This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
In child with ambiguous genitalia, first test to be done is 
Select and explain. 
A. Serum 17 hydroxy progesterone, B. Karyotyping, C. Serum 17 ketosteroid, D. Ultra sound pelvis
B: Karyotyping
Answer: B: Karyotyping 
Explanation: Karyotyping is first test to be done in child with ambiguous genitalia.