Amniotic fluid testosterone levels in midpregnancy.

Amniotic fluid testosterone levels were measured on specimens obtained between 12 and 25 weeks' gestation from 58 male-fetus and 77 female-fetus pregnancies. For the male fetuses the mean +/- SE amniotic fluid testosterone level of 223 +/- 10 pg/ml was significantly higher (P less than 0.001) than the concentration found for the female fetuses (40 +/- 2 pg/ml). The ranges were 104-424 and 18-82 pg/ml, respectively, for the same fetuses. In the male fetuses the highest mean level was found during the 17th gestational week, but the mean level observed during any 1 week was not significantly differenf from any other week for both sexes. These data are consistent with the concept that amniotic fluid testosterone levels may be a rapid and effective method for establishing fetal sex in utero during midgestation.