Follicle-Stimulating Hormone

In Depth

Follicle-Stimulating Hormone (FSH) is a gonadotropin released by the pituitary gland in the brain. Its primary function in women is to stimulate the growth and maturation of ovarian follicles—the tiny sacs within the ovaries that contain eggs and produce hormones. As ovarian follicles mature, they release estrogen.

During perimenopause, as the number of viable ovarian follicles decreases, the pituitary gland must release more FSH to try and stimulate the ovaries. This leads to a gradual rise in FSH levels. In natural menopause, FSH levels typically rise significantly, often above 30-40 mIU/mL, and remain elevated. This elevated FSH is a key diagnostic marker used by healthcare providers to confirm the menopausal transition, especially when menstrual cycles become irregular or cease. High FSH levels indicate that the ovaries are no longer responding robustly to the pituitary's signals, signifying diminished ovarian reserve.

The rise in FSH is part of the feedback loop that governs the reproductive system. When estrogen and inhibin (a hormone produced by the follicles) levels drop, the pituitary gland senses this and increases FSH production. Conversely, when estrogen levels are high, FSH production is suppressed. This dynamic interplay is disrupted as ovarian function declines. Monitoring FSH can help track the progression of the menopause transition, though it's important to note that FSH levels can fluctuate significantly during perimenopause, making a single reading less definitive than during established postmenopause.

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