How is preeclampsia classified?

Classification of Preeclampsia

Preeclampsia is classified into two primary systems: by timing of onset (early-onset <34 weeks versus late-onset ≥34 weeks) and by severity (with or without severe features), with additional categories for preeclampsia superimposed on chronic hypertension and postpartum preeclampsia. 1

Classification by Timing of Onset

Early-onset preeclampsia (EOPE) develops before 34 weeks of gestation and arises from abnormal placentation with inadequate spiral artery remodeling and impaired uteroplacental perfusion, typically associated with more severe maternal and fetal outcomes including fetal growth restriction. 2, 3

Late-onset preeclampsia (LOPE) develops at or after 34 weeks of gestation and is mainly related to maternal cardiovascular and metabolic predisposition rather than primary placental dysfunction. 2

Term preeclampsia occurs at delivery ≥37 weeks of gestation, while preterm preeclampsia occurs at delivery <37 weeks of gestation. 3

Postpartum preeclampsia develops after delivery and represents a distinct classification, with eclamptic seizures potentially occurring for the first time in the early postpartum period. 1, 3

Classification by Severity

Preeclampsia Without Severe Features

• Blood pressure 140-159/90-109 mmHg (mild to moderate hypertension) 1
• Proteinuria ≥0.3 g/24 hours or protein:creatinine ratio ≥30 mg/mmol 1
• No evidence of end-organ dysfunction 1

Preeclampsia With Severe Features

Blood pressure criteria: Severe hypertension defined as BP ≥160/110 mmHg despite maintenance antihypertensive therapy. 1, 4

Maternal organ dysfunction includes any of the following:

• Renal: Serum creatinine >1.1 mg/dL or doubling of creatinine in absence of other renal disease; oliguria <500 mL/24 hours 1, 4
• Hepatic: Elevated liver transaminases (>2× upper limit of normal), persistent right upper quadrant or epigastric pain unresponsive to medication 1, 4
• Hematologic: Thrombocytopenia <100,000/μL, disseminated intravascular coagulation, hemolysis 1, 4
• Neurologic: New-onset severe persistent headache unresponsive to medication, visual disturbances (scotomata, cortical blindness), altered mental status, hyperreflexia with clonus, eclamptic seizures 1, 4
• Pulmonary: Pulmonary edema 1, 4
• Uteroplacental: Fetal growth restriction, abnormal umbilical artery Doppler, oligohydramnios 1

HELLP Syndrome

HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets) represents the severe end of the preeclampsia spectrum and is considered part of preeclampsia rather than a separate disorder, signifying more serious multisystem disease requiring urgent delivery consideration. 1, 4

Preeclampsia Superimposed on Chronic Hypertension

This classification applies when a woman with pre-existing chronic hypertension (BP ≥140/90 mmHg before pregnancy or before 20 weeks gestation) develops any new maternal organ dysfunction consistent with preeclampsia after 20 weeks. 1

• In the absence of preexisting proteinuria, new-onset proteinuria (≥0.3 g/24 hours) plus worsening BP after 20 weeks is sufficient for diagnosis 1
• In women with preexisting proteinuria, an increase in proteinuria alone is not sufficient; other maternal organ dysfunction must be present 1
• Approximately 25% of women with chronic hypertension develop superimposed preeclampsia, with higher rates in those with underlying renal disease 1

Gestational Hypertension

Gestational hypertension is pregnancy-induced hypertension (BP ≥140/90 mmHg) developing after 20 weeks without proteinuria or maternal organ dysfunction, complicating 6-7% of pregnancies. 1

• When proteinuria develops (≥0.3 g/24 hours), it is reclassified as preeclampsia 1
• Gestational hypertension is not uniformly benign; risk of complications depends on gestational age at onset 1

Antenatally Unclassifiable Hypertension

When BP is first recorded after 20 weeks gestation and hypertension is diagnosed, it cannot be classified antenatally as either chronic or gestational. Re-assessment is necessary at or after 42 days postpartum to determine if hypertension persists (indicating chronic hypertension) or resolves (indicating gestational hypertension). 1

Critical Diagnostic Considerations

Proteinuria is no longer required for diagnosis of preeclampsia if hypertension is accompanied by other evidence of maternal organ dysfunction, as proteinuria is present in only approximately 75% of cases. 1, 4

The diagnosis requires new-onset hypertension (BP ≥140/90 mmHg) at or after 20 weeks gestation plus either proteinuria or any maternal organ dysfunction listed above. 1, 4

Common Pitfalls to Avoid

• Do not assume preeclampsia requires all three classic findings (hypertension, edema, proteinuria); only hypertension plus one additional feature is needed 4, 5
• Pre-existing hypertension may be masked by the physiological BP fall in early pregnancy, leading to misclassification as gestational hypertension when BP rises later 1
• Rises in BP alone are insufficient to diagnose superimposed preeclampsia in women with chronic hypertension; new maternal organ dysfunction must be present 1
• Hyperreflexia is nonspecific and no longer included in diagnostic criteria, though new headache in the presence of hypertension should be considered preeclampsia until proven otherwise 1