Maternal serum α-fetoprotein, β-human chorionic gonadotropin, and unconjugated estriol levels in midtrimester trisomy 18 pregnancies

Abstract

The purpose was to evaluate the levels of maternal serum human chorionic gonadotropin, alpha-fetoprotein, and unconjugated estriol in trisomy 18 pregnancies compared with normal singleton pregnancies. Sera from 14 trisomy 18 pregnancies (13 retrospectively and one prospectively ascertained) were analyzed for human chorionic gonadotropin, alpha-fetoprotein, and unconjugated estriol. The alpha-fetoprotein levels in the 10 trisomy 18 pregnancies without open neural tube or ventral wall defect had a median of 0.65 multiple of the median, although two had alpha-fetoprotein levels above 2.5 multiples of the median. The human chorionic gonadotropin levels had a median of 0.32 multiple of the median and the unconjugated estriol levels had a median of 0.56 multiple of the median. Although most women with trisomy 18 pregnancies had serum human chorionic gonadotropin levels that were less than 1.0 multiple of the median, three had markedly elevated human chorionic gonadotropin levels (greater than 5.0 multiples of the median). Our data are partially consistent with those previously published but suggest the possibility of a bimodal distribution of alpha-fetoprotein and human chorionic gonadotropin levels in trisomy 18-affected pregnancies, unrelated to a neural tube or abdominal wall defect. The efficiency of screening for trisomy 18 prospectively, using the three serum markers, requires further evaluation.