The anogenital ratio can be used to screen newborn female infants for fetal virilization with androgen-induced labioscrotal fusion. It applies to both premature and full-term female infants and is independent of body size.



(1) distance from anus to the base of the clitoris

(2) distance from anus to the fourchette

(3) distance from the fourchette to the base of the clitoris


anogenital ratio =

= (distance from anus to fourchette) / (distance from anus to base of clitoris)



• The mean ratio for newborn infants is 0.37 with +/- 0.07

• A ratio > 0.50 exceeds the 95% confidence limits. This suggests labioscrotal fusion and indicates the need for further evaluation.


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