A 39 year old woman has not had her period for 10months. She feels well but is anxious as her mother had an early menopause. Choose the single most appropriate initial investigation?

The key is B. Serum FSH/LH [here serum oestrogen is also important as i) low oestrogen + low FSH +

low LH suggest hypothalamic amenorrhoea and i) low oestrogen + high FSH + high LH suggest premature

ovarian failure! So the main determinant is serum FSH/LH. Likely cause here is premature ovarian

failure].