Chronic Anovulation in PCOS
No ovulation means no corpus luteum ever forms.
- ~10%: PCOS prevalence (reproductive-age women)
- up to 100%: Anovulatory cycles (in PCOS patients)
- 0: Corpus luteum formed (without ovulation)
- primary: Progesterone source lost (luteal production absent)
Why ovulation stalls
High LH and insulin block follicle maturation.
No corpus luteum forms
Without a ruptured follicle, no progesterone source exists.
Cycle irregularity results
Periods become infrequent, unpredictable, or absent.
Unopposed Estrogen Exposure
Estrogen keeps building tissue with nothing to oppose it.
- ~0: Progesterone level (ng/mL without ovulation)
- ongoing: Estrogen source (follicular and peripheral)
- absent: Opposition mechanism (no luteal phase)
- growth-only: Endometrial signal (unbalanced stimulation)
Estrogen keeps signaling
Follicular and peripheral estrogen production continues unchecked.
Progesterone normally opposes it
Progesterone usually limits and matures the lining.
Peripheral aromatization adds fuel
Adipose tissue converts androgens into extra estrogen.
Endometrial Proliferation Without Shedding
The lining thickens progressively over unopposed months.
- ~28 days: Normal shedding cycle (typical menstrual cycle)
- months: Anovulation duration (lining keeps growing)
- rising: Endometrial thickness (no shedding trigger)
- increasing: Glandular crowding (proliferative overgrowth)
Growth without a stop signal
No progesterone withdrawal means no shedding trigger.
Glands crowd together
Proliferative glands multiply and pack more densely.
Thickness accumulates monthly
Each unopposed month adds more tissue depth.
Hyperplasia and Cancer Risk
Prolonged unopposed estrogen raises hyperplasia risk sharply.
- low: Simple hyperplasia risk (early unopposed exposure)
- rises: Atypical hyperplasia risk (with duration untreated)
- up to 29%: Cancer progression risk (untreated atypical hyperplasia)
- duration: Key driver (months of unopposed estrogen)
Simple to complex hyperplasia
Glandular crowding progresses toward structural complexity.
Atypia raises stakes
Cellular atypia signals a precancerous change.
Time is the driver
Longer unopposed exposure means higher cumulative risk.
Progestin Therapy Protects the Endometrium
Progestin restores balance and triggers protective shedding.
- 10–14 days: Cyclic progestin (monthly withdrawal bleed)
- daily: Continuous progestin (IUD or pill option)
- high: Hyperplasia regression (with adequate therapy)
- substantial: Risk reduction (restored opposition)
Progestin opposes estrogen
It counters growth signaling and matures the lining.
Shedding is restored
Withdrawal bleeding clears accumulated tissue safely.
Long-term protection
Regular progestin use lowers hyperplasia risk durably.