FSH is the pituitary's signal telling your ovaries to mature eggs; a high level means the signal has to shout because the ovaries are responding weakly.
That feedback logic is the whole interpretation. Healthy, well-stocked ovaries answer easily and FSH stays low. As egg supply drops or ovaries tire, the pituitary raises FSH to force a response, so high FSH points to diminished ovarian reserve or, with 12 months of missed periods, menopause. In children and teens, the same test sorts early from delayed puberty, and very low FSH in adults can flag pituitary or hypothalamus disorders. Two cautions for reading your own result: FSH swings across the cycle, so the draw is timed (typically day 3) and compared to that day's reference range, and it is interpreted together with AMH and estradiol, never solo. Over 45 with typical symptoms, testing is often skipped because high FSH is simply expected then. Ask for the combined read, not the single number.
What to do
Common questions
What is an FSH level?
FSH, follicle-stimulating hormone, is made by the pituitary gland at the base of your brain, and its job is to tell your ovaries to grow follicles and mature eggs. The blood test reads the volume of that signal. The logic is a feedback loop: when ovaries respond well, the pituitary whispers (lower FSH); when ovaries are running low on eggs or responding poorly, the pituitary shouts louder to get a response (higher FSH). That is why a high FSH on day 3 of the cycle suggests diminished ovarian reserve, and why persistently high FSH with irregular or stopped periods signals perimenopause or menopause. In people over 45 with classic symptoms, testing is usually unnecessary because high FSH is expected. FSH testing also runs the other direction: very low levels can point to a pituitary or hypothalamus problem, and in kids and teens the test helps explain early or delayed puberty. FSH is almost never read alone. It is interpreted alongside AMH (the egg-supply estimate), estradiol, and your cycle day, because FSH swings across the month and a single number without context misleads. If you get a result, ask what it means together with those companions, not in isolation.