Lexicon
FSH
Also known as Follicle-stimulating hormone
Definition
Follicle-stimulating hormone (FSH) is one of the gonadotropins released by the pituitary that acts on the ovarian follicles to trigger their growth as part of the hypothalamic-pituitary-ovarian axis. [1] FSH and luteinizing hormone (LH) play complementary roles in follicle development and ovulation via a complex interaction in the hypothalamus, anterior pituitary gland, reproductive organs, and oocytes. [2] FSH is a glycoprotein hormone whose glycosylation varies in functionally important ways that can modulate its affinity for and signaling through its cognate receptor. [3]
How it works
The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which triggers pituitary release of gonadotropins, namely FSH, to act on ovarian follicles and trigger their growth. [1] FSH is required for proper oocyte maturation largely through its action on granulosa cells, which are the primary producers of estradiol, and balance of the axis requires ovarian sex steroids to inhibit the release of gonadotropins from the pituitary in an endocrine feedback loop. [1] In the male, the endocrine stimulation of spermatogenesis involves both FSH and luteinizing hormone, and because germ cells lack receptors for FSH and testosterone the hormonal signals are transduced through the Sertoli cells and peritubular cells. [4] During ovarian ageing the declining cohort of antral follicles reduces the negative feedback from ovarian factors at the hypothalamo-pituitary unit, which first results in gradually elevated FSH levels followed by cycle irregularity. [5]
Connected concepts
How it's measured
FSH is measured as a serum concentration, conventionally reported in international units per litre (IU/l), alongside related reproductive markers such as estradiol, LH, inhibin, and anti-Müllerian hormone. [6] For diagnosing premature ovarian insufficiency, guidance is that a repeat FSH measurement and/or AMH testing may be required where there is diagnostic uncertainty. [7] [8] No single ovarian reserve test is sufficiently accurate on its own, so FSH is typically interpreted together with age and other hormonal and ultrasound parameters rather than in isolation. [6]
What levels mean
In primary ovarian insufficiency the diagnosis is confirmed by detection of raised FSH and declined oestradiol concentrations in the serum, indicating a primary ovarian defect. [9] A significant change from the previous 2015 guideline is that only one elevated FSH above 25 IU is required for the diagnosis of premature ovarian insufficiency. [7]
Community knowledge
## Tracking FSH Over Time
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- 1.Valera H, Chen A, Grive KJ. The Hypothalamic-Pituitary-Ovarian Axis, Ovarian Disorders, and Brain Aging. Endocrinology · 2025
- 2.Bosch E, Alviggi C, Lispi M, Conforti A, Hanyaloglu AC, Chuderland D, Simoni M, Raine-Fenning N. Reduced FSH and LH action: implications for medically assisted reproduction. Hum Reprod · 2021
- 3.Bousfield GR, Harvey DJ. Follicle-Stimulating Hormone Glycobiology. Endocrinology · 2019
- 4.de Kretser DM, Loveland KL, Meinhardt A, Simorangkir D, Wreford N. Spermatogenesis. Hum Reprod · 1998
- 5.Broekmans FJ, Soules MR, Fauser BC. Ovarian aging: mechanisms and clinical consequences. Endocr Rev · 2009
- 6.Coccia ME, Rizzello F. Ovarian reserve.
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