Everything you need to know about screening for Down Syndrome.

Screening tests are available during pregnancy to assess the likelihood that your baby may have Down syndrome (Trisomy 21) and certain other chromosomal conditions. In New Zealand, these screening options include ultrasound assessment, blood tests, and non-invasive prenatal testing (NIPT).

At your booking appointment, we will discuss the screening options available to you and help you understand the benefits, limitations, and timing of each test so you can make an informed decision that feels right for you and your family. We do offer NIPT testing to be done at the time of your booking visit and results take 7-10 working days.

What is Down Syndrome?
Down syndrome, also known as Trisomy 21, occurs when a baby has an extra copy of chromosome 21. Chromosomes contain genetic information that influences growth and development.

Down syndrome occurs at conception and is not caused by anything parents did or did not do during pregnancy. The chance of having a baby with Down syndrome increases with maternal age, although it can occur in pregnancies at any age and in all ethnic groups.

Children with Down syndrome have varying degrees of intellectual disability and may have associated medical conditions, although many lead healthy, fulfilling lives with appropriate support and care.

For additional information and support resources, please refer to: NZ Down Syndrome Association

First Trimester Combined Screening
For women booking for antenatal care during the first trimester, the standard screening option in New Zealand is the first trimester combined screening test.

This involves:

A blood test performed between 9 and 14 weeks of pregnancy
A specialised ultrasound scan, called a nuchal translucency (NT) scan, performed between 11 and 14 weeks

The screening combines:

Maternal age-related risk
Levels of pregnancy hormones in the blood (PAPP-A and free beta-hCG)
Measurement of fluid at the back of the baby’s neck (nuchal translucency)
These factors are used to calculate an individualised estimate of the likelihood that your baby may have Down syndrome or certain other chromosomal conditions, including Trisomy 13 and Trisomy 18.

Results are provided as a probability, for example:

1 in 500
1 in 2,000
A lower number represents a higher chance, while a larger number represents a lower chance.

Combined screening is a screening test, not a diagnostic test. It cannot confirm whether or not a baby has Down syndrome, but it can provide a more accurate assessment of risk and help determine whether further testing should be considered.

The combined screening test detects approximately 80–85% of pregnancies affected by Down syndrome. It is important to understand that no screening test can detect all affected pregnancies.

The nuchal translucency ultrasound may also identify some early structural abnormalities, although many conditions cannot be detected at this stage of pregnancy.

Non-Invasive Prenatal Testing (NIPT)
Non-Invasive Prenatal Testing (NIPT) is a newer screening option available from 10 weeks of pregnancy onwards. This test analyses small amounts of your baby’s DNA circulating in your bloodstream to assess the likelihood of certain chromosomal conditions, including Down syndrome.

NIPT is more accurate than standard combined screening; however, it is still considered a screening test rather than a definitive diagnostic test.

At present, NIPT is generally not publicly funded in New Zealand and is usually arranged privately.

Diagnostic Testing
If screening results indicate an increased likelihood of a chromosomal condition, some women may choose to have diagnostic testing such as:

Chorionic Villus Sampling (CVS)
Amniocentesis
These tests can provide a definitive diagnosis but are invasive procedures and carry a small risk of miscarriage.

For many women, screening tests provide reassurance and may help avoid the need for invasive testing. If you receive a higher-risk result, we will discuss your options carefully and provide support and referral where appropriate.

Second trimester serum screening for Down Syndrome
Women booking for antenatal care after 14 weeks of pregnancy (too late for a nuchal translucency ultrasound scan) can still have a screening blood test. This is called second trimester serum screening. This can be done at up to 20 weeks of pregnancy (ideally between 14 and 18 weeks). This test also takes your chances based on your age alone and calculates a personal chance based on the levels of three different substances checked in your blood.

This later test is not quite as reliable as the combined first trimester test. There is no need to have this later test if you have already had the earlier combined test.

First and second trimester screening for placental cells in maternal blood
A newer screening test for Down Syndrome is also available privately (at a cost of about $600). This is a blood test that can be done after 10 weeks. The test measures the levels of baby’s placental DNA circulating in your blood. In all pregnancies very small amounts of “cell-free fetal DNA” can be detected in maternal blood. Higher levels of DNA related to chromosome 21 will be detected in your blood if your baby has Down Syndrome. This test is sometimes called “non-invasive pre-natal testing” or NIPT. NIPT will detect more than 99% of babies with Down Syndrome and is much less likely to give a non-reassuring “false-positive” result than the combined screening test. It can also detect high levels of DNA associated with trisomy 18 and 13.

You may also wish to do NIPT testing as an alternative to or in addition to the combined screening test. Some women have also had NIPT testing after a non-reassuring combined screening test result. NIPT testing may reassure them enough to not have an amniocentesis.

NIPT testing is not reliable enough to be considered a diagnostic test – not all women with a positive test will have a baby with Down Syndrome. However, a negative test reduces the chances that a woman is carrying a baby with Down Syndrome to well below 0.1 per cent. It is not currently part of the publicly funded national screening programme.

There are several different companies providing NIPT testing. AOC currently uses a test provided by the Victorian Clinical Genetic Services (VCGS) in Australia called PERCEPT. You can read more about the PERCEPT test by visiting the VCGS website or by downloading their patient information leaflet here.

Amniocentesis
This is a diagnostic test that will confirm if your baby does or does not have Down Syndrome. It is usually done at between 15 and 17 weeks of pregnancy. A needle is passed through your abdominal wall into the fluid around baby – an ultrasound scan is used to guide the needle and make it a safe procedure for baby. A small amount of fluid is drawn off. Within this fluid are some of baby’s skins cells that can be cultured in the laboratory to check baby’s chromosomes.

It can take 10 to 14 days to get a result from this test. A more rapid test (called FISH) is available that can check for Down Syndrome within 24 to 48 hours is also available but at an additional cost – the doctor performing your amniocentesis can discuss this option with you.

Amniocentesis is a quick procedure taking about 10 to 15 minutes to set up and only a few minutes to do. You are welcome to bring your partner or a support person along and should plan to have a quiet 48 hours after the test. It does have a small risk of miscarriage. For every 1,000 women having an amniocentesis one woman will miscarry as a result of the procedure.

Useful sources of information
For many couples, decision-making around Down Syndrome screening is straightforward and their test results are reassuring. All of us at AOC are aware that for some couples making these decisions is terribly difficult – we are very happy to talk to you by phone between appointments or arrange extra visits to clinic if you need more help in deciding what tests to have.

Down Syndrome screening is optional – you do not have to have any screening if that is your preference.

We can provide you with additional written information to help guide your decision-making. You can download our information leaflet on medical tests in pregnancy here. Useful websites are also listed on our Helpful Information page.