This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sex Intersexuality, Subject name: Gynaecology & Obstetrics
[{'content': 'An infant is found to have clitoral enlargement and some degree of labial fusion. What is the first step in arriving at a diagnosis? \nSelect and explain. \nA. Perform a karyotype, B. Perform an ultrasound scan, C. Perform blood 17-hydroxy progesterone levels, D. Perform serum testosterone levels', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is a, i.e. Perform a karyotypeA child born with ambiguous external genitalia could be a female who has been exposed to androgens, such as in the case of congenital adrenal hyperplasia, or a true hermaphrodite, or an under masculinized male. Such a male could have 5a-reductase deficiency, or abnormal androgen receptors, or Mullerian inhibitor deficiency. Therefore, the first step in the diagnosis is to perform a karyotype, to diagnose whether the child is a male or a female, because further investigations would depend on the genetic sex. However, a true hermaphrodite could be XX or XY.', 'role': 'assistant'}]