Does an abnormal or positive prenatal screen result mean that my baby will have Down syndrome?
Prenatal screening, including a ‘triple screen’, ‘quad screen’ or ‘integrated screen’, are screening tests which are different than diagnostic tests. A screening test tells you the chance of a particular outcome (e.g. that your baby will have Down syndrome) whereas a diagnostic test is able to tell you definitively whether or not a particular outcome will occur.
Let’s think about an abnormal or positive prenatal screen result for Down syndrome. Since this test is about chances, your result is usually described as a fraction. For example, you may be told that there is a 1/5 chance that the baby has Down syndrome. This means that there is a 1 in 5 (or 20%) chance that the baby will have Down syndrome. You may ‘flip’ this chance around and see that there is a 4 in 5 (or 80%) chance that the baby will not have Down syndrome.
If your chance is high enough, you may be offered the option of further diagnostic testing. These tests (e.g. chorionic villus sampling, amniocentesis) will provide you with a definitive result. One reason that these diagnostic tests are not offered to every woman is that there is a chance of miscarriage (about 1 in 200) associated with these procedures.
Receiving an abnormal or positive test result can be confusing and stressful so it’s important to discuss the results with your health care provider.