Progestin-induced virilization

Maternal use of androgens or high doses of certain weakly androgenic synthetic progestogens (progestins) structurally related to testosterone can masculinize (virilize) the vulva 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.

Source: Wikipedia — Progestin-induced virilization (CC BY-SA 4.0)