Aspirin Regimen for Preeclampsia Prevention in High-Risk Pregnant Women
Low-dose aspirin (81 mg/day) should be initiated between 12-16 weeks of gestation and continued daily until delivery for pregnant women at high risk of preeclampsia. 1
Patient Selection Criteria
High-Risk Factors (≥1 indicates aspirin therapy)
- History of preeclampsia
- Multifetal gestation
- Chronic hypertension
- Type 1 or type 2 diabetes
- Renal disease
- Autoimmune diseases (especially SLE and APS)
Moderate-Risk Factors (≥2 indicate aspirin therapy)
- First pregnancy
- Maternal age ≥35 years
- BMI >30 kg/m²
- Family history of preeclampsia
- Sociodemographic risk factors 1, 2
Recommended Dosing and Timing
The recommended aspirin regimen varies by organization:
- ACOG and USPSTF: 81 mg/day
- WHO: 75 mg/day
- RCOG and European guidelines: 150 mg/day 1
In the United States, 81 mg is the standard recommended dose 3, 2. Aspirin should be started between 12-16 weeks of gestation (optimally before 16 weeks) for maximum effectiveness and continued daily until delivery 1, 2.
Efficacy and Timing Considerations
Starting aspirin before 16 weeks of gestation is crucial for effectiveness. Research shows that low-dose aspirin prophylaxis in high-risk women reduces:
The timing of initiation is critical - aspirin is more effective in reducing preeclampsia and intrauterine growth restriction when started before 16 weeks gestation compared to later initiation 4.
Special Populations
Autoimmune Conditions
- SLE patients: 81-100 mg daily starting in first trimester, combined with hydroxychloroquine if possible
- Obstetric APS: Low-dose aspirin combined with prophylactic-dose heparin/LMWH
- Thrombotic APS: Low-dose aspirin combined with therapeutic-dose heparin/LMWH 1
Obese Patients
Recent research suggests that higher doses (162 mg) may be more effective in obese high-risk patients. A 2025 study showed a 78% probability of benefit with 162 mg compared to 81 mg in reducing preeclampsia with severe features in obese high-risk individuals 5. However, this requires further validation before changing standard recommendations.
Safety and Contraindications
Low-dose aspirin (≤100 mg daily) is considered safe during pregnancy with minimal risk of serious maternal or fetal complications 2, 6. However, it should generally be avoided during the last 3 months of pregnancy unless specifically directed by a doctor 1.
Low-dose aspirin is not recommended for prevention of early pregnancy loss, fetal growth restriction, or stillbirth in women without other risk factors for preeclampsia 2, 6.
Emerging Evidence and Considerations
Some recent evidence suggests that doses >100 mg of aspirin daily may be more effective at reducing preeclampsia risk 7. The International Federation of Gynecology and Obstetrics recommends 150 mg of aspirin (or two 81 mg tablets as an acceptable alternative) 7. However, the current standard of care in the US remains 81 mg daily based on ACOG and USPSTF guidelines 3, 2.
Common Pitfalls to Avoid
- Starting aspirin too late (after 16 weeks) reduces effectiveness
- Discontinuing aspirin too early (before delivery)
- Not identifying all relevant risk factors when assessing patients
- Using aspirin for prevention in low-risk women without indication
- Poor patient education about medication adherence