How accurate is NIPT?

This question has two different answers, and the difference matters enormously to you personally. Laboratories quote detection rate and false positive rate. These are high, and they are what makes NIPT better than older screening tests. But they describe how the test performs across a whole population. What matters to you is the positive predictive value — if your result comes back high-risk, what is the chance your baby actually has the condition? That figure is often much lower than people expect, and it depends heavily on how common the condition is. ACMG puts it directly: the negative predictive value can be considered high, but the positive predictive value is not as desirable, because Down syndrome is relatively uncommon across the age range of women giving birth — around 0.6% at second-trimester amniocentesis. A truly diagnostic test would have predictive values approaching 100%. NIPT does not. In practical terms: a low-risk result is very reassuring. A high-risk result means your chance is increased, but it is not a diagnosis, and a substantial proportion of high-risk results turn out to be unaffected pregnancies. This is why confirmatory testing by CVS or amniocentesis is recommended after a high-risk result, and why you should ask for the positive predictive value for your specific result and your age — not the general accuracy figure from the brochure.