Development of fetal male gender: prenatal sonographic measurement of the scrotum and evaluation of testicular descent.

The study was conducted to construct a centile chart of fetal scrotal size and to determine gestational age at testicular descent. A prospective, cross-sectional study was performed on 210 fetuses of normal, singleton pregnancies between 14 and 37 weeks' gestation. Scrotal circumference was measured by transvaginal ultrasonography and abdominal ultrasound between 14 and 17 weeks' and 18 and 35 weeks' gestation, respectively. The regression equation for scrotal circumference (SC) modelled as a function of gestational age (GA) was: SC (mm) = exp (1.05 + 0.09 GA (weeks)) The correlation r = 0.96 was found to be highly statistically significant (p < 0.0001). The prediction of scrotal circumference per week and the 95% confidence interval (CI) were defined. Testicular descent was not observed prior to 2.5 weeks' gestation, with 30% of the fetuses having one or both testes descended at 25 weeks (p < 0.001) and 97% after 32 weeks. The presented normative data may be helpful in the prenatal diagnosis of suspected congenital syndromes that include, among their manifestations, scrotal abnormalities and early detection of cryptorchidism.