After having NIPS, you and your healthcare provider will receive a result that says either “negative” or “positive.”
A negative NIPS result indicates a low risk for a chromosome condition tested for in the pregnancy. Most people get a negative result and feel reassured, though it’s important to keep in mind that NIPS does not screen for all chromosome conditions. Only a diagnostic test — chorionic villus sampling (CVS) or amniocentesis — can provide a complete picture of the baby’s chromosomes.
A positive NIPS result indicates an increased chance for a chromosome condition in the pregnancy. The typical next step is to consider a diagnostic test (CVS or amniocentesis) to confirm or rule out a diagnosis. Before considering a diagnostic test, you’ll probably be wondering “What is the chance my pregnancy is truly affected?”
The answer to that question is a statistic that will be included in your report called the positive predictive value (PPV). This number tells you the chance that a positive result from NIPS is truly positive.
PPV depends on maternal age and gestational age of the pregnancy. So the same “positive” NIPS result can have different meanings for different women. For example, if four women (aged 25, 30, 35, and 40) all have NIPS at 10 weeks into their pregnancies, they could all get the same “positive” result for trisomy 21 (Down syndrome) but have different PPVs and therefore different chances of really having a pregnancy with trisomy 21. See the chart below.
You’ll notice that the oldest woman has the highest PPV and the youngest woman has the lowest. This is because we know that the chance of having a pregnancy with a trisomy increases with maternal age.
Your healthcare provider or a genetic counselor can help you make sure you understand everything about your results so that you can make informed decisions about your next steps, whatever those might be.