<prompt> The most common cause of ambiguous genitalia in a newborn is -21 hydroxylase deficinece11 beta - hydroxylase deficiency17 alpha - hydroxyalse deficiency3 beta - hydroxysteroid deficiency  <response>: Ans. is a i.e., 21 hydroxylase deficiency o Congenital adrenal hyperplasia due to classic 21-Hydroxylase deficiency is the most common cause of ambiguous genitalia in the newborn. Virilization is apparent at bih in the female and within the first 2-3 years of life in the male. 