Phase 1 · Understand the Body — Why the disease behaves the way it does.
The One-Line Truth
The whole disease in one chain
Everything on this page exists to explain this line.
Abnormal uterine bleeding (periods that are too heavy, too long, too often, or happen at the wrong time) happens when something breaks the normal hormone cycle, a growth forms in the uterus, blood clotting fails, or cancer develops.
The Lining's Leaky Roof Repair Crew
Imagine your uterus is a house, and the endometrium (lining) is the roof. In a normal cycle, estrogen is the construction crew that builds the roof thicker and stronger for 14 days, then progesterone arrives as the supervisor who says "stop building, seal everything up, and prepare for tenants." When progesterone leaves (period time), the roof is supposed to shed in an orderly way—workers unscrew shingles calmly, and a repair team (platelets and fibrin, like caulk and mesh) seals the nail holes before water leaks. But when anovulation happens, the construction crew never stops—the roof keeps getting thicker and thicker with no supervisor to organize the teardown, so when it finally collapses, shingles fly everywhere and nail holes stay open, flooding the house (heavy bleeding). When a structural problem exists (a polyp is like a rotten beam, a fibroid like a weight crushing one corner), the roof is already broken before teardown even starts, so water pours out during the normal "tear down" phase. When impaired blood clotting (coagulopathy) happens (clotting disorder), the repair team (platelets and fibrin) never shows up, so even a normal roof shedding leaves gaping holes that bleed for days.
ACOG Practice Bulletin No. 128: Diagnosis of Abnormal Uterine Bleeding in Reproductive-Aged Women (reaffirmed 2023) · FIGO Menstrual Disorders Committee: PALM-COEIN Classification System (2018) · American College of Physicians: Evaluation and Management of Abnormal Uterine Bleeding (2021) · CDC Heavy Menstrual Bleeding Guidelines (2023) · reviewed 2026-07-07