FSH, or Follicle-Stimulating Hormone, is a hormone produced and released by the pituitary gland. Classified as a gonadotropin, FSH acts directly on the gonads—the ovaries in females and the testes in males—to regulate reproductive function and sexual development. The levels of this hormone fluctuate significantly throughout a person’s life, shifting dramatically with age and reproductive status. Understanding typical FSH values at different life stages provides context for assessing reproductive health and diagnosing hormonal conditions.
The Physiological Role of Follicle-Stimulating Hormone
FSH is a core component of the hypothalamic-pituitary-gonadal axis. The hypothalamus releases Gonadotropin-Releasing Hormone (GnRH), prompting the pituitary gland to secrete both FSH and Luteinizing Hormone (LH). This feedback loop ensures that hormone production is precisely calibrated to the body’s needs.
In females, FSH primarily targets the granulosa cells within the ovarian follicles, stimulating their growth and maturation. As these follicles develop, they begin to produce estrogen, which then acts as a negative feedback signal to the pituitary. This mechanism is responsible for selecting the dominant follicle that will ultimately release an egg during ovulation.
FSH serves a distinct purpose in males by acting on the Sertoli cells located within the testes. These cells are essential for supporting and nourishing developing sperm cells, a process called spermatogenesis. Alongside testosterone, FSH is required to maintain a healthy sperm count.
Measuring FSH levels is a common practice in clinical settings. The test is frequently used to evaluate fertility concerns, assess pituitary function, and help determine the onset of perimenopause or menopause.
FSH Reference Ranges in Females by Life Stage
FSH levels in females are highly dynamic, changing from very low values in childhood to extremely high values after the reproductive years. In prepubertal girls, FSH levels are typically suppressed, often remaining below 4.0 mIU/mL. The initial rise in FSH, often alongside LH, signals the beginning of puberty and triggers the development of secondary sexual characteristics.
During the reproductive years, the timing of the blood test within the menstrual cycle is important for accurate interpretation. FSH is generally measured on day two or three of the cycle, as this follicular phase provides a baseline assessment of ovarian function. A normal follicular phase FSH level typically falls within a range of approximately 1.4 to 9.9 mIU/mL.
FSH levels experience a brief surge around the middle of the cycle, which helps trigger ovulation. During this ovulatory peak, values can temporarily rise to a range of 6.2 to 17.2 mIU/mL or higher. Following ovulation, during the luteal phase, FSH levels drop back down, usually settling between 1.1 and 9.2 mIU/mL.
Follicular phase FSH is often used to estimate ovarian reserve. Levels consistently above 10 mIU/mL on cycle day three may suggest diminished ovarian reserve, indicating that the ovaries are less responsive and require more hormonal stimulation from the pituitary.
The most dramatic change occurs during the transition into and through menopause. As the ovarian reserve is depleted, the follicles no longer produce sufficient estrogen and inhibin to suppress the pituitary gland. This lack of feedback causes the pituitary to work harder, increasing FSH levels. In the postmenopausal stage, FSH levels stabilize at a high range, typically between 25.8 and 134.8 mIU/mL. This sustained elevation reflects the final stage of ovarian decline and identifies the menopausal transition.
FSH Levels in Males and Prepubescent Children
Unlike the fluctuating levels seen in menstruating females, FSH levels in adult males remain relatively stable. The typical range for adult men is approximately 1.4 to 15.4 mIU/mL, though variations exist between laboratories. Testing FSH in men is usually performed when evaluating male factor infertility or suspected pituitary dysfunction.
In both boys and girls before the onset of puberty, FSH levels are generally very low, reflecting the inactive state of the reproductive axis. Values are often in the range of 0 to 5.0 mIU/mL. These low levels are a result of the suppressed activity of the hypothalamus and pituitary gland during childhood.
If FSH levels begin to rise prematurely in a child, it can signal precocious puberty, where sexual development starts earlier than expected. Conversely, a failure of FSH to rise around the typical pubertal age may indicate a delay in sexual maturation. Therefore, FSH testing helps to assess the timing and progression of the body’s natural developmental schedule.
Interpreting Deviations from Normal FSH Levels
A high FSH level suggests that the pituitary is trying to stimulate the ovaries or testes, but the target organs are not responding adequately. This is most commonly seen in females as a sign of primary ovarian insufficiency, including menopause or premature ovarian failure. In males, elevated FSH levels usually point to primary testicular failure. In both sexes, high FSH is a sign that the gonadal feedback signal is weak or absent.
Conversely, an abnormally low FSH level suggests a problem originating higher up in the regulatory axis, specifically the pituitary gland or the hypothalamus. If both FSH and LH levels are low, this points toward a secondary condition, such as pituitary or hypothalamic dysfunction, which impairs the production of the stimulating hormones. Low FSH in this context can lead to a lack of ovulation in women or reduced sperm production in men.
FSH levels are not interpreted in isolation, and various external factors, such as diet, can temporarily affect a result. The use of hormonal birth control or recent illness can skew a single test result. For this reason, FSH testing is often performed alongside other hormone tests, such as Luteinizing Hormone (LH) and Estradiol, to provide a comprehensive picture of reproductive health.