First Trimester Aneuploidy Screening Using Nuchal Iranslucency, Free Beta Human Chorionic Gonadotrophin and Maternal Age

Summary: Screening for aneuploidy using maternal age has a low detection rate and high false positive rate. Second trimester maternal serum screening increases trisomy 21 detection and decreases die false positive rate. First trimester screening would enable definitive diagnosis with chorionic villus sampling, and simple surgical termination of affected pregnancies would still be an option. Nuchal translucency (NT), free beta human chorionic gonadotrophin (fβHCG) and maternal age were assessed in 302 patients before chorionic villus sampling. NT positively and fβHCG negatively correlated with gestation, but neither correlated with maternal age nor with each other. Both NT and fβHCG were increased in trisomy 21. NT was increased and fβHCG was decreased in trisomy 18. Multivariate discriminant analysis enabled 87.5% detection of trisomy 21 in this high-risk population, for a 14% false positive rate. In a simulated normal population, using a risk cut-off of 1 in 250, 71% detection was achieved for a 7% false positive rate. The combination of NT, fβHCG and maternal age is a simple, readily available and viable first trimester screening strategy.