Amniotic fluid testosterone and fetal sex determination (discussion of the endocrine function of the fetal testis).

Amniotic fluid testosterone levels were determined by the radioimmunoassay technique in 101 samples obtained by amniocentesis between 16 and 18 weeks of gestation from women with increased risk of chromosomal abnormalities. Fetal sex was determined by cell culture and chromosomal analysis of fetal amniotic cells and was confirmed at birth. In pregnancies with male fetuses (50 samples), the mean amniotic fluid testosterone level of 216 pg/ml (+/- 75) was significantly higher (p less than 0.001) than the mean value of 93 pg/ml (+/- 28) found in pregnancies with female fetuses (51 samples). The range for pregnancies with male fetuses was 130 to 500 pg/ml and for those with female fetuses 10 to 140 pg/ml, showing an area of overlap from 130 to 140 pg/ml.