Follicle-stimulating hormone (FSH) is a key hormone of the reproductive system. It is responsible for ovarian follicle growth. Follicles aid in the maintenance of women's menstrual cycles by producing oestrogen and progesterone. FSH plays a role in both sperm production and gonad development in men. The FSH test calculates how much FSH is present in your blood. Your doctor might advise an FSH test to determine the underlying cause of problems affecting the reproductive system.