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Follicle-Stimulating Hormone Test, FSH

Follicle-stimulating hormone test, FSH, is a baseline test used to gauge fertility

For women having difficulty getting pregnant, one of the first tests we conduct is the follicle-stimulating hormone test, commonly known as FSH. This hormone stimulates the growth and maturation of eggs (follicles) in the ovaries during the follicular phase of the menstrual cycle in women of childbearing age.

Follicle-stimulating hormone is made by the pituitary gland, a small organ located in the center of the head behind the sinus cavity at the base of the brain. Control of FSH production is a complex system involving the hypothalamus in the brain, the pituitary gland, and the hormones produced by the ovaries or testicles. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the pituitary to release FSH and luteinizing hormone (LH), a closely related hormone also involved in reproduction.

The menstrual cycle is divided into the follicular and the luteal phases, each phase lasting about 14 days. During the follicular phase, FSH initiates the production of estradiol by the follicle, and the two hormones work together in the further development of the egg follicle. Near the end of the follicular phase, there is a surge of FSH and luteinizing hormone. Ovulation whereby the egg is released from the ovary occurs shortly after this surge of hormones.

Checking follicle-stimulating hormone levels can tell your doctor important information about your ovarian function.

As a woman ages and menopause approaches, ovarian function decreases and eventually ceases. As this occurs, FSH and LH levels rise. This is because as ovarian function decreases, the pituitary has to produce more FSH in an attempt to stimulate the ovaries to produce follicles.

For a woman, an FSH test may be ordered when she is having difficulty getting pregnant, has irregular or an absence of menstrual periods, or sometimes when it is suspected that she has entered menopause.

Elevated FSH levels may be a predictor of diminished ovarian reserve. Menopause occurs when the ovaries stop working. Menopausal women therefore have very high levels of FSH, as the pituitary makes more and more FSH in a vain attempt to get the ovaries to respond.

Follicle-stimulating hormone levels are generally checked on day 2, 3 or 4 of the patient’s menstrual cycle.

FSH levels can also be checked for men during fertility testing.

FSH is also the hormone that stimulates the testes to produce mature sperm in men. FSH level (along with other hormone tests) is performed to evaluate testicular function. The test may be ordered when his partner cannot get pregnant, when he has a low sperm count, or when he has low muscle mass or decreased sex drive, for example.

As with women, elevated FSH levels may indicate testicular failure and the inability to produce mature sperm.