Aspirin Use in Pregnancy
Yes, low-dose aspirin (60-160 mg daily) is safe and recommended during pregnancy for women at high risk for preeclampsia, but it should be started after 12 weeks of gestation and discontinued before delivery due to increased bleeding risks.
Who Should Take Aspirin in Pregnancy
Based on major guideline consensus 1, aspirin is indicated for pregnant women with:
High-Risk Factors (one or more warrants treatment):
- History of preeclampsia, especially early-onset (<34 weeks) or in multiple pregnancies
- Chronic hypertension
- Type 1 or 2 diabetes
- Renal disease
- Autoimmune disease (e.g., lupus, antiphospholipid syndrome)
- Multifetal gestation
Multiple Moderate-Risk Factors (several together may warrant treatment):
- First pregnancy
- Age ≥40 years
- Pregnancy interval >10 years
- BMI ≥35 kg/m²
- Family history of preeclampsia
Dosing and Timing
Dose: 60-160 mg daily (ACOG recommends 60-80 mg; WHO and NICE recommend 75-150 mg) 1
Critical timing considerations:
- Start: After 12 weeks but ideally before 16 weeks of gestation 1
- Stop: Consider discontinuation before delivery (see safety concerns below)
The evidence strongly supports that aspirin initiated before 16-20 weeks reduces preterm preeclampsia by 62% and improves birth outcomes 2, 3. Starting later significantly diminishes efficacy.
Proven Benefits
Low-dose aspirin in high-risk women reduces 1:
- Preeclampsia by 24%
- Preterm birth by 14%
- Intrauterine growth restriction by 20%
- Perinatal mortality (approaching statistical significance)
Safety Concerns: The Critical Nuance
The FDA label warns against aspirin use in the last 3 months of pregnancy 4, and this warning deserves serious attention given emerging evidence.
Maternal Bleeding Risks
Recent high-quality evidence reveals concerning bleeding complications 5, 6:
- First trimester: 2.87-fold increased hemorrhage risk 5
- Second/third trimester: 1.74-fold increased risk 5
- Postpartum hemorrhage: 1.23-1.44-fold increased risk 5, 6
- Postpartum hematoma: 2.21-fold increased risk 6
A French nationwide cohort of 5.8 million pregnancies (2015-2022) demonstrated these risks are real and clinically significant 5. The Swedish population study of 313,624 pregnancies confirmed increased intrapartum bleeding (2.9% vs 1.5%) and postpartum hemorrhage (10.2% vs 7.8%), particularly after vaginal delivery 6.
Fetal/Neonatal Risks
- Neonatal intracranial hemorrhage: 9.66-fold increased risk in one large study 6
- However, pooled trial data showed no increased risk of fetal intracranial bleeding 1
- No developmental harms identified at 18 months follow-up 1
- No increased placental abruption risk 1
Clinical Algorithm
Step 1: Identify high-risk factors at first prenatal visit
Step 2: If one or more high-risk factors present:
- Initiate 75-160 mg aspirin daily after 12 weeks (ideally before 16 weeks)
- Evening dosing may improve efficacy 2
Step 3: Continue through pregnancy BUT:
- Consider discontinuation 1-2 weeks before planned delivery to reduce bleeding risk 7, 8
- Balance against preeclampsia risk in third trimester
- Definitely stop if spontaneous labor begins
Step 4: Counsel patients about:
- Substantial preeclampsia prevention benefits
- Real but manageable bleeding risks
- Need for close monitoring near delivery
Important Caveats
Obesity reduces aspirin efficacy: Women with BMI >40 kg/m² show higher thromboxane levels and incomplete platelet inhibition, potentially requiring higher doses 2
Not for routine use: Low-risk women should NOT receive aspirin—the bleeding risks outweigh minimal benefits in this population 1
Contraindications: Aspirin allergy or previous adverse reactions 4
The timing paradox: While guidelines recommend continuation until delivery for preeclampsia prevention 1, the most recent safety data (2026) suggests discontinuation before delivery may be prudent 5, 7, 6, 8. This represents an evolving area where clinical judgment must weigh individual preeclampsia risk against hemorrhage risk.
The evidence is clear that low-dose aspirin works for preeclampsia prevention when properly targeted and timed, but recent large-scale safety data demands we reconsider the "continue until delivery" recommendation, particularly in women approaching term without active preeclampsia.