The first-trimester screen in clinical practice.

The first-trimester screen combines nuchal translucency measurement and serum levels ot PAPP-A and beta-hCG between 11 and 13 weeks gestational age which can be used to calculate the risk of fetal Trisomy 21 and 18. Although these trisomies are the most common conditions detected, recognition of increased risk for several other fetal conditions and maternal complications have also been documented. A common misconception is that requesting this test implies that the patient will automatically terminate an affected fetus.