The ultrasound estimation of sex-related variations of intrauterine growth.

The fetal ultrasound parameters of biparietal diameter, head circumference, abdominal circumference, and the product of crown-rump length and trunk area were estimated from serial measurements at 16 weeks' gestation to term in a sample of 96 pregnant European women. The slower rate of growth in the female fetus compared to that in the male fetus was statistically significant by 28 weeks' gestation, and this discrepancy increased toward term. This sex-related difference was reflected in the birth weight, head circumference, and crown-heel length of the newborn infant. The variation of intrauterine growth affected both head and abdomen equally as the head/abdominal circumference ratio did not differ significantly between the sexes throughout pregnancy and the neonatal ponderal indices were similar.