Down's syndrome testing in pregnancy

What happens with Down's syndrome, Edwards' syndrome and Patau's syndrome testing? We break it down so you know what’s what.

Antenatal screening is optional and should be carefully considered together with your partner. You might want to find out about different conditions, such as Down syndrome, before screening so that you understand what it is and what living with the condition means. This can help you understand what you're screening for in order to make an informed decision about whether to screen or not, and be prepared for your scan.

It's worth considering whether you would act on any results or not, as this may influence whether you go ahead with screening or not. If you choose not to screen for genetic conditions you can still have other scans and get your photos.

You can find lots of information and support from The Down's Syndrome Association (DSA) and Positive about Downs with features and stories written by parents and young people with Down syndrome. Visit SOFT (Support for Trisomy 13/18) for information about Edward’s or Patau's syndrome.

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 your baby having a genetic condition 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).  

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).

Screening test results

If your screening test returns a lower-chance result, the chances of your baby having the condition 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).

Non-invasive pre-natal testing (NIPT) or cell free DNA test (cfDNA)

If your screening test shows a higher chance, you can can consider taking NIPT. It's also called the cell free DNA test (cfDNA). NIPT has not been rolled out fully by the NHS  but private health care providers often offer this.

NIPT is a blood test taken from mum, as such it does not carry a risk of miscarriage. However, it is not diagnostic so if NIPT returns a high chance result, and you wish to know for certain, you would need to have an invasive test.

The accuracy of the high chance result being correct can be as low as 48% if you are in your 20's, 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).

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.

Specialist support available

If you have received a diagnosis or high chance result for any of conditions, it's 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.
  • If you've received a diagnosis/high chance for Edward’s or Patau's syndrome, visit SOFT (Support for Trisomy 13/18).

This page was last reviewed in May 2018.

Further information

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.

Antenatal Results and Choices (ARC) (2018) Screening for Down’s, Edwards and Patau’s Syndrome/Non-invasive Pre-natal Testing (NIPT). Available from: http://www.arc-uk.org/tests-explained/non-invasive-prenatal-testing-nipt [Accessed 3rd May 2018]

Basingstoke and North Hampshire NHS Foundation Trust. (2016)  Low PAPP-A Information for parents. Available from:  https://www.hampshirehospitals.nhs.uk/media/423511/low_papp-a.pdf [Accessed 3rd May 2018]

Department of Health and Social Care. (2016) Safer screening for women Available at: https://www.gov.uk/government/news/safer-screening-test-for-pregnant-wo… [Accessed 28th May 2019]

Fishler K, Koch R. (1991) Mental development in Down syndrome mosaicism. American Journal on Mental Retardation 96(3):345-351. Available from:  https://www.ncbi.nlm.nih.gov/pubmed/1836734 [Accessed 3rd May 2018]

Gov.UK. (2019) Update on NIPT implementation — microarray testing technology and twins. Available from:
https://phescreening.blog.gov.uk/2019/06/17/update-on-nipt-implementati…; [Accessed: 5th August 2019]

Health Knowledge (2017) Differences between screening and diagnostic tests and case finding. Available from: https://www.healthknowledge.org.uk/public-health-textbook/disease-causation-diagnostic/2c-diagnosis-screening/screening-diagnostic-case-finding [Accessed 3rd May 2018]

Inside Radiology. (2018) Nuclear translucency scan. Available from: https://www.insideradiology.com.au/nuchal-translucency-scan/ [Accessed 3rd May 2018]

Mégarbané A, Noguier F, Stora S, Manchon L, Mircher C, Bruno R, Ravel,A. (2013). The intellectual disability of trisomy 21: differences in gene expression in a case series of patients with lower and higher IQ. European Journal of Human Genetics 21(11):1253. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23422941 [Accessed 3rd May 2018]

NDSS (National Down Syndrome Society). (2018) Down syndrome. Available from:  https://www.ndss.org/about-down-syndrome/down-syndrome/ [Accessed 3rd May 2018]

NHS Choices. (2016) Amniocentesis. Available  from:  https://www.nhs.uk/conditions/amniocentesis/ [Accessed 3rd May 2018]

NHS Choices. (2017) Down’s syndrome. Available from: https://www.nhs.uk/conditions/downs-syndrome/ [Accessed 3rd May 2018]

NHS Choices. (2018a) Screening for Down’s, Edwards’ and Patau’s syndrome. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/screening-amniocentesis-downs-syndrome/ [Accessed 3rd May 2018]

NHS Choices. (2018b) Chorionic villus sampling. Available from:  https://www.nhs.uk/conditions/chorionic-villus-sampling-cvs/  [Accessed 3rd May 2018]

NIH National Human Genome Research Institute. (2016) Chromosome abnormalities. Available from: https://www.genome.gov/11508982/chromosome-abnormalities-fact-sheet/#al-5 [Accessed 3rd May 2018]

Payne J. (2016) Amniocentesis. Available at: https://patient.info/doctor/amniocentesis-pro [Accessed 26th May 2019]

Positive about Downs. (2019). Available from https://positiveaboutdownsyndrome.co.uk/

Shiefa S, Amargandhi M, Bhupendra J, Moulali S, Kristine T. (2013). First trimester maternal serum screening using biochemical markers PAPP-A and free β-hCG for down syndrome, patau syndrome and edward syndrome. Indian Journal of Clinical Biochemistry 28(1):3-12. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24381414 [Accessed 3rd May 2018]

 

Further reading

American Pregnancy Association (2016) Quad screen test. Available from:  http://americanpregnancy.org/prenatal-testing/quad-screen/ [Accessed 3rd May 2018]

Basingstoke and North Hampshire NHS Foundation Trust. (2016)  HCG information leaflet. Available from: http://www.hampshirehospitals.nhs.uk/uploaded_files/GP%20section/EPAU/hcg_info_leaflet_march2010.pdf [Accessed 3rd May 2018]

NHS Choices. (2016)  Mid-pregnancy anomaly scan. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/anomaly-scan-18-19-20-21-weeks-pregnant/ [Accessed 3rd May 2018]

NHS Choices. (2017) The pregnancy dating scan. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/dating-scan-ultrasound-10-11-12-13-weeks-pregnant/ [Accessed 3rd May 2018]

NHS Choices. (2018) Screening tests in pregnancy. Available from:  https://www.nhs.uk/conditions/pregnancy-and-baby/screening-tests-abnormality-pregnant/ [Accessed 3rd May 2018]

NIH U.S. National Library of Medicine. Health Conditions -Down syndrome https://ghr.nlm.nih.gov/condition/down-syndrome#inheritance [Accessed 3rd May 2018]

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