Follicle-Stimulating Hormone (FSH)

Follicle-stimulating hormone (FSH) is produced by the pituitary gland and is essential for stimulating the growth and maturation of ovarian follicles that contain developing eggs. In PCOS, FSH levels are relatively low compared to LH, creating an abnormal ratio that prevents follicles from fully maturing—the low FSH fails to adequately support follicle development while elevated LH drives androgen overproduction, resulting in multiple small follicles that stall before reaching maturity. This FSH insufficiency relative to LH is a fundamental mechanism behind PCOS-related anovulation and is the reason why fertility treatments often involve FSH supplementation.