Clinical meaning
Preeclampsia is a multisystem hypertensive disorder of pregnancy characterized by new-onset hypertension (systolic greater than or equal to 140 mmHg or diastolic greater than or equal to 90 mmHg on two occasions at least 4 hours apart) developing after 20 weeks gestation with proteinuria (greater than or equal to 300 mg/24 hours or protein/creatinine ratio greater than or equal to 0.3) or evidence of end-organ dysfunction. The pathophysiology originates from defective trophoblast invasion of the spiral arteries during placentation (weeks 8-18): normally, extravillous cytotrophoblasts remodel spiral arteries into low-resistance, high-capacity vessels by replacing the muscular and endothelial layers. In preeclampsia, this remodeling fails, leaving spiral arteries with intact muscular walls that maintain high resistance, reducing uteroplacental perfusion and creating a hypoxic placental environment.
The ischemic placenta releases anti-angiogenic factors into the maternal circulation -- soluble fms-like tyrosine kinase 1 (sFlt-1) binds and neutralizes vascular endothelial growth factor (VEGF) and placental growth factor (PlGF), while soluble endoglin (sEng) impairs TGF-beta signaling in endothelial cells. The resulting systemic endothelial dysfunction causes widespread vasospasm (hypertension), increased vascular permeability (edema, proteinuria), platelet activation and consumption (thrombocytopenia), hepatocellular damage (elevated liver enzymes, right upper quadrant pain), cerebral edema (headache, visual disturbances, seizures in eclampsia), and uteroplacental insufficiency (fetal growth restriction, oligohydramnios, abnormal Doppler velocimetry).
Severe features include systolic blood pressure greater than or equal to 160 mmHg or diastolic greater than or equal to 110 mmHg, thrombocytopenia (platelet count less than 100,000/microL), liver transaminases elevated to twice the upper limit of normal, persistent right upper quadrant or epigastric pain, serum creatinine greater than 1.1 mg/dL or doubling of baseline, pulmonary edema, or new-onset cerebral or visual disturbances. HELLP syndrome (Hemolysis with elevated LDH and schistocytes on smear, Elevated Liver enzymes, Low Platelets) represents a severe variant with microangiopathic hemolytic anemia and carries significant maternal morbidity.