what is follicle stimulating hormone?
follicle stimulating hormone, usually shortened to fsh, is produced by the pituitary gland, a small gland at the base of the brain. it is one of the key hormones that drives the menstrual cycle and plays an essential role in fertility for both women and men, though its effects differ between the sexes.
what does fsh do?
in women, fsh stimulates the growth of ovarian follicles, the small fluid filled sacs in the ovaries that each contain an egg. as a follicle matures under the influence of fsh, it produces increasing amounts of oestrogen. this rising oestrogen eventually feeds back to the brain and helps trigger the surge in luteinising hormone that leads to ovulation.
- stimulates follicle growth and development in the ovaries
- supports the production of oestrogen by developing follicles
- works as part of a feedback loop with the brain and ovaries
fsh across the menstrual cycle
fsh is typically higher at the very start of the menstrual cycle, helping to recruit and grow follicles for that cycle, then falls as oestrogen rises and one follicle becomes dominant. this rise and fall pattern repeats each cycle and is part of the finely tuned feedback system between the brain and the ovaries.
fsh and ovarian reserve
fsh levels tend to rise gradually with age, particularly as the number of eggs remaining in the ovaries declines. for this reason, fsh is sometimes used, alongside other measures, as part of an assessment of ovarian reserve or as an indicator of the approach of perimenopause and menopause, when fsh levels typically rise more markedly because the ovaries are producing less oestrogen.
what influences fsh levels?
fsh is influenced by age, stage of the menstrual cycle, and the overall function of the hypothalamus, pituitary gland and ovaries, sometimes referred to together as the hpo axis. certain medical conditions affecting this axis, some medications, and significant stress or changes in body weight can also affect fsh production.
why fsh testing needs context
because fsh naturally varies across the menstrual cycle and rises with age, a single fsh result needs to be interpreted alongside the day of the cycle it was taken, other hormone results, and an individual's broader health picture. it isn't a hormone that can be meaningfully assessed in isolation or interpreted through symptoms alone.
if you have questions about your fsh levels, fertility or menstrual cycle, please speak with a doctor or another qualified healthcare professional, who can advise on appropriate testing and what the results mean for you.