Follicle-stimulating hormone (FSH) is produced by the anterior pituitary gland and is one of the two primary gonadotropins regulating reproductive function. In women, FSH drives the development of ovarian follicles during the early phase of the menstrual cycle and stimulates oestrogen production. A surge of FSH and LH triggers ovulation at mid-cycle.

In men, FSH acts on the Sertoli cells of the testes to support spermatogenesis. FSH levels are regulated by a negative feedback loop involving oestradiol and inhibin B in women, and inhibin B in men. Rising FSH in women signals that fewer responsive follicles remain, making it a valuable marker of ovarian reserve alongside AMH. In both sexes, abnormal FSH can indicate problems at the level of the pituitary or the gonads.