs the 
 
function and 
 
 
Screening 
 
inhibin levels 
 
 
Laboratory that 
 
are higher in 
 
T21 risk result: 
the woman is a 
T21 risk result: 
women who 
1:210
smoker
1:300
smoke.
Compounding 
42 year old 
Woman’s age 
Revised risk 
There is a 
effect of many 
woman using 
incorrect – 
calculation 
compounding 
changes
LMP dating at 
found she is 32 
 
effect when 
18,2. No scan 
years of age, 
 
many of the 
data, singleton 
LMP was wrong 
 
variables are 
pregnancy 
and it is actually 
 
incorrect.
reported, 
14,1. Twins, 
 
no weight, 
Smoker and 
 
no smoking 
weighs 45 kg
 
information
T21 risk result: 
T21 risk result: 
1:520
1:13,000
54 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Appendix 3:  
Robinson Equation
The table below outlines the Robinson equation that is used by the screening laboratories 
to measure gestational age. Ranges for NT acceptance are highlighted in the darker cells.
Table 6: The Robinson equation for measuring gestational age
CRL
GA
CRL
GA
in mm
weeks
days
in mm
weeks
days
5
7
1
54.5
12
0
10
7
5
56.5
12
1
15
8
2
58.5
12
2
20
8
6
60
12
3
25
9
2
62
12
4
28
9
4
64
12
5
30
9
5
66
12
6
35
10
0
68
13
0
35
10
2
70
13
1
40
10
5
72
13
2
41
10
6
74
13
3
42
10
6
76
13
4
43
11
0
79
13
5
45
11
0
81
13
6
45.5
11
1
82.6
14
0
46
11
2
83
14
0
48
11
3
84
14
0
49.5
11
4
85
14
1
51
11
5
86
not 
available
53
11
6
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 55

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Glossary of terms
Alpha-fetoprotein (AFP) − a protein that is normally produced by the fetus. Maternal 
serum AFP levels can be used as a biochemical marker in the detection of certain fetal 
abnormalities including NTDs after 15 weeks of pregnancy.
Amniocentesis − a procedure involving the withdrawal of a small amount of amniotic 
fluid by needle and syringe through the abdomen guided by ultrasound performed at the 
same time. The tests performed on fetal cells found in the sample can detect a range of 
chromosomal and genetic disorders.
Analyte − a substance that is undergoing analysis or being measured. Analytes measured 
in antenatal screening include: pregnancy associated plasma protein-A, beta human 
chorionic gonadotrophin, unconjugated oestriol, alpha fetoprotein and inhibin A.
Aneuploidy – is the condition of having less than or more than the normal diploid number 
of chromosomes. For instance, Down syndrome has 47 (not 46) chromosomes with an 
extra chromosome 21.
Beta-human chorionic gonadotropin (ßhCG) − a hormone produced during pregnancy 
and present in maternal blood and urine. It is used as a biochemical marker for Down 
syndrome and other conditions in first trimester combined and second trimester maternal 
serum screening.
Biparietal Diameter (BPD) – the measurement of the distance between the fetal parietal 
bones at their widest point. This is used for dating in the second trimester.
Chorionic villus sampling (CVS) – a procedure involving the withdrawal of a small 
amount of placental tissue by needle and syringe through the abdomen guided by 
ultrasound performed at the same time. Tests performed on the placental cells can detect  
a range of chromosomal and genetic disorders.
Crown rump length (CRL) − the measurement from the fetal crown to the prominence  
of the buttocks or breech. This is used for dating in the first trimester.
Chromosome − an organised structure of DNA and protein found in all living cells that 
carries the genes determining heredity.
Cut-off point − The point that divides people into a group at lower risk or increased risk 
for the condition being screened for. In New Zealand the cut-off point in screening for 
Down syndrome and other conditions is 1:300 at term.
False negative result − when a woman receives a low risk screening result but the baby 
does have the condition screened for.
False positive result − when a woman receives an increased risk screening result but the 
baby does not have the condition screened for.
Inhibin A − a hormone secreted by the ovary that is used as a biochemical marker in 
second trimester maternal serum screening for Down syndrome and other conditions.
Mosaic – the presence of two populations of cells with different genotypes in one patient, 
where usually one of the two is affected by a genetic disorder.
56 Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners

