FSH (Follicle-Stimulating Hormone)

FSH is released by the pituitary gland and acts on the gonads. In women, FSH recruits and stimulates growth of ovarian follicles at the start of each menstrual cycle. In men, FSH supports sperm production in the seminiferous tubules of the testes.

A baseline day-3 FSH blood test is used to assess ovarian reserve in women. As the ovarian reserve diminishes, the pituitary must produce more FSH to recruit follicles, so elevated FSH (typically above 10 IU/L) suggests reduced reserve. FSH is also a key ingredient in injectable gonadotropin medications used for ovarian stimulation in IVF and IUI cycles.