FSH
Meaning of FSH: A pituitary hormone that tells the ovaries to ripen an egg and the testicles to keep making sperm.
Definition of FSH
FSH stands for follicle-stimulating hormone, a chemical messenger released by the pituitary gland at the base of the brain. In women it drives the growth of ovarian follicles, the fluid-filled sacs each containing an egg, and prompts them to make estrogen. In men it acts on the supporting cells of the testicles to sustain sperm production. Its level is measured to assess fertility and gland function.
How is its release controlled?
A region of the brain releases a signaling hormone in pulses, and the pituitary gland responds by secreting this hormone into the blood. The organs it acts on send signals back. Rising estrogen from a growing follicle, and a protein called inhibin from both ovary and testicle, damp down further release. The loop keeps output matched to what the organs are doing, and it explains the pattern of results seen in disease: when the ovary or testicle fails, the feedback disappears and the level climbs.
What do the results indicate?
| Pattern | What it suggests |
|---|---|
| High level, low sex hormones | The ovary or testicle is failing, as after menopause |
| Low level, low sex hormones | The problem lies in the pituitary or the brain above it |
| Raised in a young woman | Early loss of ovarian function |
| Raised in a man with low sperm count | Damage to the sperm-producing tissue itself |
Why does timing matter when it is measured?
The level swings through the menstrual cycle rather than sitting steady. It rises in the first days to recruit follicles, falls as estrogen from the leading follicle feeds back, and surges briefly around ovulation alongside the related luteinizing hormone. A sample taken without regard to cycle day can therefore be uninterpretable. For assessing ovarian reserve the convention is to test in the early days of the cycle. In men, who have no equivalent cycle, timing is not an issue.
How is it used in treatment?
Manufactured versions are central to fertility treatment. Given by injection, they push several follicles to develop at once rather than the single one a natural cycle produces, which is the basis of ovulation induction and of the collection step in assisted reproduction. Overstimulation is the recognized hazard, producing swollen ovaries and fluid shifts that can become serious, so response is tracked with ultrasound and blood tests throughout. In men, similar preparations are used alongside other hormones where sperm production has failed for pituitary reasons.
Also known as
Used in a sentence
Early cycle FSH was measured as part of the assessment of ovarian reserve.
Good to know
A high level with low sex hormones points to failure of the ovary or testicle itself, while a low level with the same picture points to the pituitary, and cycle day must be known for the result to be interpretable in women.