<prompt> The most common cause of ambiguous genitalia in a newborn is21 hydroxylase deficinece11 β hydroxylase deficiency17 α hydroxyalse deficiency3 β hydroxysteroid deficiency  <response>: 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. 