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Multiple of the median (MoM) − a measure which compares the values of a biochemical 
marker in an individual sample with the median value of that biochemical marker in other 
women at the same gestation.
Neural tube defect (NTD) − a congenital anomaly involving the brain and spinal cord 
caused by failure of the neural tube to close properly during embryonic development. 
Open NTDs occur when the brain and/or spinal cord are exposed at birth through a defect 
in the skull or vertebrae. Examples of open NTDs are spina bifida (myelomeningocele), 
anencephaly, and encephalocele.
Nuchal translucency (NT) − sonographic appearance of the collection of fluid under the 
skin at the back of the fetal neck. NT is a marker for chromosomal and other anomalies and 
can be measured in the first trimester of pregnancy.
Pre-eclampsia − a condition that occurs in some women during the second half of 
pregnancy, commonly associated with a rise in blood pressure and proteinuria.
Pregnancy-associated plasma protein A (PAPP-A) − a protein originating from the 
placenta used as a biochemical marker in first trimester combined screening for Down 
syndrome and other conditions.
Risk calculation algorithm − an explicit protocol (in this case computer based) that 
combines a number of factors in determining overall risk of a particular outcome or 
condition.
Screening − a way of identifying a group of people who are more likely than others to have 
a particular condition. The screening process involves testing people for the presence 
of the condition, and predicting the likelihood that they have the condition. Antenatal 
screening for Down syndrome and other conditions predicts the likelihood of the 
conditions being present in the fetus.
Sensitivity −the ability of screening to identify individuals with the condition screened 
for. A test with high sensitivity will have few false negative results.
Specificity − the ability of screening to identify individuals who do not have the condition 
screened for. A test with high specificity will have few false positive results.
Triploidy − an extremely rare chromosomal disorder in which a baby has three of every 
chromosome making a total of sixty-nine rather than the normal forty-six chromosomes.
Trisomy − a group of chromosomal disorders in which there are three copies, instead of 
the normal two, of a particular chromosome present in the cell nuclei. The most common 
trisomies in newborns are trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) 
and trisomy 13 (Patau syndrome).
Unconjugated oestriol (uE ) −a hormone produced by the placenta and used as a 
3
biochemical marker in second trimester maternal serum screening for Down syndrome 
and other conditions.
Further terms can be found at www.nsu.govt.nz
Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners 57

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Document Outline

• Antenatal Screening for Down Syndrome and Other Conditions Guidelines for health practitioners
• Antenatal and newborn screening
  • Acknowledgements
  • Contents
• Key Messages
• 1. Introduction
• 2. Background
  • 2.1 Overview of antenatal screening for Down syndrome and other conditions
  • 2.2 The screening options
  • 2.3 Screening performance
  • 2.4 Potential benefits and harms of antenatal screening for Down syndrome and other conditions
• 3. General Requirements
  • 3.1 Code of Health and Disability Services Consumers’ Rights
  • 3.2 Health Information Privacy Code
  • 3.3 Ensuring services meet the needs of women
• 4. The Screening Pathway
• 5. Documentation
• 6. Informed Choice – Consent or Decline
  • 6.1 Initial discussion
• 7. The Screening Tests
  • 7.1 Timing of first trimester combined OR second trimester maternal screening tests
  • 7.2 Ordering tests
  • 7.3 Completing the screening request form
• 8. Receiving and Communicating Results
• 9. Diagnostic Testing
• 10. Genetic Services and Other Referrals
• 11. Nuchal Translucency (NT) Scan
• 12. Screening Laboratory Processes
• 13. Data, Information and Monitoring
  • 13.1 Data and information collection
  • 13.2 Uses of data and information
  • 13.3 Monitoring
• Appendix 1: Resources and Contacts
• Appendix 2: Screened Conditions
• Appendix 3: Robinson Equation
• Glossary of Terms

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