A consideration during your pregnancy is whether you would like to do testing for chromosomal conditions such as Down Syndrome. The information below will guide you as you consider testing.
When any test is done it is important to think through what you would do with the result. It is prudent to consider your next steps should the chromosomal test you choose come back with a high risk or positive test result. If you would act on that result, then it is appropriate for you to do the testing. However, should you not want to act on the result, and prefer not to have the anxiety of an inconclusive test during your pregnancy, then it is wise to consider whether you’d want screening at all. This is a very personal decision and one you should discuss with your partner so that you are able to truly “own” the decision you make.
Risk for chromosomal conditions such as Down Syndrome increases with age, for example when you are 25 years old your risk is about 1 in 800 of having a baby with Down Syndrome. That increases to about 1 in 250 when you are 35 years old.
There are two kinds of tests available when it comes to investigating this. Those that are screening tests and those that are diagnostic tests.
A screening test doesn’t give you a diagnosis. Instead, it calculates the chance of having a baby with a chromosomal condition. For example, if you are 25 year old your risk may change after a screening test from 1 in 800 to 1 in 5000 or 1 in 300 depending on the results. After the screening test you will then be classified as being at high risk (<1:300) intermediate risk (1:300 -1:1000) or low risk (>1:1000). You will have to decide what to do with this new risk calculation which includes whether you want to proceed with getting a diagnostic test.
Types of screening tests
There are a few different types of screening tests. You can also combine some of the tests. Like with most things, the more the tests costs the more accurate the information will be.
This is the most accurate screening test. It is also the most expensive screening test (R6500 – R8500). It is a blood test done after 10 weeks of pregnancy and is 99% accurate with a 1% false positive rate. The limitation is the cost, but if you are considered high risk (age over 40 or high risk after another test) then some medical aids will pay for this test.
- Other blood tests
Other basic blood tests can be done. There are two groups; one done between 8 and 14 weeks and another group done between 15 and 20 weeks of pregnancy. These tests have a 60% accuracy (meaning it will pick up 6 out of 10 babies with down syndrome) and a 5 % false positive rate (which means the test might falsely diagnose 5 in 100 pregnancies as having Down Syndrome, when in fact there is none.)
An ultrasound scan which measures the thickness of the fluid at the back of the baby’s neck (nuchal translucency) between 11 and 13 weeks is also used to screen for Down Syndrome. This is 70% accurate and has a 5% false positive rate.
You are also able to combine the ultrasound and the basic blood tests which makes the end result 85% accurate.
An example of “acting on” a screening test would be proceeding to have a diagnostic test. These tests give you a certain answer. The one that is most commonly done is called an amniocentesis. This is when a needle is put into the womb and fluid from around the baby (amniotic fluid) is extracted and sent for genetic testing. The result will tell you whether the baby does or doesn’t have a chromosomal condition. This test does however come with the risk of miscarriage which is about 1% (1 in 100 amniocenteses miscarry).
Most of these tests are done in the first trimester so it is important that you discuss this at your first antenatal visit so that you don’t miss the opportunity to do testing if it is your preference to do so.
As a compassionate care practitioner, I empathize with the challenges faced when life doesn’t go “according to (our) plan”. As a father of children with a disability, I am also sure that treasure can be found where there is trial, and that there is ALWAYS hope.