The world of screening and tests during pregnancy for conditions like Down’s syndrome can feel worrying and confusing. Here we break it down.
Why are antenatal screening tests offered?
When you’re pregnant, you’ll be offered a number of screening tests to try to find whether you or your baby have any health problems. You can have screening tests for things like infectious diseases, chromosomal differences like Down's syndrome and physical abnormalities (NHS Choices, 2018a).
A screening test estimates your chance of having a baby with a certain condition but cannot tell you for certain whether your baby has it.
"Screening tests are usually either scans or blood tests and won’t affect your baby or threaten their development in any way (they are non-invasive)."
A pregnancy scan or ultrasound scan uses high-frequency sound waves to create a moving image of your baby, their internal organs and your placenta. You will be able to see the image on a screen, and a picture is almost always available as a printout. A detailed anomaly scan is carried out at 18-21 weeks of pregnancy.
Pregnancy blood tests involve taking a sample of your blood and testing it for markers (such as hormone levels). This can tell you about the risks of certain conditions.
Find out more about pregnancy scans and screening in Antenatal screening in pregnancy.
This video shows when the best times for NHS antenatal and newborn screening tests are.
Are antenatal screening tests compulsory?
No, it’s completely up to you whether you have the tests or not (NHS Choices, 2018a). It's important to understand the purpose of all tests so you can make an informed decision about whether you want to have them (NHS Choices, 2018a). You can discuss this with your maternity team. It’s also possible to have screening for some conditions but not others.
What do antenatal screening tests involve?
Pregnant women are usually screened to check their health, and for conditions that might affect their baby's health during pregnancy. These tests may include blood tests and urine tests. Blood tests can show whether you have a higher chance of inherited disorders like sickle cell anaemia and thalassaemia. They can also show whether you have infections like HIV, hepatitis B or syphilis(NHS Choices, 2018a).
Screening tests for your baby involve ultrasound scans, blood tests or a combination. Ultrasound scans are used for detecting physical abnormalities like spina bifida, cleft lip or cardiac problems. Blood tests combined with scans can help find the chance of chromosomal differences, such as Down's syndrome, Edwards’ syndrome or Patau's syndrome (NHS Choices, 2018a).
Down's syndrome and other chromosomal condition tests: when are they done?
Ultrasound scans for Down's syndrome, Edwards’ syndrome and Patau’s syndrome can be done during the dating scan between 11 and 14 weeks of pregnancy (NHS Choices, 2018b). They are part of the ‘combined test’ along with a blood test. You can choose to have the dating scan without any testing.
At the scan, the fluid at the back of the baby's neck is measured. Your age and the information from these two tests are used to work out the chance of the baby having Down's syndrome, Edwards' syndrome or Patau's syndrome. You can choose to test for all three conditions, just Down's syndrome or just Edwards' syndrome and Patau's syndrome.
At 20 weeks, you’ll have an anomaly scan, which may detect conditions like spina bifida and cleft lip (NHS Choices, 2018c).
What's the difference between screening tests and diagnostic tests?
Screening tests usually identify the likelihood of baby having an infectious disease or a genetic condition. They are simple, cost-effective and non-invasive but they are not definite (Health Knowledge, 2017).
On the other hand, diagnostic tests can tell you whether your baby actually has a particular condition, such as Down's syndrome. But these tests are invasive and are potentially dangerous for the baby. They are only done if there is a strong chance and you feel you need to know whether your baby has a specific condition or not (Park et al, 2016; NHS Choices, 2018b).
What do diagnostic tests like chorionic villus sampling and amnicentisis involve?
Amniocentesis is a diagnostic test and involves removing and testing a small sample of cells from the amniotic fluid (the fluid that surrounds your unborn baby). Amniocentesis is usually done between weeks 15 and 20 of pregnancy but it may be later if necessary (NHS Choices, 2016).
Chorionic villus sampling (CVS) involves removing and testing a small sample of cells from the placenta and is usually carried out between weeks 11 and 14 of pregnancy, although it's performed later if needed too (NHS Choices, 2018d).
What are the risks associated with screening and diagnostic tests?
