Frequently asked questions

These questions and answers should be read in conjunction with the Antenatal Screening for Down Syndrome and Other Conditions: Guidelines for health practitioners, published February 2013. Please note, these guidelines are currently being reviewed and an updated version will be available online in 2023.

1. What screening options are available?

2. Does the woman pay for this screening?

3. For first trimester combined screening should woman have their bloods or NT done first?

4. What drove the development of the quality improvements implemented from February 2010?

5. What are the aims of the quality improvements?

6. Who has the NSU worked with in the development of the quality improvements?

7. Who does the risk calculation?

8. What is the expected turnaround time from the laboratory for the results?

9. Why was this model of service provision chosen?

10. How should the new laboratory form be completed?

11. How do ultrasound providers use the forms for Section 88 claiming and audit purposes?

12.What should the NT report include/exclude for first trimester combined screening?

13. How does this affect Fetal Medicine Foundation (FMF) audit and accreditation requirements for ultrasound providers?

14. How do I generate an NT report for the first trimester using FMF software, without the risk assessment included?

15. How do these changes affect the accreditation requirements of ultrasound providers under the Maternity Services Notice?

16. What should the sonographer/radiologist discuss with the woman in relation to the NT scan for first trimester combined screening?

17. What happens if the NT scan indicates that there may be a fetal anomaly or pregnancy complication?

18, How can an ultrasound provider get the blood test results urgently if required?

19. What happens if women do not have their blood tests or insist that they only want an NT scan?

20. What happens if the laboratory has only received one component (blood or NT scan) for first trimester combined screening?

21. What happens if the first trimester bloods are grossly abnormal but the laboratory has not yet received the scan results?

22. Why is the gestational age reported in the screening results sometimes different from the gestational age calculated from the last menstrual period (LMP) by the referrer and does this mean the referrer needs to change the estimated date of delivery (EDD)?

23. Why does the laboratory sometimes tell me that the gestational age by scan was more than 13 weeks and 6 days so that second trimester bloods were done, when the scan report states that the gestational age is 13 weeks and 5 days and I have ordered first trimester combined screening?

24. Why can’t I order second trimester maternal serum screening to screen for neural tube defects (NTDs) when the woman has had first trimester combined screening, as this does not give an estimation of risk for NTDs?

25. What are the detection rates and false positive rates for the new screening options?

1. What screening options are available?

There are two screening options for antenatal screening for Down syndrome and other conditions in New Zealand, one in the first trimester or one in the second trimester.  This is a universal offer for women of all ages.

Option 1: First trimester combined screening

First trimester combined screening should be offered to all women 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 10 and 12 weeks). The two analytes measured in the screening test are pregnancy-associated plasma protein A (PAPP-A) and beta-human chorionic gonadtrophin (βhCG). This test is fully funded by the Ministry of Health
• a Nuchal Translucency (NT) scan. This is an ultrasound scan which can be carried out between 11 weeks and 13 weeks and 6 days of pregnancy. NT scans are funded under Section 88 however there may be a surcharge applied by private providers. The combined risk result is calculated by the laboratory and reported to the referring provider. The risk is calculated from the NT scan result, the maternal serum screening test result, and other factors including maternal age and weight, gestation and family history. Women 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 risk 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 women who present after 14 weeks and before 20 weeks of pregnancy, or who have not completed first trimester combined screening.

Second trimester maternal serum screening replaces the existing MSS2 triple test and now includes four analytes, beta-human chorionic gonadtrophin [βhCG], alpha-fetoprotein [AFP], unconjugated oestriol [µE3], and inhibin A. The risk result will be calculated by the laboratory and reported to the referring practitioner. This test is fully funded by the Ministry of Health.

In line with the changes being implemented, the combination of second trimester MSS2 and NT is no longer a recommended primary screening option.

2. Does the woman pay for this screening?

Both first and second trimester maternal serum screening blood tests are free to women (publicly funded). The existing part-charges for the Nuchal Translucency (NT) scan will still be charged by ultrasound providers.

