FSH (Follicle-Stimulating Hormone)

What FSH Measures

FSH is a gonadotropin, a hormone that acts on the gonads, and it's released by the anterior pituitary gland at the base of the brain.^[1] During the follicular phase of the cycle, FSH stimulates a group of ovarian follicles to mature, which is why it's grouped with LH as one of the two pituitary signals that drive the whole cycle.^[1] The pituitary doesn't release FSH at a flat, constant level. It moves in a curve shaped by what the ovaries are doing, and that back-and-forth between pituitary and ovary is the basic loop that runs the cycle.

Two hormones from the ovary hold FSH in check through negative feedback. Estrogen output from a growing follicle suppresses further FSH release, and so does inhibin, a hormone made by the same follicle cells.^[1] As the corpus luteum from the previous cycle breaks down at the end of the luteal phase, both estradiol and inhibin A fall off, and that drop is what lets FSH rise again to start the next cycle.^[2]

How It's Measured

FSH is most often measured from a blood draw, run as a standard immunoassay and usually reported alongside other hormones in a broader panel rather than as a standalone test. Because FSH is a cyclical hormone whose blood level depends heavily on which cycle day it's drawn, testing conventions call for an early-follicular draw, typically cycle day 2 through 4, so results can be compared on a consistent basis.^[4] That's a lab convention for standardizing results, not guidance about when any individual should get tested.

FSH can also be measured from urine. Research has used a urinary FSH subunit assay to track ovarian function over time, and urine-based FSH measurement shows up on some consumer ovulation and hormone-tracking panels alongside LH.^[5]

Why People Track FSH

FSH shows up most often as one line in a broader hormone panel, alongside LH, estradiol, and sometimes AMH, when someone is looking at fertility, cycle irregularity, or a hormone workup more generally. Because its concentration is part of the same feedback loop that produces the LH surge and ovulation, FSH is part of how researchers describe the mechanics of the menstrual cycle itself, not just a single stand-alone marker.^[2] Its role in the follicular phase is covered in more depth in our follicular phase entry, and the surge that ends that phase is covered in our LH surge entry.

AMH has largely replaced basal FSH testing as the standard ovarian-reserve marker in clinical practice, in part because AMH stays relatively stable across the cycle while FSH doesn't.^[4] See our AMH entry for how that marker compares. FSH is still tracked, though, both as part of routine hormone panels and as a population-level marker researchers use to describe the menopause transition, covered below.

How Go Go Gaia Tracks FSH

FSH is a lab value, not something a wearable or a daily log can capture. Upload a lab report PDF or CSV to the web app and Go Go Gaia pulls the FSH value out, stores it, and charts it on your timeline alongside your cycle day and other logged metrics. You see it in context with the rest of what you track over time, instead of as a number sitting alone in a PDF.

What the Research Shows

The FSH curve across a single cycle is well characterized: it rises as the corpus luteum from the prior cycle breaks down and estradiol and inhibin A fall, then a second, smaller FSH rise occurs around the time of the LH surge at ovulation, driven partly by the same progesterone increase that accompanies that surge.^[2]

Across the menopause transition, population data from the Study of Women's Health Across the Nation followed more than 3,200 midlife women and found that FSH concentrations increased significantly with age, with a steeper rise at older ages within the transition.^[3] That's a population-level pattern describing how FSH trends across large groups of women over years, not a way to determine any individual's menopause status from a single reading.

Related Terms

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

What does FSH stand for?

FSH stands for follicle-stimulating hormone. It's made and released by the pituitary gland at the base of the brain, and it acts on the ovaries to recruit follicles for growth each cycle.

Why is blood FSH testing usually done early in the cycle?

FSH is a cyclical hormone that rises and falls with the rest of the menstrual cycle, so its concentration in blood depends heavily on which cycle day it's drawn. Testing conventions call for an early-follicular draw, typically cycle day 2 through 4, so results can be compared on a consistent basis. That's a lab convention, not personal guidance about when any individual should get tested.

Does FSH only show up in blood tests?

No. FSH can also be measured from urine. A urinary FSH subunit assay has been used in research to track ovarian function, and urine-based FSH measurement appears on some consumer ovulation and hormone-tracking panels alongside LH.