Frequently asked questions

There are two screening options for antenatal screening for Down syndrome and other conditions in Aotearoa New Zealand, one in the first trimester or one in the second trimester. This is a universal offer for pregnant people of all ages. This screening is a way of assessing the chance of the baby having Down syndrome, Edwards syndrome, Patau syndrome and some other rare genetic disorders. Participation in this screening is entirely the pregnant person’s choice, and they also have the option to accept or decline further testing or referrals within the screening pathway.

Option 1: First trimester combined screening

First trimester combined screening should be offered to all people who present early in pregnancy. It includes both:

• a first trimester maternal serum screening test which can be taken between 9 weeks and 13 weeks and 6 days of pregnancy (ideally between 9 and 10 weeks). The two analytes measured in the screening test are pregnancy-associated plasma protein A (PAPP-A) and beta-human chorionic gonadotropin (βhCG). This test is fully funded by Health NZ | Te Whatu Ora.
• an ultrasound scan to measure nuchal translucency (NT) and crown-rump length (CRL), which is often referred to as the NT scan. The recommended timing for this scan is between 12 weeks and 13 weeks and 6 days of pregnancy. A surcharge may be applied by private providers for the NT scan.
• The combined screening result is calculated by the laboratory and reported to the referring health practitioner. The result is calculated from the NT scan information, the maternal serum screening test result, and other factors including gestation and maternal age and weight. People must be informed that they will receive one combined result, after they have had the blood test and scan. The incorporation of serum results in the screening calculation significantly increases the sensitivity and specificity of screening.

Option 2: Second trimester maternal serum screening

Second trimester maternal serum screening should be offered to all people who present after 14 weeks and before 20 weeks of pregnancy, or who have not completed first trimester combined screening. The optimal timing for the second trimester blood test is 14 to 18 weeks of pregnancy.

Second trimester maternal serum screening includes four analytes, beta-human chorionic gonadotropin [βhCG], alpha-fetoprotein [AFP], unconjugated oestriol [µE3], and inhibin A. The screening result is calculated by the laboratory and reported to the referring practitioner. This test is fully funded by Health NZ | Te Whatu Ora.

The screening result

Both first and second trimester screening will provide one of two results: either increased chance or low chance. The threshold for increased chance is 1:300.

Both first and second trimester maternal serum screening blood tests are free to pregnant people (publicly funded). A surcharge may be applied by ultrasound providers for the NT scan.

For first trimester combined screening it is recommended that pregnant people have their bloods taken first and their NT scan done second. This is consistent with the optimal timing for each component. However, it is also acceptable to do both blood test and scan at 12 weeks.

In 2005 the National Screening Unit commissioned Professor Peter Stone and Diana Austin to assess antenatal screening for Down syndrome in New Zealand. In their report they noted that, ‘the current screening process in New Zealand was identified as being a physical, emotional and social risk to families with the worst of all options being available and not in line with international research’ (Stone & Austin, 2006).

An advisory group was established in response to this work and developed the report Antenatal Down Syndrome Screening in New Zealand 2007. The report clearly identified that Nuchal Translucency (NT) alone was not an appropriate screening practice and the ‘worst of all options’ if NT was performed in isolation. Work then commenced on the development of the quality improvements which were introduced in 2010 and included incorporating maternal serum screening with ultrasound and providing practitioner guidelines and consumer resources.

Since 2010, further quality improvements to this screening have been considered and developed on an ongoing basis.

All screening calculations are carried out by the laboratories using a single database for probability calculation. This ensures consistent calculation of chance for all pregnant people in Aoteaora New Zealand. It also allows details about the person and pregnancy, biochemistry results and NT scan information to be kept securely in one place, which facilitates quality monitoring and national consistency.

First trimester combined screening

After completing the scan, ultrasound providers transmit a copy of the NT scan report to the screening laboratory. This is either LabPLUS for Taupō and everywhere north of Tāupo, or Canterbury Health Laboratories (CHL) for south of Taupō. The NT scan information is combined with the maternal serum screening results, and other factors such as gestation and maternal age and weight, to provide one combined screening result.

Second trimester maternal serum screening

The results of the four-analyte maternal serum screening test are combined with other factors such as gestation and maternal age and weight, to provide a screening result.

Laboratory advice

Health practitioners are welcome to contact the screening laboratory if they have any questions about the screening results.

LabPLUS        Phone: 0800 LABPLUS (0800 522 7587)

CHL               Phone: 0800 THE LAB (0800 843 522)

Blood sample transit times to the screening laboratories may vary but samples are generally received two to three days after collection. The laboratory will report all screening results within three business days of receiving all the information required to calculate the result. 

If the screening result is increased chance, the laboratory will contact the referring health practitioner within 24 hours of the result being available. The result will also be dispatched to the health practitioner by mail or electronically.

If the screening result is low chance, the laboratory will dispatch the result to the referring health practitioner by mail or electronically within 48 hours of the result being available.

The decision to have the screening calculation completed in the laboratory provides the broadest access, highest quality and most efficient and consistent service provision. The centralised model offers advantages for New Zealand, given factors such as minimum volumes, demand uncertainty and the shallow pool of expertise for interpreting the biochemical markers. Both first trimester combined and second trimester maternal serum screening are provided by the laboratory. The approach also fits with the Lead Maternity Carer (LMC) model of care. The LMC is the professional the pregnant person has established a relationship with, and is the person who has the full clinical picture to inform discussions with them and their whānau. The LMC is responsible for explaining the screening pathway, gaining informed consent, ordering the tests, explaining results, discussing options and making any referrals.