3. For first trimester combined screening should woman have their bloods or NT done first?

For first trimester combined screening it is recommended that women have their bloods taken first and their NT done second. This is consistent with the optimal timing for each screening test.

4. What drove the development of the quality improvements implemented from February 2010?

In 2005 the NSU 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 now being implemented.

5. What are the aims of the quality improvements?

The aims of the quality improvements are to bring New Zealand into line with international best practice for antenatal screening for Down syndrome and other conditions by:

• improving the quality and safety of screening
• improving the consistency of support and information given to women
• reducing the number of women being offered invasive diagnostic tests based on NT or age-based screening.

6. Who has the NSU worked with in the development of the quality improvements?

The NSU has worked with representatives from:

• Royal Australian and New Zealand College of Radiologists (RANZCR)
• Genetic Services
• Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG)
• New Zealand College of Midwives (NZCOM)
• Royal Australian College of General Practitioners (RANZCGP)
• Maternity Services Consumer Council
• NZ Down Syndrome Association
• Laboratory Services
• Office of Disability Issues.

7. Who does the risk calculation?

All risk calculations are carried out by the laboratory using Lifecycle, an internationally recognised PerkinElmer platform.

First trimester combined screening

After completing the scan, ultrasound providers fax a copy of the NT scan request form and scan report to the laboratory. The NT scan results will be combined with the maternal serum screening results, and other factors such as maternal age and weight, gestation and family history, to provide one combined risk result.

Second trimester maternal serum screening

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

8. What is the expected turnaround time from the laboratory for the results?

Blood sample transit times to the laboratories may vary. The laboratory will report all first trimester combined screening tests within three business days of receiving the blood sample and scan information. All increased risk results will be phoned to the referrer within 24 hours of the result being available.

9. Why was this model of service provision chosen?

The decision to have the risk 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. This allows details about the woman and pregnancy, biochemistry results and NT information to be kept in one place, which facilitates quality monitoring and national consistency. The approach also fits with the Lead Maternity Carer (LMC) model of care. The LMC is the professional the woman has established a relationship with, and is the person who has the full clinical picture to inform discussions with the woman. The LMC is responsible for explaining the screening pathway, gaining informed consent, ordering the tests, explaining results to women, discussing options and making any referrals.

10. How should the new laboratory form be completed?

The combined/maternal serum screening lab form consists of two pages – the Lab Request on the top layer, and the NT scan request underneath. The form has a carbon backing so the information completed on the top layer will copy through to the NT request underneath. The only additional field that needs to be completed on the NT scan request form is the tick box on the right hand side ‘NT scan for first trimester combined screening’.

If the ultrasound provider is given both copies, please return the lab request to the woman.

For second trimester maternal serum screening, only the top layer is needed, as there is no radiology component. The second layer can be discarded.

11. How do ultrasound providers use the forms for Section 88 claiming and audit purposes?

After faxing the NT scan request form and scan results to the laboratory, the ultrasound provider should retain the NT scan request form for Section 88 claiming and audit purposes.

12. What should the NT report include/exclude for first trimester combined screening?

Please see Example Report 1 and Example Report 2. All reports must exclude a risk assessment for Down syndrome and other conditions. However reports should continue to include everything else they currently do.

Ultrasound providers may like to consider including the statement ‘In line with the requirements of the Ministry of Health, we no longer include a risk assessment for Down syndrome in this report’.

13. How does this affect Fetal Medicine Foundation (FMF) audit and accreditation requirements for ultrasound providers?

Current FMF requirements are not affected.

14. How do I generate an NT report for the first trimester using FMF software, without the risk assessment included?

As the NT scan is undertaken, the ultrasound report can be printed prior to pressing the ‘calculate risk’ button. The report will then exclude the numbers in the section headed ‘Estimated risk for Trisomy 21 (Down syndrome) 18 (Edwards syndrome) + 13 (Patau syndrome)’.  The three graphs will still appear, just without the arrows on the third graph. Once the report has been printed, press the ‘calculate risk’ button and the data will be recorded in the FMF database in line with audit/accreditation requirements.

