Indications for Aspirin During Pregnancy
Low-dose aspirin should be prescribed to pregnant women at high risk for preeclampsia, starting between 12-16 weeks of gestation and continuing until delivery, with a dose of 100-150 mg daily (or 162 mg using available 81 mg tablets in the U.S.) for those with diabetes, and 81 mg daily for other high-risk conditions. 1, 2
High-Risk Factors Requiring Aspirin Prophylaxis
Women with any one of the following high-risk factors should receive aspirin:
- History of preeclampsia in a prior pregnancy, particularly early-onset preeclampsia with delivery before 34 weeks 2, 3, 4
- Type 1 or type 2 diabetes (pregestational) 1, 2, 3, 4
- Chronic hypertension 2, 3, 4
- Renal disease 2, 3, 4
- Autoimmune disease (such as systemic lupus erythematosus or antiphospholipid syndrome) 2, 3, 4
- Multifetal gestation (twins, triplets, etc.) 2, 3, 4
Moderate-Risk Factors
Women with two or more of the following moderate-risk factors should be considered for aspirin prophylaxis:
- Nulliparity (first pregnancy) 2, 3, 4
- Maternal age ≥35 years 2, 3, 4
- Body mass index (BMI) >30 kg/m² (obesity) 2, 3, 4
- Family history of preeclampsia (mother or sister) 2, 3, 4
- Low socioeconomic status 2
- Interpregnancy interval ≥10 years 2
Dosing Recommendations
For Women with Diabetes
100-150 mg daily is required for pregnant women with type 1 or type 2 diabetes, as the standard 81 mg dose has been shown to be insufficient 1, 2. The American Diabetes Association specifically recommends this higher dose because diabetes is an independent risk factor for preeclampsia and meta-analyses demonstrate that doses below 100 mg are not effective 1.
For Other High-Risk Women
81 mg daily is the standard dose recommended by the U.S. Preventive Services Task Force for most high-risk women without diabetes 1, 3, 4. However, evidence suggests that higher doses (100-150 mg) may be more effective overall 2, 5.
Special Consideration for Obesity
Women with BMI >40 kg/m² may require dose adjustment, as higher BMI may reduce aspirin's effectiveness 2. Recent evidence suggests that 162 mg daily (two 81 mg tablets) may be more beneficial than 81 mg in obese high-risk women, with a 78% probability of reducing preeclampsia with severe features 6.
Timing of Initiation and Duration
- Start between 12-16 weeks of gestation (optimally before 16 weeks) for maximum effectiveness 1, 2, 3, 4
- Continue daily until delivery 2, 3, 4
- Earlier initiation (before 12 weeks) may be considered, as defective placentation occurs in the first trimester and aspirin can improve uteroplacental blood flow during this critical period 5, 7
Safety Profile
Low-dose aspirin in pregnancy is safe and does not increase the risk of:
- Placental abruption 2, 5
- Postpartum hemorrhage 2, 5
- Fetal intracranial bleeding 2, 5
- Congenital anomalies 2, 3, 4
- Perinatal mortality 5
Additional Benefits Beyond Preeclampsia Prevention
Aspirin prophylaxis provides:
- 24% reduction in preeclampsia risk in high-risk women 5
- 14% reduction in preterm birth 5
- 20% reduction in intrauterine growth restriction (IUGR) 5
- Increased mean birthweight by approximately 130 grams 5
Important Caveats
- Do not use aspirin in the last 3 months of pregnancy unless specifically directed by a physician, per FDA labeling, as it may cause problems in the unborn child or complications during delivery 8
- In the absence of high-risk factors, aspirin is not recommended for prevention of early pregnancy loss, fetal growth restriction, stillbirth, or preterm birth 3, 4
- Women with chronic hypertension alone may have reduced effectiveness with standard 81 mg dosing and should be considered for higher doses 2