Follicle stimulating hormone, FSH

An FSH test measures levels of follicle-stimulating hormone. FSH is a reproductive hormone produced by the pituitary gland. In women, it helps the ovaries grow follicles and supports estrogen production. In men, it helps support sperm production.

FSH levels can help doctors understand how the ovaries or testes are functioning. In women, FSH is often used to evaluate menstrual cycle changes, fertility concerns, ovarian reserve, and the menopausal transition. As ovarian function declines with age, the pituitary gland often produces more FSH to stimulate the ovaries.

🔍 What is a normal FSH level?

• Reproductive age: Usually under 10 IU/L in the early follicular phase.
• Borderline or elevated: Around 10–20 IU/L.
• Menopausal transition: Often above 20–25 IU/L.
• After menopause: Often above 25–40 IU/L.

FSH levels change throughout the menstrual cycle, so in women of reproductive age the test is usually done on days 2–5 of the cycle. It is often measured together with estradiol, AMH, LH, or other reproductive hormones.

A higher FSH level may suggest that the ovaries need stronger stimulation to maintain normal function. This can be associated with reduced ovarian reserve or the menopausal transition. However, FSH should not be interpreted alone. It is most useful when assessed together with age, symptoms, menstrual cycle pattern, estradiol, AMH, and previous test results.