15. How do these changes affect the accreditation requirements of ultrasound providers under the Maternity Services Notice?

Accreditation requirements as described under DC5 of the Notice remain unchanged.

16. What should the sonographer/radiologist discuss with the woman in relation to the NT scan for first trimester combined screening?

Ultrasound providers should continue to discuss the scan with the woman. However ultrasound providers must no longer discuss the risk assessment for Down syndrome and other conditions with the woman (eg, 1:300 risk). The Ministry of Health no longer recommends having a nuchal translucency scan without a blood test in the first trimester to screen for Down syndrome and other conditions. Having a nuchal translucency scan in isolation is no longer considered an optimal screening test. First trimester combined screening (blood and nuchal translucency) is in line with international best practice for risk assessment in pregnancy.

17. What happens if the NT scan indicates that there may be a fetal anomaly or pregnancy complication?

The ultrasound provider will contact the referrer to discuss the situation and further referrals, as is current practice. The agreement of the woman to participate in screening does not change the pathway for specialist referral. However:

• the woman still needs to have her first trimester bloods taken
• a copy of the NT report still needs to be sent to the laboratory
• a written report still needs to be sent to the referrer.

If there is a high NT, but the laboratory calculates a low risk of Down syndrome or other condition in the first trimester, the laboratory report will highlight the NT result and include the comment: "Specialist consultation is indicated if this has not already occurred."

If the NT is high, it is suggested ultrasound providers consider including a recommendation for a fetal anatomy scan in the second trimester in their report to the referrer.

18. How can an ultrasound provider get the blood test results urgently if required?

In circumstances where the ultrasound provider is concerned (eg, if there is a frank fetal anomaly or the NT is above the 95th centile) and the woman has already had her blood test, the ultrasound provider can ring the laboratory for an urgent result. This step will ensure all results (blood and NT) are taken into account before any advice is given to the woman and her maternity provider.

Ultrasound providers in the district health board (DHB) catchment areas of Northland, Waitemata, Counties Manukau, Auckland, Waikato, Lakes and Bay of Plenty can ring LabPLUS on 0800 522 7587. Ultrasound providers in all other DHB catchment areas can ring Canterbury Health Laboratories on 0800 843 522.

19. What happens if women do not have their blood tests or insist that they only want an NT scan?

The responsibility for explaining this screening and the reasons for the change lies with the referrer, not the ultrasound provider. If a woman presents with the new combined/maternal serum screening lab form, she will have completed an informed consent process and is expecting to receive a single first trimester combined risk result from her maternity provider.

However:

• if a woman presents at the ultrasound provider with a standard radiology request form requesting NT scanning rather than the first trimester combined screening form, then the ultrasound provider should have a discussion with the woman about the change in practice, and explain that an NT scan by itself is no longer recommended by the Ministry of Health. This is because the combination of blood test results and the NT scan gives an optimal risk assessment for the pregnancy
• if the woman agrees to combined first trimester screening the ultrasound provider would then complete the NT scan and fax the results to the laboratory and give the woman* and referrer the results (ie, measurements only— refer to sample report form). If possible, identify on the faxed referral form that the woman is going to ask for a referral for bloods. Alternatively, in consultation with the original referrer, the radiologist can write the blood request form.

(*if an ultrasound provider has not historically provided copies of scan reports to women, they are not required to do so now)

• in the event that the woman states to the ultrasound provider that it is her choice to have NT alone and she chooses not to have first trimester combined screening (in the full knowledge that this is no longer recommended by the Ministry of Health), she has declined participation in first trimester combined screening and the NT scan is completed outside of the quality improvement initiatives. In this case the ultrasound provider should complete the NT scan along with interpretation of results and send the results to the referrer, noting the woman has declined first trimester combined screening so an NT risk assessment has been completed.

20. What happens if the laboratory has only received one component (blood or NT scan) for first trimester combined screening?

