Maternal peripheral testosterone levels during the first half of pregnancy.

Peripheral serum testosterone levels were determined in 180 women during weeks 7 to 20 of pregnancy with a specific radioimmunoassay. After a normal pregnancy and delivery 90 serum samples were randomly selected from mothers of boys and 90 serum samples from mothers of girls. The testosterone concentrations were correlated with the sex of the fetuses. The mean testosterone level +/- S.D. in pregnant women with female fetuses was 597 +/- 167 pg. per milliliter. In pregnant women with male fetuses the testosterone concentrations were on the average significantly higher (p less than 0.01), with a mean value of 828 +/- 298 pg. per milliliter. The course of the testosterone concentrations in women with male fetuses showed an increase beginning in week 7, reaching a maximum during weeks 9 to 11, followed by a decrease until weeks 15 to 20. During weeks 9 to 11 of pregnancy fetal sex determination was possible in 28 per cent of the males and in 5 per cent of the females, with a probability of 95.5 per cent.