THE EFFECT OF FETAL GENDER ON THE PREDICTION OF DOWN-SYNDROME BY MEANS OF MATERNAL SERUM ALPHA-FETOPROTEIN AND ULTRASONOGRAPHIC PARAMETERS

OBJECTIVE: Our investigation was designed to use maternal serum alpha- fetoprotein and individual or combinations of ultrasonographic paramet ers to examine the influence of fetal gender on the prediction of Down syndrome. STUDY DESIGN: A cohort study of 5114 patients who underwent karyotype analysis between 13 and 22 weeks' gestation was undertaken. Maternal demographic variables, anthropometric indices, and maternal serum alpha-fetoprotein values were assessed. Fetal parameters recorde d included gender, biparietal diameter, head circumference, femoral an d humeral length, transverse cerebellar diameter, and nuchal fold thic kness. The effect of fetal gender on maternal serum alpha-fetoprotein values and ultrasonographic parameters was assessed. Gender-specific d ifferences between fetuses with Down syndrome and euploid fetuses were identified, and the optimal cutoff values of individual and combinati ons of biometric parameters were determined by receiver operating char acteristic curve analysis. RESULTS: A total of 42 fetuses with Down sy ndrome were identified. Female fetuses with Down syndrome had signific antly lower maternal serum alpha-fetoprotein values than their male co unterparts, and maternal serum a-fetoprotein screening paradigms resul ted in the disproportionate identification of affected female fetuses. A nuchal fold thickness greater-than-or-equal-to 5 mm was the single best ultrasonographic predictor of Down syndrome independent of fetal gender. Affected male fetuses had significantly smaller mean femoral a nd humeral lengths than euploid fetuses after adjustment for biparieta l diameter, but only the humeral length proved a clinically useful pre dictor of Down syndrome. Pearson's correlation coefficient confirmed t hat nuchal fold thickness and humeral length were independent of each other and of maternal age and maternal serum alpha-fetoprotein levels. The optimal ultrasonographic predictor of Down syndrome was the prese nce of either a nuchal fold thickness greater-than-or-equal-to 6 mm or a humeral length > 3.5 to 3.7 mm below the expected value. This combi nation of ultrasonographic findings identified 41.7% of female and 66. 7% of male fetuses with Down syndrome. CONCLUSIONS: Fetal gender affec ts the prediction of Down syndrome by both maternal serum alpha-fetopr otein and ultrasonographic parameters. Moreover, the ultrasonographic detection of Down syndrome in fetuses is greatly improved by a combina tion of gender-specific biometric parameters.