What happens with Down's syndrome testing? We break it down so you know what’s what.
Down's syndrome screening tests – the combined test
All pregnant women in England are offered a screening test called the combined test between 10 and 14 weeks of pregnancy (NHS Choices, 2018a). This test combines an ultrasound scan with a blood test for Down's syndrome, Edwards' syndrome and Patau's syndrome. It’ll tell you how high your chances are of having a baby with one of those conditions (NHS Choices, 2018a).
At the test, the fluid at the back of the baby's neck will be measured to determine the ‘nuchal translucency’. Nuchal translucency is the name for the fluid under the skin at the back of the baby’s neck. As the NT increases, the chance of Down’s Syndrome increases (NHS Choices, 2018a).
You will also have blood taken to check the levels of two pregnancy hormones. These two tests will then be put together with your age to work out the chance of your baby having Down's syndrome, Edwards' or Patau's syndromes (Basingstoke and North Hampshire NHS Trust, 2010; Shiefa et al, 2013; Basingstoke and North Hampshire NHS Foundation Trust, 2016; Insider Radiology, 2017).
Down's syndrome screening tests – the quadruple test
Getting a nuchal translucency measurement depends on the position of the baby so it’s not always possible to do it. If it’s tricky in your case, you’ll be offered a different blood screening test, called the quadruple test, which isn’t as accurate as the combined test (NHS Choices, 2018a).
Down's syndrome screening tests – results
If your screening test returns a lower-chance result, the chances of your baby having Down's syndrome are less than one in 150 (NHS Choices, 2018a).
If you have a higher-chance result, you will be offered a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS). This will tell you for certain whether or not the baby has Down's syndrome, Edwards' or Patau's syndrome (Health Knowledge, 2017; NHS Choices, 2018a).
Down's syndrome tests – non-invasive pre-natal testing (NIPT) or cell free DNA test (cfDNA)
If your screening test shows a higher chance, you can also take a more accurate screening test, such as NIPT for Down's syndrome test. It's also called the cell free DNA test (cfDNA). Currently, NIPT is being rolled out on the NHS but private health care providers can also do it for you (ARC, 2018; Gov.UK, 2019).
As the NIPT is a blood test, it does not carry a risk of miscarriage. The estimated number of miscarriages in the UK due to invasive testing could fall from 46 to three per year as a result of using the NIPT instead (Payne, 2016; Department of Health and Social Care, 2016).
If NIPT returns a high chance result for Down's syndrome, and you wish to know for certain, you can choose to have an invasive test. NIPT detects 98% of babies with Down's syndrome. The likelihood that your high chance result is correct can be as low as 46% if you are in your 20s, and have had no other screening. Your genetic counsellor or midwife will be able to advise you about this. There is also a calculator but it should always be used in discussion with your health professional (Positive about Downs, 2019).
Down's syndrome tests – the diagnostic test (amniocentesis or chorionic villus)
A diagnostic test like amniocentesis or chorionic villus sampling (CVS) will tell you for certain whether your baby has Down's, Edward’s or Patau's syndrome.
Amniocentesis involves removing and testing cells from the fluid that surrounds your unborn baby in the womb with a long, thin needle. Women usually have an amniocentesis between weeks 15 and 20 weeks of pregnancy but possibly later if necessary (NHS Choices, 2016).
With chorionic villus sampling, a small sample of cells is removed from the placenta. This is either by a needle inserted through your tummy or a tube or small forceps that go through the cervix. Women usually have a chorionic villus sampling test between weeks 11 and 14 weeks of pregnancy, or later if necessary (NHS Choices, 2018b).
About 0.5 to 1 in 100 amniocentesis or chorionic villus sampling tests result in a miscarriage so it’s a big decision whether to have them (NHS Choices, 2018b). The screening midwife at your maternity unit will discuss the further tests that are available with you.
Down's syndrome - specialist support available
If you have received a diagnosis for Down's syndrome based on one of the diagnostic tests, it is important to try to get as much information as possible. You could take a look at the following:
- Down’s Syndrome Association is a charity that provides information, support and advice to people with Down’s syndrome and their families. They also have information on affiliated local support groups.
- Mencap is a charity supporting people with learning disabilities.
- Positive About Down Syndrome shares real-life stories of other parents and what having a child with Down's syndrome means to them as a family. They can put you in touch with local support groups and families with a child or young person with Down's syndrome.
- There are many online support groups that can also offer support. If you are pregnant and had a high chance/positive result there is a closed Facebook page exclusively for those in your situation.
- If you have recently had a baby with Down syndrome a warm welcome awaits you on Positive about Down syndrome's page.
This page was last reviewed in May 2018.
Our support line offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0300 330 0700.
We also offer antenatal courses which are a great way to find out more about birth, labour and life with a new baby.
Make friends with other parents-to-be and new parents in your local area for support and friendship by seeing what NCT activities are happening nearby.
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