The most common cause of ambiguous genitalia in a newborn is –
Congenital adrenal hyperplasia due to classic 21-Hydroxylase deficiency is the most common cause of ambiguous genitalia in the newborn. Virilization is apparent at birth in the female and within the first 2-3 years of life in the male.
21 hydroxylase deficinece
11 β – hydroxylase deficiency
17 α – hydroxyalse deficiency
3 β – hydroxysteroid deficiency