Perimenopause, menopause and the four stages

The one mechanism behind every state is the whole of it: the ovaries stop ovulating, so there is no corpus luteum, no progesterone, and therefore nothing to withdraw. Menstruation ends because ovulation ends. Everything else about the transition follows from ovulation becoming erratic on its way to stopping.

Menopause is a single day, and it can only be identified in hindsight: the day twelve consecutive months have passed since the final menstrual period. Everything people describe as "going through menopause" is actually perimenopause — the transition leading up to it, which commonly runs for years and produces the symptoms.

The transition is staged formally using STRAW+10, which anchors each stage to changes in cycle pattern rather than to symptoms or to a blood test. That matters, because it means your cycle history is the diagnostic instrument. A single FSH level in a woman still having periods tells you very little; FSH fluctuates widely across the transition, and a normal value does not exclude it.

Framework: Stages of Reproductive Aging Workshop +10 (STRAW+10), applied by the Perimenopause Stage Finder.