IS MATERNAL SERUM TRIPLE SCREENING A BETTER PREDICTOR OF DOWN-SYNDROME IN FEMALE THAN IN MALE FETUSES

Among euploid gestations, female fetuses have been reported to have si gnificantly 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 independen tly 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 containi ng all karyotypes from amniocentesis performed between August 1994 and August 1996 was accessed. All trisomy 21 cases were identified. The m ale-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 mater nal age (AMA), which served as the control group. Statistical analysis utilized chi-square, Fisher's exact test, and Student's t-test. A P v alue of less than 0.05 was considered statistically significant. Forty -nine trisomy 21 fetuses were detected in the women who underwent amni ocentesis because of abnormal triple screening and 311 were detected i n the control group. The proportion of male fetuses among the triple s creening group was not significantly different from that of the AMA gr oup (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 r atio (alpha=0.05, beta=0.20). The reported differences in MSAFP and hC G levels between male and female euploid fetuses do not appear to affe ct the sex ratio among Down syndrome fetuses detected because of an ab normal maternal serum triple screening. (C) 1998 John Wiley & Sons, Lt d.