Is maternal serum triple screening a better predictor of Down syndrome in female than in male fetuses?

Abstract

Among euploid gestations, female fetuses have been reported to have significantly lower maternal serum alpha-fetoprotein (MSAFP) and higher human chorionic gonadotropin (hCG) levels than male fetuses. Since in maternal serum triple screening, low MSAFP and high hCG MOM independently confer greater risk of a Down syndrome fetus, we investigated the hypothesis that maternal serum triple screening is more efficacious at detecting female than male Down syndrome fetuses. A database containing all karyotypes from amniocentesis performed between August 1994 and August 1996 was accessed. All trisomy 21 cases were identified. The male-to-female ratio among trisomy 21 fetuses detected at amniocentesis after abnormal maternal serum triple screening was compared with that among trisomy 21 fetuses detected at amniocentesis for advanced maternal age (AMA), which served as the control group. Statistical analysis utilized chi-square, Fisher's exact test, and Student's t-test. A P value of less than 0.05 was considered statistically significant. Forty-nine trisomy 21 fetuses were detected in the women who underwent amniocentesis because of abnormal triple screening and 311 were detected in the control group. The proportion of male fetuses among the triple screening group was not significantly different from that of the AMA group (55 per cent vs. 57 per cent; P=0.9). Our study had a power of 80 per cent to detect a difference of 25 per cent in the male-to-female ratio (alpha=0.05, beta=0.20). The reported differences in MSAFP and hCG levels between male and female euploid fetuses do not appear to affect the sex ratio among Down syndrome fetuses detected because of an abnormal maternal serum triple screening.