Screening tests don’t carry any risks to you or your baby but diagnostic tests are associated with a 0.5% to 1% chance of miscarriage (NHS Choices, 2016, 2018a, d).
This risk is higher if an amniocentesis is done before 15 weeks of pregnancy. Chorionic villus sampling carries a similar risk of miscarriage. In context though, compared with normal levels of miscarriage, the added risk is only 0.11% to 0.22% (Akolekar et al, 2015).
How do you decide whether to have Down's syndrome and other antenatal tests?
The NHS recommends some screening tests, like blood tests for infectious diseases, eye screening if you have diabetes and the newborn checks. This is because results from these tests can help make sure that you or your baby gets urgent treatment for serious problems (Public Health England and NHS, 2018). Beyond that though, the ball is usually in your court.
Before you decide whether to have each test, consider all of the information that’s available. But also bear in mind that screening tests can’t tell for certain whether your baby has a condition or not. Some tests might help you make informed decisions and prepare you though.
It might also help to think in advance how you would feel if your screening tests did indicate a potential problem. Think about how you’d feel if you were offered more tests or if you knew for certain that your baby has a health condition. Having a further test or termination will always be your decision and health professionals will support you, whatever you decide.
This page was last reviewed in March 2018
Our support line offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0300 330 0700.
To prepare yourself more for what happens during and after labour, we offer antenatal courses which are a great way to find out more about birth, labour and life with a new baby.
You might find attending one of our NCT New Baby groups helpful as they give you the opportunity to explore different approaches to important parenting issues with a qualified group leader and other new parents in your area.
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.
The NHS gives full information on the checks and tests offered in pregnancy.
Healthtalkonline offers shared experiences, videos and stories from 37 women and 8 couples from the UK. Topics include making decisions about screening, including those that have and have not ended the pregnancy.
Antenatal Results and Choices is a national charity that provides information to expectant and bereaved parents throughout and after the antenatal screening and testing process. Telephone helpline: 0845 077 2290.
RAPID (Reliable Accurate Prenatal non-Invasive Diagnosis) is a five-year UK national programme funded by the National Institute for Health Research to evaluate early non-invasive prenatal diagnosis (NIPD).
RCOG (Royal College of Obstetricians and Gynaecologists) offers a guidance sheet about amniocentesis and chorionic villus sampling.
Akolekar R, Beta J, Picciarelli G, Ogilvie C, D'antonio F. (2015) Procedure‐related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta‐analysis. Ultrasound in Obstetrics & Gynecology. 45(1):16-26. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25042845 [Accessed 27th March 2018]
Health Knowledge. (2017) Diagnosis and screening/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 27th March 2018]
NHS Choices. (2016) Amniocentesis. Available from: https://www.nhs.uk/conditions/amniocentesis/ [Accessed 27th March 2018]
NHS Choices. (2018a) Screening tests in pregnancy. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/screening-tests-abnormality-pregnant/ [Accessed 27th March 2018]
NHS Choices. (2018b) Screening for Down’s, Edwards’ and Patau’s syndrome. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/screening-amniocentesis-downs-syndrome/ [Accessed 27th March 2018]
NHS Choices. (2018c) Mid-pregnancy anomaly scan. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/anomaly-scan-18-19-20-21-weeks-pregnant/ [Accessed 27th March 2018]
NHS Choices. (2018d) Chorionic villus sampling. Available from: https://www.nhs.uk/conditions/chorionic-villus-sampling-cvs/ [Accessed 27th March 2018]
Park SY, Jang I, Lee MA, Kim YJ, Chun SH, Park MH. (2016) Screening for chromosomal abnormalities using combined test in the first trimester of pregnancy. Obstetrics & gynecology science. 59(5):357-366. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27668198 [Accessed: 27th March 2018]
Public Health England (2015) PHE screening. at https://phescreening.blog.gov.uk/2015/08/06/getting-animated-with-our-screening-timeline/ [Accessed: 27th March 2018]
Public Health England, NHS (2018) Screening tests for you and your baby. at https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/674470/Screening_tests_for_you_and_your_baby_booklet.pdf [Accessed: 27th March 2018]