Low-Dose Aspirin for Prevention of Preeclampsia in Pregnancy
Low-dose aspirin (81 mg/day) is strongly recommended for pregnant women at high risk of preeclampsia and should be initiated between 12-28 weeks of gestation (optimally before 16 weeks) and continued daily until delivery. 1
Risk Assessment and Eligibility
The U.S. Preventive Services Task Force (USPSTF) and American College of Obstetricians and Gynecologists (ACOG) recommend low-dose aspirin for women with:
High-Risk Factors (one or more):
- History of preeclampsia, especially with early onset (<34 weeks)
- Multifetal gestation
- Chronic hypertension
- Type 1 or 2 diabetes
- Renal disease
- Autoimmune disease (such as lupus or antiphospholipid syndrome)
Moderate-Risk Factors (more than one):
- First pregnancy (nulliparity)
- Age ≥35 years
- BMI >30 kg/m²
- Family history of preeclampsia (mother or sister)
- Sociodemographic characteristics (African American race, low socioeconomic status)
- Personal history factors (previous adverse pregnancy outcome, >10-year pregnancy interval)
Dosing and Timing
- Dose: 81 mg daily (standard low-dose aspirin tablet in the US)
- Initiation: Between 12-28 weeks of gestation, optimally before 16 weeks
- Duration: Continue until delivery
While studies have used dosages between 60-150 mg/day, the most commonly available form in the US is 81 mg, which is considered appropriate for prophylaxis 1. Starting earlier (before 16 weeks) may be more beneficial for improving placentation, though evidence shows benefit even when started later 2.
Evidence of Benefit
Low-dose aspirin has been shown to:
- Reduce preeclampsia risk by 24% in clinical trials 1
- Reduce preterm birth risk by 14% 1
- Reduce intrauterine growth restriction (IUGR) by 20% 1
These benefits are particularly significant for women with high-risk factors. The mechanism involves balancing thromboxane A2 and prostacyclin levels, which helps maintain adequate uteroplacental blood flow and improves placentation 2.
Safety Profile
The USPSTF found adequate evidence that low-dose aspirin during pregnancy does not increase the risk of:
- Placental abruption
- Postpartum hemorrhage
- Fetal intracranial bleeding
- Perinatal mortality 1
Daily low-dose aspirin use in pregnancy is considered safe with a low likelihood of serious maternal or fetal complications 3, 4.
Recent Developments and Nuances
Recent research suggests that in women at high risk for preeclampsia who have normal biomarkers (sFlt-1:PlGF ratio ≤38) at 24-28 weeks, discontinuing aspirin at that point may be as effective as continuing until 36 weeks 5. However, this approach requires specialized biomarker testing that may not be widely available.
It's worth noting that a 2020 study found that despite ACOG guideline implementation, low-dose aspirin did not significantly reduce superimposed preeclampsia in women with chronic hypertension 1. This highlights that while aspirin is beneficial overall, its effectiveness may vary in specific high-risk subgroups.
Common Pitfalls to Avoid
Delayed initiation: Starting aspirin after 16 weeks may reduce its effectiveness in preventing the early placentation defects that lead to preeclampsia.
Inconsistent use: Daily administration is crucial for maintaining the antiplatelet effect.
Using aspirin for non-indicated pregnancies: In the absence of high-risk factors for preeclampsia, evidence does not support using prophylactic low-dose aspirin for prevention of early pregnancy loss, fetal growth restriction, stillbirth, or preterm birth 4.
Stopping too early: Unless biomarker testing indicates otherwise, aspirin should be continued until delivery to maximize protective effects.
Inappropriate dosing: Higher doses are not recommended and may increase bleeding risk without additional benefit.
Low-dose aspirin represents one of the few effective pharmacological interventions for preventing preeclampsia, a condition with significant maternal and fetal morbidity and mortality. Its use should be strongly considered in all pregnant women meeting high-risk criteria.