ABSTRACT
Routine multimarker screening for Down’s syndrome (DS) is now an established practice in many areas of the world. In the second trimester, the most common markers include maternal serum human chorionic gonadotropin (hCG) or its free β subunit (Fβ-hCG), α-fetoprotein (AFP) and unconjugated estriol (uE3). Large studies using combinations of hCG (or Fβ-hCG) and either or both of the other markers confirm model predictions that about twothirds of DS-affected pregnancies can be detected with a false-positive rate (FPR) of about 5%1. In the first trimester, the combination of maternal serum pregnancy-associated placental protein-A (PAPP-A) and Fβ-hCG can achieve similar performance2.
