Detailed definition
Inhibin B is a heterodimeric glycoprotein hormone of the TGF-β family, produced by granulosa cells of small antral follicles. It suppresses pituitary FSH secretion through negative feedback, working alongside estradiol to keep FSH within a narrow range during the reproductive years. As the cohort of small follicles declines with ovarian aging, inhibin B falls, the pituitary loses its inhibitory signal, and FSH rises — this is the earliest measurable hormonal change in the menopause transition, often preceding noticeable estradiol decline. Inhibin B measurement is used primarily in research settings and in evaluating ovarian reserve in fertility medicine. It is not routinely ordered in a typical menopause workup.
Why it matters in menopause
Inhibin B helps explain why FSH rises before estradiol falls noticeably — it is the loss of inhibin B feedback, more than estradiol decline, that drives early FSH elevation. This is why women in late reproductive age can have rising FSH while still having reasonably normal estradiol levels, and why FSH is unreliable for diagnosing the exact stage of perimenopause.
Related terms
Sources
External references: Wikipedia.