Sex-related differences in the development of the human fetal corpus callosum: in utero ultrasonographic study.

A cross-sectional study of pregnant women presenting for routine fetal ultrasonographic examination was conducted at the Obstetric Ultrasonographic Unit of the Chaim Sheba Medical Center to investigate in utero development of the fetal corpus callosum (CC) in relation to fetal gender. A total of 255 consecutive healthy fetuses of low-risk pregnancies between 16 and 36 weeks' gestation were examined. Thickness and width of the anterior mid-body of the CC were measured in the mid-coronal plane, and length was measured in the mid-sagittal plane. Fetal gender was determined by an independent observer. Female fetuses had statistically significantly thicker CC than males for each gestational age. The mean +/- standard deviation (SD) CC thickness in females was 2.13 +/- 0.8 mm [95% confidence interval (CI) 1.98-2.28] while the mean +/- SD CC thickness in males was 1.8 +/- 0.5 mm (95% CI 1.70-1.89; p < 0.01). The length and width of the CC during gestation did not differ significantly between the sexes. Corpus callosum size as a function of gestational age (GA) in both sexes was expressed by linear regression equations. The correlation coefficients r = 0.93, r = 0.61 and r = 0.62 for length, width and thickness, respectively, in males and r = 0.92, r = 0.71 and r = 0.72 in females were found to be statistically significant (p < 0.01). The present data suggest that female fetuses have a thicker CC than males. These findings support previous studies suggesting sex dimorphism of human CC and raise the possibility that prenatal sex hormones may play a role in determining callosal development.