First-Trimester or Second-Trimester Screening, or Both, for Down’s Syndrome

Debate continues over whether to screen pregnant women for fetal Down syndrome in the first or the second trimester of pregnancy or in both trimesters. The First- and Second-Trimester Evaluation of Risk Factors (FASTER) Trial obtained direct comparative data on current screening methods from 38,167 women with singleton pregnancies who were cared for at 15 U.S. centers over approximately 3 years in 1999–2002. Down syndrome was found in 117 instances. Inclusion criteria included a maternal age of 16 or older and a fetal crown-rump length of 36 to 79 mm—consistent with a gestational age of 10 weeks 3 days through 13 weeks 6 days. First-trimester screening combined measurement of the nuchal translucency with maternal serum pregnancy-associated plasma protein A (PAPP-A) and free beta human chorionic gonadotropin (fhCG) levels. Quadruple screening in the second trimester, from 15 to 18 weeks gestation, included alpha-fetoprotein, total hCG, unconjugated estriol, and inhibin. Stepwise sequential screening, in which the Down syndrome risk estimate was provided after each test, was compared with “fully integrated” screening, which yielded only a single risk result after both the first- and second-trimester screening tests had been done.