Screening tests for Down syndrome are available during the first and second trimesters of pregnancy. These tests will only tell if your baby is at risk of Down syndrome. Further testing can then be done to provide a diagnosis.
Down syndrome is a genetic disorder that occurs at conception, that is when the egg is fertilized by a sperm. While most people have 23 pairs of chromosomes, people with Down syndrome have an extra copy of chromosome 21.
There are 3 types of screening tests that are available that tell you if your baby might be at risk of having Down syndrome. Further diagnostic tests can then be done to confirm the results.
Each test has advantages, disadvantages and limitations. The decision to have testing during pregnancy to determine the risk of Down syndrome is a personal one and it is best made when you have all the available information. You don't have to have prenatal testing if you don't wish to.
For detailed information about prenatal testing for Down syndrome, the Centre for Genetics Education has a comprehensive booklet.
Combined first trimester screening
This involves a blood test and an ultrasound scan.
Women may be offered 2 ultrasounds at the beginning of their pregnancy:
- a dating scan between weeks 6 and 14 of pregnancy
- if you choose to be screened for Down syndrome, a nuchal translucency scan between 11 weeks and 13 weeks and 6 days of pregnancy, combined with a blood test (called combined first trimester screening or CFTS).
At the nuchal translucency scan, the sonographer measures the thickness of the nuchal translucency (a pocket of fluid) at the back of your baby's neck.
You have the blood test between 9 and 14 weeks. The blood test measures the levels of two different hormones that occur naturally in your blood during pregnancy. When there's a genetic condition the levels of these hormones are usually abnormal.
The information from the blood test is combined with your age and the nuchal translucency measurement and used to work out your individual chance of having a baby with Down syndrome.
If it has not been possible for you to have the combined screening test in early pregnancy, you may be offered a different blood test between 14 and 20 weeks.
This test is called 2nd trimester maternal serum screening (2TMSS) test Non-invasive prenatal testing (NIPT).
A new blood test has become available that screens for Down Syndrome and two other related genetic disorders. It tests foetus DNA in the mother's blood, and while very accurate is still a screening test, so if it comes back as being abnormal (positive), then a diagnostic test will still be required (see below).
Tests are are currently around $400-500. It can be done from around 10 weeks, and while it may replace CFTS, it shouldn't replace the 12-week ultrasound as this also screens for structural problems such as spina bifida.
Second trimester screening
If it has not been possible for you to have the combined screening test or the NIPT in early pregnancy, you may be offered a different blood test between 14 and 20 weeks.
This test is called 2nd trimester maternal serum screening (2TMSS) test) and measures proteins associated with pregnancy. This information is combined with your age and used to work out your individual chance of having a baby with Down syndrome.
If the screening tests come back indicating that there is a risk that your baby may have Down syndrome, your midwife or doctor will explain the results to you and help you to decide whether you want to have further testing. One of your options will be to have a further diagnostic test which provides a definite answer.
The diagnostic test will either be by chorionic villus sampling (CVS) or amniocentesis. Your midwife or doctor will explain the result to you and help you to decide whether you want to have further testing.
Dealing with the results
It's always difficult when you're told that something is wrong with your baby, especially if you're faced with a painful decision about the future of your pregnancy.
Your midwife or doctor will make sure you see the appropriate health professionals to help you get all the information and support you need so you can make the right choices for you and your family.
Read more about caring for a child with Down syndrome.
Down Syndrome Association has information and services available to parents, including being able to speak to a parent of a child with Down syndrome.
You can also call Pregnancy, Birth and Baby on 1800 882 436 if you have any questions or would like to speak with a counsellor.
Last reviewed: December 2017