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.
Blood pressure was already high before pregnancy or climbed before twenty weeks — the blood vessels were damaged before the baby even arrived.
Old, Clogged Pipes in a Growing House
Imagine a house's plumbing system before a big renovation: the pipes are already thick-walled, narrow, and crusty from years of high water pressure. Now the owners add fifty percent more water flow (pregnancy blood volume) because they're building a new wing (the baby and placenta). The old pipes cannot stretch open the way new pipes would — the pressure stays dangerously high because the water has nowhere to go. Meanwhile, the main water line to the new wing (spiral arteries feeding the placenta) never widens from a pinhole to a garden hose the way it should; it stays pinched. So the new wing gets starved for water (the baby gets less oxygen and nutrients), and the stress on the old plumbing system (kidneys, liver, brain) gets worse with each day. Finally, if a leak springs (preeclampsia) or a pipe bursts (abruption), the whole system fails and the renovation must stop immediately (early delivery).
ACOG Practice Bulletin No. 203: Chronic Hypertension in Pregnancy (2019, reaffirmed 2021) · American Heart Association / American College of Cardiology Hypertension Guideline (2017) · UpToDate: Preexisting Hypertension in Pregnancy · CDC: High Blood Pressure During Pregnancy · reviewed 2026-07-07