What is the difference between a screening test and a diagnostic test?

A screening test (NIPS, first trimester screening, maternal serum screening) adjusts a woman’s risk to have a pregnancy affected with a specific condition based on certain factors. The result will either increase or decrease the risk for those specific conditions.

A diagnostic test looks directly at the baby’s genetic information to give a yes or no answer as to whether or not a baby is affected by a specific condition. A diagnostic test is the only way to know for sure whether or not a baby is affected during a pregnancy. However, starting with a screening test may help a woman decide if a diagnostic test during a pregnancy is necessary.