This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pediatrics
Pseudo hermaphroditism in a female child is most commonly due to: 
Select and explain. 
A. 21-hydroxylase deficiency, B. 17-hydroxylase deficiency, C. 11-hydroxylase deficiency, D. 3-hydroxylase deficiency
A: 21-hydroxylase deficiency
Answer: A: 21-hydroxylase deficiency 
Explanation: a. 21-hydroxylase deficiency(Ref: Nelson's 20/e p 2714-2723, Ghai 8/e p 526-527)Classic 21-hydroxylase deficiency is the most common cause of ambiguous genitalia in a female newborn. Virilization is usually apparent at birth in females, i.e. Pseudo hermaphroditism of a female child.