Preeclampsia: The Placenta-Driven Vascular Crisis of Pregnancy

What it is and why it matters clinically

Preeclampsia complicates roughly 2–8% of pregnancies and, together with eclampsia and HELLP syndrome, ranks among the leading causes of maternal and perinatal morbidity and mortality worldwide. It is a pregnancy-specific syndrome — it does not occur outside of pregnancy (or the immediate postpartum period) because its trigger is the placenta itself.

• Maternal risk: stroke, eclamptic seizures, pulmonary edema, acute kidney injury, hepatic rupture, DIC, and placental abruption.
• Fetal risk: iatrogenic prematurity, fetal growth restriction, oligohydramnios, and stillbirth from placental insufficiency.
• Long-term: a history of preeclampsia roughly doubles lifetime cardiovascular and chronic kidney disease risk.

Because it is silent until advanced, screening rests on serial blood-pressure and urine checks at every prenatal visit. Key risk factors include nulliparity, prior preeclampsia, chronic hypertension, pregestational diabetes, chronic kidney disease, obesity, multifetal gestation, antiphospholipid syndrome, and extremes of maternal age.

The mechanism, step by step

Preeclampsia is a two-stage disease. Stage 1 (placental, weeks 8–18): extravillous cytotrophoblasts fail to adequately invade and remodel the maternal spiral arteries. Normally these vessels are converted into wide, low-resistance conduits; in preeclampsia they stay narrow and high-resistance, producing chronic placental ischemia and oxidative stress.

Stage 2 (maternal, clinical): the stressed placenta releases anti-angiogenic factors into the maternal circulation — chiefly soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin (sEng).

• sFlt-1 is a decoy receptor that binds and sequesters circulating VEGF and placental growth factor (PlGF), starving the endothelium of pro-survival signals.
• sEng antagonizes TGF-β/nitric-oxide signaling, impairing vasodilation.

The net effect is diffuse maternal endothelial dysfunction: loss of NO and prostacyclin, rise in thromboxane and endothelin-1, vasoconstriction, increased vascular permeability (edema, proteinuria), and a procoagulant, platelet-consuming state. Glomerular endotheliosis is the classic renal lesion.

Clinical presentation and classic signs

The hallmark is new-onset hypertension after 20 weeks, often accompanied by edema (now a nonspecific finding, dropped from formal criteria). Many women are asymptomatic — the danger of the disease. When symptoms appear, they signal severe disease and warn of impending eclampsia:

• Neurologic: persistent frontal/occipital headache, visual disturbances (scotomata, blurring, photopsia), hyperreflexia and clonus.
• Hepatic: right-upper-quadrant or epigastric pain from hepatic capsular stretch (Glisson's capsule) — a red flag for HELLP.
• Pulmonary: dyspnea from pulmonary edema.
• Rapid weight gain and nondependent (facial/hand) edema.

The feared endpoint is eclampsia — generalized tonic-clonic seizures — which can occur antepartum, intrapartum, or up to ~4 weeks postpartum, sometimes without preceding severe hypertension. In HELLP syndrome, the presentation may be dominated by malaise, nausea, and RUQ pain with only mildly elevated pressures, making it easy to miss.

Diagnosis: the specific criteria and cutoffs

Per ACOG, preeclampsia requires new-onset hypertension — systolic ≥140 or diastolic ≥90 mmHg on two readings at least 4 hours apart after 20 weeks — plus one of:

• Proteinuria: ≥300 mg/24 h, urine protein/creatinine ratio ≥0.3 mg/mg, or dipstick 2+ (if quantitative testing unavailable).
• Or, without proteinuria, any severe feature: platelets <100,000/µL; serum creatinine >1.1 mg/dL (or doubling); AST/ALT ≥2× upper normal; pulmonary edema; or new cerebral/visual symptoms.

Severe-range hypertension is ≥160 systolic or ≥110 diastolic. In HELLP, look for hemolysis (LDH ≥600 U/L, schistocytes, low haptoglobin, indirect bilirubin ≥1.2), elevated liver enzymes, and low platelets (Tennessee/Mississippi classifications).

The sFlt-1/PlGF ratio is now a validated tool: a ratio ≤38 has high negative predictive value to rule out preeclampsia within one week. Uterine artery Doppler showing high resistance supports the diagnosis of placental insufficiency.

Management at a mechanism level and complications

Delivery is the only cure — it removes the placental source of anti-angiogenic factors. Timing balances maternal risk against fetal prematurity: deliver at ≥37 weeks for preeclampsia without severe features, and at ≥34 weeks (or immediately if unstable) for severe features. Until then, three drug goals:

• Seizure prophylaxis — magnesium sulfate: the drug of choice for preventing/treating eclampsia. It acts as an NMDA-receptor antagonist and cerebral vasodilator, raising the seizure threshold. Watch for toxicity — loss of deep tendon reflexes, then respiratory depression; the antidote is IV calcium gluconate.
• Acute BP control: IV labetalol, IV hydralazine, or oral nifedipine for severe-range pressures, to prevent maternal stroke (the leading cause of death). ACE inhibitors/ARBs are contraindicated (fetal renal toxicity).
• Antenatal corticosteroids (betamethasone) if <34 weeks to accelerate fetal lung maturity.

Low-dose aspirin (81–162 mg) started at 12–16 weeks reduces incidence in high-risk women by inhibiting thromboxane-driven vasoconstriction.

Distinctions from mimics and key pitfalls

Not all pregnancy hypertension is preeclampsia. Chronic hypertension predates 20 weeks; gestational hypertension lacks proteinuria and severe features (though ~25% progress). Superimposed preeclampsia arises when a chronically hypertensive patient develops new end-organ dysfunction.

• Don't-miss #1 — HELLP without hypertension: up to 15% of HELLP cases have normal or minimally elevated BP; RUQ pain plus low platelets should trigger a smear, LDH, and transaminases.
• Don't-miss #2 — postpartum preeclampsia/eclampsia: a new headache or seizure days after delivery is preeclampsia until proven otherwise; delivery does not confer immediate immunity.
• Mimics to exclude: TTP/HUS (ADAMTS13, more severe hemolysis/renal failure, fever, neuro), acute fatty liver of pregnancy (hypoglycemia, coagulopathy, ammonia), and lupus flare or thrombotic microangiopathy.

Finally, remember that edema and mild BP elevation understate the danger — the disease can decompensate rapidly, and the absence of proteinuria does not exclude it once severe features are present.

Hypertensive disorders of pregnancy and how to tell them apart

Disorder	Onset / BP	Proteinuria or end-organ signs	Key distinguishing feature
Chronic hypertension	Before 20 wk (or persists >12 wk postpartum)	May be absent	Predates pregnancy; not placenta-driven
Gestational hypertension	≥140/90 after 20 wk	None	No proteinuria and no severe features (may progress to preeclampsia)
Preeclampsia	≥140/90 after 20 wk	Proteinuria OR renal/hepatic/hematologic/CNS/pulmonary dysfunction	Hypertension PLUS end-organ involvement
Preeclampsia with severe features	≥160/110, or severe symptoms	Plt <100k, Cr >1.1, AST/ALT 2× normal, pulmonary edema, cerebral/visual symptoms	Any one severe feature mandates delivery timing decisions
HELLP syndrome	Often ≥20 wk, can be postpartum	Hemolysis, LDH ↑, AST/ALT ↑, Plt <100k	Hemolysis + liver + thrombocytopenia; BP may be near-normal
Eclampsia	Any, incl. postpartum	Preeclampsia features + seizure	New-onset tonic-clonic seizure not otherwise explained