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.
The placenta covers the cervix (the exit door for the baby), so when the cervix stretches or opens, the placenta tears and bleeds.
Pancake on the Wrong Shelf
Imagine a sticky pancake (the placenta) that should be mounted high on a kitchen cabinet shelf (the upper uterus), but it gets stuck to a lower shelf instead—right at the level of the cabinet's rolling door (the cervix). The pancake has veins of syrup running through it (maternal blood vessels in the placenta). When you open the rolling door, it slides upward and outward, stretching and thinning the shelf as it goes. Because the pancake is pinned in place and cannot stretch with the door, the syrup veins tear open as the door moves, leaking sticky syrup (maternal blood) all over the floor (vagina). The harder the door opens (cervix dilates), the worse the tear, until finally the flood is unstoppable.
ACOG Practice Bulletin No. 204: Fetal Macrosomia, 2019 (includes management of placenta previa) · Royal College of Obstetricians and Gynaecologists (RCOG) Green-top Guideline No. 27: Placenta Praevia and Placenta Accreta, 2018 · UpToDate Clinical Guidelines (Placenta Previa) · Society for Maternal-Fetal Medicine (SMFM) Consult Series · reviewed 2026-07-07