MATERNAL SERUM HUMAN CHORIONIC-GONADOTROPIN AND PREGNANCY-ASSOCIATED PLASMA PROTEIN-A, MARKERS FOR FETAL DOWN-SYNDROME AT 8-14 WEEKS

Maternal serum levels of human chorionic gonadotrophin and its subunits (intact, alpha, and free betahCG) and pregnancy-associated plasma protein A (PAPP-A) were measured in 279 women between 8 and 14 weeks' gestation. This group included 23 pregnancies in which the fetus had Down syndrome (DS), diagnosed either at birth or during the second trimester (n = 17) or from chorionic villus sampling (CVS) (n = 6). Normal medians were determined from the 258 apparently normal pregnancies. The median levels of intact hCG (1.4 MOM) and free betahCG (2.1 MOM) were significantly raised, whereas the median level of PAPP-A (0.39 MOM) was significantly lower in the DS pregnancies when compared with the control group. Levels of alphahCG were similar in both the control and the DS pregnancies. Analysis of samples taken prior to 14 weeks' gestation demonstrated that only PAPP-A (0.34 MOM) was significantly altered in DS pregnancies. However, after the exclusion of DS cases diagnosed at CVS, the median intact hCG (1.56 MOM), free betahCG (2-27 MOM), and alphahCG (1.8 MOM) were all raised in DS pregnancies. This emphasizes the problem of the interpretation of biochemical markers when DS cases are diagnosed at CVS.