Prenatal Aspirin Indications
Low-dose aspirin (81 mg daily) should be prescribed for pregnant women with at least one high-risk factor for preeclampsia OR more than one moderate-risk factor, initiated between 12-28 weeks of gestation (optimally before 16 weeks) and continued until delivery. 1, 2
High-Risk Factors (One or More Qualifies)
Women with any single high-risk factor should receive aspirin prophylaxis:
- History of preeclampsia, especially with preterm delivery <34 weeks 1, 2
- Multifetal gestation (twins, triplets, etc.) 1, 2
- Chronic hypertension 1, 2
- Type 1 or Type 2 diabetes mellitus 1, 2
- Renal disease 1, 2
- Autoimmune disease (systemic lupus erythematosus, antiphospholipid syndrome) 1, 2
Moderate-Risk Factors (Two or More Required)
Women need at least two moderate-risk factors to warrant aspirin:
- Nulliparity (first pregnancy) 1, 2
- Maternal age ≥35 years 1, 2
- Body mass index >30 1, 2
- Family history of preeclampsia (mother or sister) 1, 2
- Pregnancy interval >10 years 3
- Sociodemographic characteristics (African American race, low socioeconomic status) 1, 2
Dosing and Timing
Standard U.S. practice: 81 mg daily, initiated between 12-28 weeks (optimally before 16 weeks), continued until delivery 1, 2. Recent evidence suggests higher doses (100-162 mg) may be more effective, particularly in women with obesity, multifetal gestation, or prior severe preeclampsia 4, 5, though 81 mg remains the guideline-recommended dose in the United States.
Critical timing consideration: Initiation before 16 weeks appears essential for maximal benefit, as aspirin works by improving early placental implantation 4, 6.
Important Caveats
Chronic hypertension alone warrants aspirin based on current guidelines 1, 2, though one 2020 retrospective study found no reduction in superimposed preeclampsia rates with aspirin in this population 7. Despite this conflicting evidence, the guideline recommendation remains in place because chronic hypertension is an established high-risk factor.
Do NOT prescribe aspirin for: Prevention of early pregnancy loss, fetal growth restriction, stillbirth, or preterm birth in the absence of preeclampsia risk factors—current evidence does not support benefit for these indications 1, 2.
Safety profile: Low-dose aspirin (81 mg) is generally safe in pregnancy with low risk of maternal or fetal complications 1, 2. However, recent large cohort data suggest a small excess risk of maternal hemorrhagic complications 6, reinforcing the importance of restricting use to appropriate high-risk populations rather than universal prophylaxis.
Adherence matters: Aspirin response varies by patient factors including obesity, diabetes, and age 8. Women with obesity or diabetes may have reduced platelet inhibition and potentially require higher doses, though this remains investigational 5, 8.