Maternal use of androgens or high doses of certain weakly androgenic synthetic progestogens (progestins) structurally related to testosterone can masculinize (virilize) the external genitalia of a female fetus during susceptible times in pregnancy.

Some degree of fusion of the labioscrotal folds and urogenital folds and clitoral enlargement can occur if exposure occurs from the 8th through the 12th week of gestation, but only clitoral enlargement can occur if exposure occurs after the 12th week. This can in some cases result in ambiguous genitalia.

Fetal masculinization of female external genitalia is usually due to enzyme abnormalities involved in adrenal steroid biosynthesis, resulting in congenital adrenal hyperplasia (CAH); fetal masculinization of female external genitalia is much less frequently due to maternal use of androgenic steroids.

Fetal masculinization of female external genitalia due to maternal use of androgenic steroids is generally less advanced than that due to CAH, and unlike CAH, does not cause progressive virilization.

Affected females mature normally with normal fertility, there is almost total regression of the genital anomaly in cases of simple clitoral enlargement, and in even the most severe cases, surgical correction of labioscrotal fusion is relatively simple.