The laboratory will contact the referrer in the 12th week to check if the woman is still intending to complete first trimester combined screening. The referrer will then follow up as necessary. If a woman does not complete first trimester screening, second trimester maternal serum screening remains an option for her.

21. What happens if the first trimester bloods are grossly abnormal but the laboratory has not yet received the scan results?

In these circumstances, the laboratory will discuss the results with the referrer immediately.

22. Why is the gestational age reported in the screening results sometimes different from the gestational age calculated from the last menstrual period (LMP) by the referrer and does this mean the referrer needs to change the estimated date of delivery (EDD)?

The software used by the laboratory to calculate the combined risk result in first trimester combined screening is designed to work using the gestational age calculated by scan measurements. There should be no change to your usual clinical practice regarding changing the EDD because of a difference between the scan EDD and EDD as estimated by sure LMP.

If the EDD calculated by ultrasound measurements gives a gestational age of more than 13 weeks and 6 days when either bloods or scan are completed, a combined risk calculation is not possible and the woman will be offered the opportunity to have second trimester maternal serum screening.

When ultrasound estimation of gestational age is available it is also used in the calculation of second trimester maternal serum screening results rather than the gestational age as estimated by LMP. Again this is because the software used is calibrated to provide the best estimation of risk using ultrasound estimation of gestational age. Where ultrasound EDD is not available the EDD from known LMP is used.

23. Why does the laboratory sometimes tell me that the gestational age by scan was more than 13 weeks and 6 days so that second trimester bloods were done, when the scan report states that the gestational age is 13 weeks and 5 days and I have ordered first trimester combined screening?

Some ultrasound providers report the gestational age from scan as being the same as the gestational age by LMP if the difference between the two is insufficient to qualify for a change in dates by ultrasound measurement. The ultrasound measurement CRL is used in the calculation for combined first trimester screening, rather than the gestational age. If the CRL is greater than that expected at 13 weeks and 6 days the first trimester combined screening calculation cannot be made.

24. Why can’t I order second trimester maternal serum screening to screen for neural tube defects (NTDs) when the woman has had first trimester combined screening, as this does not give an estimation of risk for NTDs?

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 risk of trisomies. Elevated levels of AFP can indicate the presence of NTDs. The use of AFP as a screening tool for NTDs is however neither very sensitive nor specific so is not considered best practice internationally.

Neural tube defects are most effectively identified during the ultrasound anomaly examination, usually performed at 18 to 20 weeks gestation, 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 18 to 20 week anomaly scan. If second trimester serum screening identifies an increased risk of NTD because of elevated AFP levels, this will be reported as are other incidental findings from screening. However, second trimester maternal serum screening should not be ordered with the intention of screening for NTD. The 18-week anomaly scan is the best available screening tool in this instance.

Women may have either first trimester combined or second trimester maternal serum screening. Funding is not available for both options unless, for some reason, first trimester combined screening was not completed.

Please note: From 1 March 2023, chance of NTD is no longer being reported.

25. What are the detection rates and false positive rates for the new screening options?

Discussions about the sensitivity (detection rate) and specificity (false positive rate) of screening options for antenatal screening for Down syndrome and other conditions tend to quote Serum, Urine and Ultrasound Screening Study (SURUSS) data. This is because the SURUSS study was, and still is, the largest and most comprehensive population-based report on this topic (Wald NJ, Rodeck C, Hackshaw AK et al. First and second trimester antenatal screening for Down syndrome: the results of the SURUSS. Health Technology Assessment 2003;7(11). It is important to note that the reported sensitivity and specificity are only relevant to the detection of Down syndrome, not any of the other conditions that may be indicated by screening.

The NSU has developed online learning resources about screening, and the screening initiatives it manages. Unit. Section 4 of the Quality Improvements in Antenatal Screening for Down Syndrome and Other Conditions Module provides detailed information about the screening options.

In the future, it will be possible to report on our own New Zealand data, but as the screening options are new, we are not able to do this now. The table below provides information about the sensitivity and specificity of the current screening options, from the SURUSS study.