Can aspirin (acetylsalicylic acid) help lower the risk of pre-eclampsia?

Low-Dose Aspirin for Prevention of Preeclampsia

Yes, low-dose aspirin significantly reduces the risk of preeclampsia in high-risk pregnant women, with studies showing a 24% reduction in preeclampsia risk and additional reductions in preterm birth and intrauterine growth restriction. 1

Patient Selection for Aspirin Therapy

Low-dose aspirin should be initiated for women with:

High-Risk Factors (any one of these):

• Previous history of preeclampsia
• Multifetal gestation (twins, triplets)
• Chronic hypertension
• Type 1 or 2 diabetes
• Renal disease
• Autoimmune diseases (especially systemic lupus erythematosus)
• Antiphospholipid syndrome 2, 1

Moderate-Risk Factors (consider aspirin if multiple factors present):

• Nulliparity (first pregnancy)
• Maternal age ≥35 years
• BMI >30 kg/m²
• Family history of preeclampsia (mother or sister)
• Sociodemographic risk factors
• Conception through assisted reproductive technology 1

Dosage and Timing

The optimal approach for aspirin prophylaxis:

• Dosage:

  • 81-150 mg daily, with evidence suggesting higher doses may be more effective
  • ACOG and USPSTF recommend 81 mg daily (standard US dosage)
  • European guidelines and RCOG recommend 150 mg daily 1, 3
  • Recent evidence suggests 162 mg may be more effective than 81 mg (14.2% vs 10.1% preeclampsia rate) without increased bleeding complications 4

• Timing:

  • Start between 12-16 weeks of gestation (optimal timing)
  • Continue until delivery
  • Efficacy is significantly greater when initiated before 16 weeks 2, 1, 5
  • Starting after 16 weeks shows smaller or no reduction in preeclampsia risk 5

• Administration:

  • Taking aspirin at bedtime may maximize effectiveness 1, 6

Mechanism and Efficacy

Low-dose aspirin works through:

• Inhibition of thromboxane A2 (vasoconstrictor and platelet aggregator)
• Promotion of prostacyclin (vasodilator)
• Improving placental perfusion during critical placentation 1, 2

The efficacy of aspirin prophylaxis includes:

• 24% reduction in preeclampsia risk in high-risk women
• 14% reduction in preterm birth risk
• 20% reduction in intrauterine growth restriction risk
• 62% reduction in preterm preeclampsia when 150 mg is used before 16 weeks 1, 6
• 68% reduction in neonatal intensive care unit stays 6

Safety Profile

Low-dose aspirin in pregnancy has demonstrated:

• No increased risk of placental abruption
• No increased risk of postpartum hemorrhage
• No increased risk of fetal intracranial bleeding or congenital anomalies
• No increased risk of maternal or fetal adverse outcomes 2, 4

Even at higher doses (162 mg), studies have not shown increased rates of postpartum hemorrhage, postpartum hematoma, or intraventricular hemorrhage in newborns 4

Special Considerations

• Chronic Hypertension: Some evidence suggests aspirin may be less effective in women with pre-existing chronic hypertension 6

• Systemic Lupus Erythematosus: All pregnant women with SLE should receive low-dose aspirin (81-100 mg daily) 1

• Antiphospholipid Syndrome: Low-dose aspirin should be combined with prophylactic-dose heparin/LMWH 1

Common Pitfalls to Avoid

1. Starting too late: Initiating aspirin after 16 weeks significantly reduces its effectiveness 1, 5

2. Using inadequate dosing: Evidence suggests doses <100 mg may be less effective than higher doses 3, 5

3. Discontinuing too early: Aspirin should be continued until delivery 2, 1

4. Missing high-risk patients: Failing to identify all women who would benefit from aspirin prophylaxis 1

5. Poor adherence: Patient education about consistent daily use is crucial for effectiveness 1

Low-dose aspirin represents one of the few effective interventions for preventing preeclampsia and its associated complications, particularly when properly administered to appropriate high-risk women.