Follicle-stimulating hormone (FSH) is a hormone made by the pituitary gland, a small gland at the base of the brain. In women, FSH helps control the menstrual cycle and the growth of eggs in the ovaries. In men, it supports sperm production. This test measures the amount of FSH in the blood. This test is used to help evaluate fertility, menstrual cycle problems, and the function of the ovaries or testicles. It can help assess whether a woman has entered menopause and can help investigate causes of low sperm count or infertility. It is also used to look at pituitary gland function and, in children, to evaluate early or delayed puberty.