When it comes to tests you might have during pregnancy, it’s important to understand that some are screening tests, while others are diagnostic tests.
Screening tests can tell you whether there is an increased or decreased chance of something happening. Diagnostic tests, on the other hand, give definitive answers about the presence or absence of a certain condition.
Non-invasive prenatal screening (NIPS) is a screening test. Because of this, in the unlikely event you get a positive result, you will be offered a diagnostic test to confirm or rule out a diagnosis.
There are two types of diagnostic tests available for chromosome conditions. Chorionic villus sampling (CVS) can be done during the first trimester and amniocentesis can be done during the second trimester.
Both CVS and amniocentesis are invasive procedures that carry small risks, including miscarriage. That is why many women opt to first undergo a screening test to see if there is an increased chance of a condition which can then be confirmed with a diagnostic test.