Down syndrome is a genetic disorder that causes learning disabilities as well as some physical characteristics. Most babies with Down syndrome are identified during pregnancy. How can we tell which babies are affected?
Screening Tests and Diagnostic Tests
It is important to be aware of the difference between screening and diagnostic tests for Down syndrome. Screening tests can only tell you if your baby is at higher or lower risk of being affected. Most higher risk babies will have Down syndrome, but some will not. Most lower risk babies will not have Down syndrome, but a small number will still be affected. Only a diagnostic test can confirm if your baby is affected.
How We Screen for Down Syndrome in Pregnancy
All pregnant women in the UK will be offered a Nuchal Translucency scan
at around 12 weeks. The ultrasound must be performed between 11 weeks 5 days and 13 weeks 5 days in order for the Nuchal Translucency test to be possible. The test involves measuring the nuchal fold at the back of the baby’s neck and the Nasal bone. The measurement will be combined with other information, such as your age, in order to assess the chances that your baby has Down syndrome.
Another form of screening for Down syndrome has also become available in the UK recently. Non-invasive Prenatal Testing or NIPT is a blood test that can detect babies at risk of Down syndrome
. NIPT can be performed at any time after 10 weeks and it is more than 99% effective at detecting Down syndrome. This means that 99 out of 100 babies with Down syndrome would be given a high risk NIPT result.
What Happens Next?
If the screening tests suggest that your baby is at higher risk of Down syndrome, you will be able to discuss the results with our Advanced Sonographer or Consultants . You can also talk to your Midwife or Obstetrician . We’ll provide a full report on your ultrasound or NIPT results so that they have all of the relevant information.
You will get all the support you need to decide on your next steps, which might include arranging a diagnostic test. Diagnostic tests are only recommended if you get a higher risk result from your screening tests. Depending on the length of your pregnancy, you might be able to have amniocentesis or Chorionic Villus Sampling (CVS). Both involve taking a sample from inside your womb using a fine needle. Since these are both invasive tests, there is a small risk of complications including miscarriage. However, these are the only tests that can confirm the diagnosis for sure. We’ll help you to understand your screening test results and to decide if you want to go on to have a diagnostic test.