Changes in maternal serum total and free androgen levels in early pregnancy: lack of correlation with fetal sex.

The fetal testis actively produces androgens during early gestation. To determine whether this fetal production of androgens might be reflected by levels of androgens in maternal serum, which might then be a useful test for antenatal fetal sex determination, we measured serum testosterone (total and free) and serum dihydrotestosterone in 83 pregnant women whose fetuses ranged from 4 to 20 weeks in age. For no maternal serum androgen measured was there a significant difference between women carrying a male fetus and those carrying a female fetus, even when this comparison was limited to various 4-week subintervals or fetal age. Total serum testosterone correlated directly with fetal age (r = 0.341, p less than 0.005), but serum dihydrotestosterone did not (r = 0.146, p = NS). Inverse correlations with fetal age were observed for percentage free testosterone (r = -0.531, p less than 0.001) as well as absolute serum free testosterone (r = -0.349, p less than 0.005). We conclude that maternal serum androgen levels are not useful for antenatal fetal sex determination in early pregnancy. The reason for the progressive fall in serum free testosterone, and presumably androgen production, during early gestation remains obscure.