Follicle-stimulating hormone (FSH) helps control a woman's menstrual cycle and egg production and also a man's sperm production. FSH is produced by the pituitary gland.
Women's FSH levels normally vary throughout the menstrual cycle and are highest just before release of an egg (ovulation). Men's FSH levels normally stay at a constant level. An abnormally high or low level of FSH is often a sign of an inability to produce eggs or sperm.