Paediatricsniche
A 15-year-old girl has never had a period. Her breasts and pubic hair have been fully developed and unchanged for about a year, and she has grown 1 cm in the past twelve months after a growth spurt at 12. She is 165 cm tall. She has no headaches, no visual disturbance and no nipple discharge, and has never been sexually active. The external genitalia look normal and the vagina admits only the tip of a swab. Which one of the following investigations will be most informative?