Preeclampsia Prevention and Management: Aspirin Prophylaxis Evidence
Preeclampsia Epidemiology and Risk Stratification
Preeclampsia affects 3-8% of pregnancies and remains a leading cause of maternal and perinatal morbidity and mortality worldwide. The USPSTF and ACOG recommend aspirin prophylaxis for women with high-risk factors: prior preeclampsia, multifetal gestation, chronic hypertension, pregestational diabetes, renal disease, or autoimmune disease. Women with multiple moderate-risk factors (nulliparity, obesity with BMI above 30, family history of preeclampsia, age 35 or older, prior adverse pregnancy outcome) should also be considered for aspirin. The ACOG recommendation is to start low-dose aspirin at 12-16 weeks gestation in eligible patients.
ASPRE Trial: The Landmark Prevention Evidence
The ASPRE (Aspirin for Evidence-Based Preeclampsia Prevention) trial randomized 1,776 women identified as high-risk by first-trimester combined screening to aspirin 150 mg nightly versus placebo. Aspirin reduced preterm preeclampsia (delivery before 37 weeks) by 62% (OR 0.38, 95% CI 0.20-0.74, p = 0.004). The reduction for term preeclampsia was not significant (OR 0.95). This trial demonstrated that the benefit is concentrated in preterm preeclampsia prevention and that first-trimester screening using a combination of maternal risk factors, uterine artery Doppler, mean arterial pressure, and serum biomarkers (PAPP-A, PlGF) identifies the highest-risk population for intervention.
Aspirin Dosing: 81 mg vs 150 mg and Timing
North American practice predominantly uses aspirin 81 mg daily, while European centers use 150 mg based on the ASPRE protocol. A network meta-analysis of 45 trials (20,909 women) demonstrated a dose-response effect: aspirin 100-150 mg daily reduced preeclampsia risk by 33-62%, while doses below 100 mg showed a more modest 10-24% reduction. Bedtime dosing is recommended based on evidence that nighttime administration provides superior blood pressure reduction through effects on circadian prostacyclin/thromboxane balance. Aspirin should be initiated between 12-16 weeks (optimally before 16 weeks) and continued until 36 weeks gestation or delivery.
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Magnesium Sulfate for Seizure Prophylaxis
Magnesium sulfate is the gold standard for eclampsia prophylaxis in severe preeclampsia. The Magpie trial (10,141 women) demonstrated a 58% reduction in eclampsia risk (RR 0.42, 95% CI 0.29-0.60). Standard protocol: 4-6 g IV loading dose over 20-30 minutes followed by 1-2 g/hour continuous infusion for 24-48 hours after delivery or last seizure. Monitor patellar reflexes, urine output (target above 30 mL/hour), and respiratory rate. Therapeutic range is 4.8-8.4 mg/dL; toxicity manifests as loss of deep tendon reflexes (above 10 mg/dL) and respiratory depression (above 12 mg/dL). Calcium gluconate 1g IV is the antidote for magnesium toxicity.
Delivery Timing and Postpartum Surveillance
Delivery is the definitive treatment for preeclampsia. Current recommendations: deliver at 37 weeks for preeclampsia without severe features, and at 34 weeks (or earlier if maternal or fetal status deteriorates) for preeclampsia with severe features. Postpartum preeclampsia can develop up to 6 weeks after delivery, and patients should be counseled on warning signs (severe headache, visual changes, epigastric pain, new hypertension). Women with a history of preeclampsia have a 2-4 fold increased lifetime cardiovascular disease risk and should receive long-term cardiovascular risk assessment and modification.
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