Screening request form

If the pregnant person accepts screening, the health practitioner (midwife or doctor) will complete the screening request form.

Download the Laboratory request form (PDF, 162KB)

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.

Crown-rump length (CRL) will be provided to the laboratory by the radiologist after nuchal scan completion, or referrers may provide a CRL measurement from an earlier dating scan if available.

Referral for nuchal translucency (NT) ultrasound scan

Specialist medical maternity services, including NT scans, may only be provided on referral from another practitioner (midwife or doctor).

This requires a written or electronic radiology referral. Referrals for the NT scan must be made in accordance with Section 94 of the Pae Ora (Healthy Futures) Act 2022.

For more information on maternity ultrasound scans see New Zealand Obstetric Ultrasound Guidelines.

Reporting templates for radiologists can be found within the New Zealand Obstetric Ultrasound Guidelines. 

The following information from the NT scan must be provided for this screening.

• NHI
• Demographic information (date of birth, name)
• Referrer’s name
• Date of NT scan
• NT and CRL measurements
• Multiple pregnancy (chorionicity and amnionicity)
• Other details that may inform the screening calculation
• Significant abnormalities which may change the management of the pregnancy
• Name of the practice, name of the radiologist, and the name and FMF number of the practitioner performing the scan.

All reports must exclude a risk assessment for Down syndrome and other conditions, as this is provided by the screening laboratories following completion of both the maternal blood test and the NT scan.

Health NZ | Te Whatu Ora recommends IANZ radiology accreditation for radiology providers, to provide assurance that the practice operates to established standards.

In New Zealand, the quality-of-service requirements relates to appropriate education and training for the measurement of NT. Appropriate certification is recognised through FMF London and the Australian Nuchal Translucency – Ultrasound, Education and Monitoring Program.

To support best practice, Health NZ | Te Whatu Ora provides information to radiology practices, radiologists, and NT practitioners on the quality of NT and CRL measurements.

More information

Working together on quality improvements for NT and CRL measurements

Ultrasound practitioners may discuss the findings of the NT scan with pregnant people but should not offer a calculation on the chance of Down syndrome and other conditions based on NT alone (e.g. 1:300 chance).

In all but exceptional circumstances, the screening result will be communicated to the pregnant person by the referring practitioner.

If the NT scan shows an obvious anomaly (eg, structural/anatomical anomaly), the radiologist should inform the referring health practitioner in a timely manner.

The referring health practitioner should discuss the results with the pregnant person and offer referral to a specialist obstetrician. Indications for referral to specialist obstetric services are outlined in the Guidelines for Consultation with Obstetric and Related Medical Services (Referral Guidelines).

Go to Guidelines for Consultation with Obstetric and Related Medical Services (Referral Guidelines)

If the NT scan shows a NT measurement ≥3.5mm, the ultrasound provider should discuss the scan results with the referring health practitioner.

The referring health practitioner should offer the pregnant person referral to a Fetal Medicine specialist (or local equivalent).

Completion of first trimester combined screening is still recommended. This will assist the specialist to develop a care pathway with a full clinical picture.

An early detailed fetal heart scan should be considered at 16 weeks gestation.

If both components have not been performed by 13 weeks 6 days, the screening laboratory will let the referring health practitioner know that first trimester combined screening cannot be completed and will recommend that second trimester maternal serum screening is offered. The health practitioner should let the pregnant person know that first trimester combined screening has not been completed and provide information about second trimester screening.

For first trimester combined screening, at the time the NT scan is performed the CRL must be between 45-84mm. If the CRL result is above 84mm, the screening laboratory will let the health practitioner know that first trimester combined screening cannot be completed because the person is in the second trimester. If the blood has also been taken in the second trimester, second trimester maternal serum screening can be performed, otherwise a new blood sample will be needed.

Screening accuracy is affected by correct estimation of gestational age. The most accurate screening result will be achieved when the best available dating method is used – in most cases this will be ultrasound assessment of CRL.

The order of precision for various methods of estimating gestational age is as follows.

• IVF
• Ultrasound assessment of CRL
• Last menstrual period (LMP)
• Clinical assessment

Neural tube defects are most effectively identified during the second trimester anatomy scan (19+ weeks), when the fetal head and spine can be visualised. Although they are sometimes identified during scanning at 12 weeks, up to 99 percent of babies with anencephaly and 90 percent of babies with spina bifida are identified at the second trimester anatomy scan.

Second trimester maternal serum screening is not considered the best option for screening for NTDs. Alpha fetoprotein (AFP) is included in second trimester maternal serum screening. It is one of four analytes which together give the chance of trisomies. Elevated levels of AFP can indicate the presence of NTDs. However, the use of AFP as a screening tool for NTDs is neither very sensitive nor specific so is not considered best practice internationally.

From 1 March 2023, chance of NTD is no longer included on the laboratory report provided to health practitioners.

Health NZ | Te Whatu Ora has national oversight of antenatal screening for Down syndrome and other conditions and produces annual monitoring reports. These reports provide New Zealand data on the detection rate and false positive rate of this screening. Other information provided in the annual reports includes screening completion rates, information about increased chance results, diagnostic testing volumes, and the positive predictive value of screening.

Published monitoring reports are available 

Go to Procedures, guidelines and reports page