It starts at the placenta
Preeclampsia is thought to begin early in pregnancy with abnormal placentation. Normally, fetal trophoblast cells remodel the maternal spiral arteries into wide, low-resistance vessels that deliver ample blood. When this remodeling is incomplete, the placenta receives less blood and becomes intermittently ischemic as pregnancy advances and demand grows.
This places the root cause in the first half of pregnancy, often well before symptoms appear, even though the condition is usually detected later through high blood pressure and protein in the urine.
From placental stress to whole-body disease
The stressed placenta releases anti-angiogenic factors, notably soluble fms-like tyrosine kinase-1 (sFlt-1), which mops up circulating VEGF and placental growth factor. With these vessel-supporting signals depleted, the mother's vascular endothelium becomes dysfunctional throughout the body, producing high blood pressure, leaky vessels, kidney involvement, and risk to the liver and brain.
Severity ranges from mild to life-threatening, and delivery of the placenta is the definitive resolution. This is general educational information, not medical advice; blood-pressure changes or warning symptoms in pregnancy need prompt assessment by a qualified clinician.