What are the risks of taking baby (acetylsalicylic acid) aspirin during pregnancy?

Risk of Baby Aspirin in Pregnancy

Low-dose aspirin (81-100 mg daily) during pregnancy is generally safe with minimal maternal or fetal risks when used appropriately, though it carries a small increased risk of bleeding complications at delivery. 1

Safety Profile for Maternal Outcomes

Low-dose aspirin does not increase most serious maternal complications:

• No increased risk of placental abruption (RR 1.17,95% CI 0.93-1.48) based on pooled analysis of 23,332 women 1
• No significant increase in postpartum hemorrhage overall (RR 1.02,95% CI 0.96-1.09) in trials of 22,760 women 1
• No effect on blood loss at delivery in most studies 1

However, recent population-based data shows modest bleeding risks:

• Increased intrapartum bleeding (2.9% vs 1.5% in non-users; adjusted OR 1.63,95% CI 1.30-2.05) 2
• Increased postpartum hemorrhage (10.2% vs 7.8%; adjusted OR 1.23,95% CI 1.08-1.39) 2
• Increased postpartum hematoma (0.4% vs 0.1%; adjusted OR 2.21,95% CI 1.13-4.34) 2
• These bleeding risks are primarily seen with vaginal delivery, not cesarean delivery 2

Fetal and Neonatal Safety

Low-dose aspirin has minimal fetal risks when used at appropriate doses:

• No increased perinatal mortality (RR 0.92,95% CI 0.76-1.11) across 22,848 pregnancies 1
• No increased neonatal intracranial hemorrhage in most studies (pooled RR 0.84,95% CI 0.61-1.16) 1
• No increased pregnancy loss, neonatal hemorrhage, or growth restriction in meta-analysis of 32,217 women 1

However, one recent Swedish study found increased neonatal intracranial hemorrhage (0.07% vs 0.01%; adjusted OR 9.66,95% CI 1.88-49.48), though absolute numbers were very small 2

Congenital Anomaly Concerns

First trimester exposure carries theoretical but uncertain risks:

• Possible increased risk of gastroschisis (OR 2.37,95% CI 1.44-3.88) with first trimester exposure, though the American College of Chest Physicians notes this estimate has "questionable validity" due to significant bias in contributing studies 1
• Uncertain miscarriage risk when taken around conception, though meta-analyses of randomized trials failed to establish increased risk (RR 0.92,95% CI 0.71-1.19 for first/second trimester; RR 1.3,95% CI 0.63-2.69 for first trimester only) 1

Long-Term Developmental Outcomes

No evidence of harm to child development:

• No differences in physical or mental developmental outcomes at 18 months (gross motor development, height, weight, hospital visits) in the largest trial follow-up 1
• No increased cryptorchidism in male infants exposed in utero 1

Critical Timing and Dosing Considerations

Safety depends on appropriate use:

• Doses ≤100 mg daily are considered safe 3
• Should be initiated between 12-28 weeks gestation (optimally before 16 weeks) for preeclampsia prevention 1, 4, 5
• The FDA label warns against use in the last 3 months of pregnancy unless directed by a physician due to potential problems in the unborn child or delivery complications 6

Special Contraindications

Aspirin should be discontinued in specific situations:

• Aspirin desensitization therapy for aspirin-exacerbated respiratory disease (AERD) must be discontinued prior to planned pregnancy or immediately upon pregnancy confirmation due to unacceptable fetal risks, particularly premature ductus arteriosus closure, intrauterine growth restriction, and perinatal mortality 1
• This differs from low-dose aspirin for preeclampsia prevention, which uses much lower doses 1

Clinical Context for Risk-Benefit Assessment

The benefits typically outweigh risks when appropriately indicated:

• For high-risk women (history of preeclampsia, chronic hypertension, diabetes, renal disease, autoimmune disease), low-dose aspirin reduces preeclampsia, preterm birth, and intrauterine growth restriction 1, 4, 5
• The U.S. Preventive Services Task Force concluded with "moderate certainty that the magnitude of net benefit is substantial" for high-risk women 1
• Minor adverse events (throat itching, epigastric pain) occasionally cause treatment discontinuation but are uncommon 1

When prescribing aspirin during pregnancy, the small increased bleeding risks at delivery must be weighed against the substantial benefits for preventing life-threatening preeclampsia in appropriate candidates. 2