The NIPS test I had says it has a sensitivity and specificity of 99%. Does that mean my risk is 99% if my screening result is positive?

No. The sensitivity and specificity refer to the ability of the test to accurately call a negative result negative, or a positive result positive. If you’re screening result is “positive” (remember, this is not a diagnosis), the risk is based on your age and the specific condition. This is because the risk for many of the conditions screened for by NIPS increases each year as a woman ages. So as a woman ages, it is more likely for a positive to be a true positive.

For example, a 21-year-old woman who has a “positive” NIPS for trisomy 13 actually has just a 6% risk that the pregnancy is actually affected. This is because trisomy 13 is a rare condition, NIPS is not as accurate for trisomy 13 as other conditions, and because of her age, her starting risk was very low.

A 35-year-old woman who has a “positive” NIPS for Down syndrome however, has a 79% chance that the condition is actually present, because her starting risk based on her age was higher, NIPS is most accurate at screening for Down syndrome, and Down syndrome is more common in the general population.