Pre-eclampsia & Eclampsia for USMLE Step 3
Start your One-Week Free Trial
Already subscribed? Log in »
Pre-eclampsia & Eclampsia for the USMLE Step 3 Exam
Overview of Pre-eclampsia and Eclampsia
- Definitions:
- Pre-eclampsia: New-onset hypertension (≥140/90 mmHg) after 20 weeks’ gestation with proteinuria (≥300 mg/24-hour urine collection or protein/creatinine ratio ≥0.3) or other signs of organ dysfunction.
- Eclampsia: New-onset tonic-clonic seizures in a patient with pre-eclampsia, not explained by other neurological disorders.
- Classification of Pre-eclampsia:
- Mild: Hypertension with proteinuria but without severe symptoms or laboratory abnormalities.
- Severe: Blood pressure ≥160/110 mmHg or evidence of end-organ damage, such as severe headache, visual disturbances, elevated liver enzymes, thrombocytopenia, or pulmonary edema.
Pathophysiology
- Placental Abnormalities and Endothelial Dysfunction:
- Poor placental development with shallow invasion of trophoblasts leads to inadequate remodeling of spiral arteries.
- Placental ischemia results in the release of antiangiogenic factors (e.g., sFlt-1) that block VEGF, causing systemic endothelial dysfunction.
- Endothelial injury contributes to vasoconstriction, vascular permeability, and a pro-coagulant state.
- Systemic Inflammation:
- Abnormal immune response triggers inflammation, which further damages endothelial cells and exacerbates hypertension and proteinuria.
Clinical Presentation
- Symptoms of Pre-eclampsia:
- Mild Pre-eclampsia: Typically asymptomatic or mild edema and headache.
- Severe Pre-eclampsia: Severe headache, vision changes (blurred vision or scotomata), right upper quadrant or epigastric pain, dyspnea due to pulmonary edema.
- Eclampsia:
- Manifests with generalized tonic-clonic seizures in the presence of pre-eclampsia symptoms.
- Often preceded by prodromal symptoms, such as severe headache or visual changes.
- Differential Diagnosis:
- Exclude other causes of seizures, including epilepsy, cerebrovascular accident, and metabolic derangements.
Diagnostic Evaluation
- Laboratory Tests:
- Urinary Protein: ≥300 mg in a 24-hour collection or protein-to-creatinine ratio ≥0.3.
- CBC: Thrombocytopenia (platelet count <100,000/mcL) is an indicator of severe disease.
- Liver Function Tests: Elevated AST/ALT suggests liver involvement; elevated bilirubin may indicate hemolysis.
- Renal Function: Elevated creatinine (>1.1 mg/dL) suggests renal impairment.
- Uric Acid: Elevated uric acid levels may correlate with disease severity.
- Imaging:
- Ultrasound: For fetal growth restriction and amniotic fluid volume assessment.
- Doppler Studies: Abnormal uterine artery Doppler flow indicates placental insufficiency.
Management and Treatment
- Antihypertensive Therapy:
- Target BP: Reduce blood pressure to <160/110 mmHg to prevent complications.
- Medications: First-line agents include labetalol, nifedipine, and hydralazine, all of which are safe in pregnancy.
- Seizure Prophylaxis and Management:
- Magnesium Sulfate: Gold standard for seizure prophylaxis in severe pre-eclampsia and treatment of eclampsia.
- Dosing: 4–6 g IV loading dose, followed by 1–2 g/hr infusion.
- Toxicity Monitoring: Reflexes, respiratory rate, and serum magnesium levels to prevent toxicity.
- Timing of Delivery:
- Severe Pre-eclampsia: Delivery recommended at ≥34 weeks or earlier if maternal or fetal status worsens.
- Steroids: Administered between 24–34 weeks to enhance fetal lung maturity in anticipation of preterm delivery.
Complications
- Maternal:
- HELLP Syndrome: Hemolysis, elevated liver enzymes, low platelet count; increased risk of hepatic rupture and renal failure.
- Cerebral Complications: Stroke or cerebral edema due to hypertensive crises.
- Pulmonary Edema: Secondary to endothelial dysfunction and fluid overload.
- Fetal:
- Intrauterine Growth Restriction (IUGR): Caused by impaired placental perfusion.
- Preterm Delivery: Often necessary due to maternal or fetal indications.
- Fetal Demise: Increased risk in cases of severe pre-eclampsia or poorly controlled hypertension.
Key Points
- Pre-eclampsia is defined by new-onset hypertension and proteinuria or organ dysfunction after 20 weeks; eclampsia involves seizures in the context of pre-eclampsia.
- Pathophysiology involves abnormal placental development, endothelial injury, and systemic inflammation.
- Severe pre-eclampsia presents with BP ≥160/110 mmHg or symptoms like headache, visual changes, or elevated liver enzymes.
- Magnesium sulfate is the primary agent for seizure prevention and treatment in pre-eclampsia/eclampsia.
- Delivery is the definitive treatment, particularly at ≥34 weeks or with worsening maternal/fetal status.
- Key maternal complications include HELLP syndrome and pulmonary edema; fetal risks include IUGR and preterm delivery.