The Follicle Stimulating Hormone (FSH) test is a blood test that measures the level of FSH, a key reproductive hormone made by the pituitary gland (a small gland at the base of the brain). FSH helps control the function of the ovaries in women and the testes in men.

In people with ovaries, FSH stimulates the growth of ovarian follicles (which contain eggs) and supports estrogen production. Because the body often makes more FSH when the ovaries are not responding well, FSH is commonly used as part of an evaluation of ovarian reserve and menopausal transition. In general:

Higher FSH in an adult with ovaries may suggest decreased ovarian reserve or reduced ovarian function (such as during the transition to menopause or with primary ovarian insufficiency). Lower FSH may suggest that the pituitary or hypothalamus is not sending enough hormonal signals to the ovaries.

In people with testes, FSH stimulates sperm production (spermatogenesis) by acting on the Sertoli cells. When the testes are not functioning well, the pituitary may increase FSH, so:

Higher FSH may point toward impaired sperm production (testicular failure). Lower FSH may suggest a signaling problem from the brain (pituitary or hypothalamus).

FSH levels naturally vary by age, sex, and—if you menstruate—by the timing of your menstrual cycle. Many clinicians interpret FSH alongside related labs such as LH (luteinizing hormone), estradiol, AMH (anti-Müllerian hormone), testosterone, and prolactin, as well as symptoms and medical history.

A clinician may order an FSH test to help evaluate fertility, menstrual cycle changes, signs of menopause, or causes of abnormal puberty. It is also commonly included in a work-up for hormonal imbalance or reproductive endocrine conditions.

In women and people who menstruate, FSH is often checked when there are:

Irregular, infrequent, or absent periods (amenorrhea)

Difficulty getting pregnant or concern about ovarian reserve (fertility evaluation)

Symptoms suggesting perimenopause or menopause, such as hot flashes, night sweats, vaginal dryness, sleep disruption, or mood changes

Suspected primary ovarian insufficiency (early loss of ovarian function) or early menopause

Concern for polycystic ovary syndrome (PCOS) or other ovulation disorders (often interpreted with LH, androgens, and ultrasound findings)

In men and people with testes, FSH may be ordered for:

Infertility evaluation (especially low sperm count or poor sperm quality)

Small testicular size, low testosterone symptoms, or suspected testicular dysfunction

Evaluation of pituitary disorders that can affect reproductive hormones

In children and adolescents, FSH can help assess:

Early puberty (precocious puberty) or delayed puberty

Possible pituitary or gonadal (ovary/testis) disorders affecting development

Timing note: For ovarian reserve testing, FSH is commonly measured early in the menstrual cycle (often around day 3), because levels change across the cycle. Your clinician will advise the best timing and which companion tests are most useful for your situation.

• Menopause and perimenopause
• Primary ovarian insufficiency (premature ovarian failure)
• Diminished ovarian reserve (reduced egg quantity/quality)
• Polycystic ovary syndrome (PCOS) and ovulatory dysfunction (interpreted with other hormones)
• Pituitary disorders (e.g., hypopituitarism, pituitary adenoma affecting gonadotropins)
• Hypothalamic dysfunction (e.g., functional hypothalamic amenorrhea)
• Primary testicular failure (impaired spermatogenesis)
• Genetic or chromosomal conditions affecting gonadal function (e.g., Turner syndrome, Klinefelter syndrome)
• Precocious puberty or delayed puberty

• Fertility planning and reproductive health assessment (including ovarian reserve and sperm production evaluation)
• Clarifying menopause status and guiding symptom management discussions
• Identifying causes of irregular or absent periods to support cycle regulation goals
• Hormone balance evaluation as part of an endocrine check-up (with LH, estradiol/testosterone, prolactin, thyroid tests when appropriate)
• Monitoring recovery or function after treatments that may affect ovaries or testes (e.g., chemotherapy/radiation), when recommended by a clinician
• Assessing pubertal development concerns in adolescents (early or delayed puberty evaluation)