Most people meet follicle-stimulating hormone (FSH) and luteinizing hormone (LH) for the first time in a fertility workup or a perimenopause panel, usually as a pair of unfamiliar acronyms attached to a number. But the story underneath them is simpler than the names suggest. FSH and LH are the two hormones your pituitary gland sends out to ask the ovaries or testes to do their job. What changes, over a cycle and over a lifetime, is not the question. It is how loudly the brain has to ask it, and how well the answer comes back.
What FSH and LH actually do
Both hormones are made and released by the pituitary gland, a small gland at the base of the brain, under instruction from the hypothalamus above it. In women who menstruate, FSH helps control the menstrual cycle: it triggers the growth of eggs in the ovaries and gets them ready for ovulation, when an ovary releases an egg to travel down a fallopian tube. LH works alongside it. Levels of LH rise quickly just before ovulation, and that monthly surge is what actually triggers the release of the egg.
In men, the division of labor looks different but runs on the same two hormones. FSH helps control the amount of sperm the testicles make and affects how healthy that sperm is, while LH causes the testicles to make testosterone, which is itself needed for sperm production. Cleveland Clinic describes the two hormones as gonadotropins, a pair that work together across a hormonal loop called the hypothalamic-pituitary-gonadal axis: the hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses, the pituitary answers with FSH and LH, and those two travel through the bloodstream to bind receptors on the ovaries or testes. The gonads then release their own hormones, estrogen, progesterone, or testosterone, which travel back up and tell the hypothalamus how much GnRH to release next. It is a closed loop, and each side of it is listening to the other. Cleveland Clinic notes that low-frequency pulses of GnRH favor more FSH production while high-frequency pulses favor more LH, and that in men a separate hormone called inhibin B, released by the testes, blocks FSH secretion as part of the same loop.
Why both climb as the ovaries answer less
The reason FSH and LH become a fixture of perimenopause conversations comes directly out of that feedback loop. As a woman's ovarian reserve declines through her late 30s and 40s, the remaining follicles become less responsive to the same FSH and LH signals that used to work reliably. The ovaries make less estrogen and less inhibin in return, which are exactly the hormones that normally tell the pituitary to ease off. With less negative feedback arriving, the pituitary does the only thing it knows how to do: it turns the signal up. FSH and LH both rise, not because the pituitary is malfunctioning, but because it is compensating for an audience that is answering less.
Cleveland Clinic's reference ranges make the scale of that rise concrete. In adult women past puberty, a normal FSH level runs roughly 4.7 to 21.5 mIU/mL. After menopause, that range jumps to roughly 25.8 to 134.8 mIU/mL, a shift of an order of magnitude. Testing.com's laboratory data shows a similar pattern using slightly different cut points: a follicular-phase range of about 2.5 to 10.2 mIU/mL climbing to roughly 23.0 to 116.3 mIU/mL after menopause. FSH generally makes this climb somewhat more dramatically than LH does, which is why clinicians and lab guides frequently describe FSH as the more diagnostic of the pair for ovarian failure, while LH is read alongside it for context rather than used on its own.
Why one reading rarely settles anything
The same feedback loop that makes FSH and LH rise in perimenopause is also what makes a single test result so hard to interpret during that transition. Because the ovaries are responding inconsistently rather than uniformly shutting down, hormone levels swing. Testing.com notes plainly that FSH fluctuates day to day, surges at ovulation, and can swing widely during perimenopause, and that a high reading in women of reproductive age is not enough on its own to confirm reduced ovarian reserve or primary ovarian insufficiency, since FSH can be high one month and normal the next. That is why providers typically want a second reading weeks apart before drawing a conclusion, and why MedlinePlus advises that testing usually is not needed at all for women 45 or older with typical symptoms, since a high FSH at that age is expected rather than diagnostic. The standard for confirming menopause itself remains behavioral, not hormonal: twelve consecutive months without a period.
This is also why FSH and LH are almost always ordered as a pair, and often alongside estradiol, testosterone, or progesterone. MedlinePlus describes an FSH test as one that is often used together with an LH test, since the two hormones work together to control sexual development and reproduction, and a provider reading either result will weigh it against the other, against symptoms, age, and medical history, not in isolation. The ratio between the two carries its own information. In polycystic ovary syndrome, for example, Testing.com notes that FSH often runs normal or low-normal while LH runs higher, sometimes producing an elevated LH-to-FSH ratio, although that pattern is not present in every case and is not by itself a diagnostic criterion.
Where FSH and LH testing does earn its place
None of this means the test is pointless outside of routine perimenopause screening. FSH and LH remain genuinely useful, and sometimes essential, in a narrower set of situations. MedlinePlus lists these as including difficulty conceiving after twelve months of trying, irregular or stopped periods at any age, and especially menopause-like symptoms appearing before age 45, where premature or early ovarian insufficiency needs to be distinguished from a pituitary or hypothalamic problem instead. In men, the same two hormones help evaluate low sperm count, low testosterone, low sex drive, or suspected testicular dysfunction.
The distinction that matters clinically is the direction of the abnormality. High FSH and LH generally point to a problem in the ovaries or testes themselves, since the pituitary is shouting because the gonads are not answering. Low FSH and LH generally point the other way, to a problem with the pituitary gland or hypothalamus itself failing to send the signal in the first place, a pattern that can also show up with rapid weight loss, being significantly underweight, or extreme exercise. Reading the number without that context tells you far less than reading it alongside the rest of the picture.
Common questions
Do FSH and LH levels alone diagnose menopause?
No. Testing.com notes that menopause is confirmed after twelve consecutive months without a period, and that providers look for consistently high FSH on two readings taken weeks apart as supporting evidence, not a standalone diagnosis. MedlinePlus similarly advises that FSH or LH testing usually is not needed for women 45 or older with typical symptoms, since a rise at that age and stage is expected rather than diagnostic on its own.
Why do FSH and LH get tested together instead of on their own?
Because they work as a linked pair inside the same feedback loop. MedlinePlus describes FSH testing as commonly paired with an LH test, since the two hormones work closely together to control sexual development and reproduction, and a provider interprets either result in light of the other, along with age, sex, symptoms, and history.
Can men have abnormal FSH and LH too?
Yes. In men, FSH supports sperm production and LH triggers testosterone production in the testes. High levels in men can point to primary testicular failure from causes such as injury, mumps, or a chromosomal condition, according to MedlinePlus, while low levels point toward a pituitary or hypothalamic problem instead.
Does a high FSH always mean low ovarian reserve?
Not reliably from one reading. Testing.com points out that FSH can look normal even when ovarian reserve is already declining, and that anti-Müllerian hormone (AMH) is a more sensitive marker for reserve because, unlike FSH, it does not fluctuate with the menstrual cycle.
What can throw off an FSH or LH result?
Cycle timing matters most, since both hormones rise and fall across the month. Testing.com also notes that hormonal contraceptives, hormone therapy, certain fertility medications, heavy alcohol use, extreme exercise, large weight changes, and high stress can all temporarily shift FSH levels, which is why providers ask about these before interpreting a result.
