A 34-year-old G3P2 delivers a baby by spontaneous vaginal delivery. She had scant prenatal care and no ultrasound, so she is anxious to know the sex of the baby. At first glance you notice female genitalia, but on closer examination the genitalia are ambiguous.
Which of the following is the best next step in the evaluation of this neonate?
A. Chromosomal analysisAmbiguous genitalia at birth is a medical emergency, not only for psychological reasons for the parents, but also because hirsute female infants with congenital adrenal hyperplasia (CAH) may die if undiagnosed. CAH is an autosomally inherited disease of adrenal failure that causes hyponatremia and hyperkalemia due to lack of mineralocorticoids. A thorough physical examination is the best initial evaluation. While it will not provide the definitive diagnosis of the gender, it can provide clues. Examination should include inspection and palpation of the genitalia, palpation for gonads in the inguinal canal or labioscrotal folds, evaluation for fused labia, evaluation for presence of a vagina or pouch, and assessment for other nongenital dysmorphic features. The newborn should also be quickly evaluated for presence of hyper- or hypotension, or signs of dehydration. Karyotype, electrolyte analysis, blood or urine assays for progesterone, 17a-hydroxyprogesterone, and serum androgens such as dehydroepiandrosterone sulfate are essential to the workup as well. Pelvic ultrasound or MRI can detect ovaries or undescended testes, but that is not the first step in management. Laparotomy or laparoscopy is sometimes necessary for ectopic gonadectomy after puberty has occurred.