Anti-Müllerian hormone (AMH)
A hormone released by small ovarian follicles. Often high in PMOS, because there are more of those follicles than usual.
Anti-Müllerian hormone is produced by the small, developing follicles in the ovary. Because it reflects how many of those follicles are present, AMH is used as a rough marker of ovarian reserve.
In PMOS, AMH is often elevated. The ovaries carry a larger-than-usual number of small follicles that have stalled partway through maturation, and each one contributes AMH. A high level is a consequence of the same stalled-maturation pattern that produces the polycystic ovary morphology seen on ultrasound.
AMH is being studied as a possible stand-in for the ultrasound criterion in PMOS diagnosis, since it measures something related. It is not yet a formal diagnostic threshold in the current guideline, and levels vary by assay and by lab, so a single number is read in context rather than on its own.