Should a newly pregnant woman take aspirin (acetylsalicylic acid)?

Should a Newly Pregnant Woman Take Aspirin?

Not all newly pregnant women should take aspirin—only those at high risk for preeclampsia should receive low-dose aspirin starting between 12-16 weeks of gestation and continuing until delivery. 1, 2, 3

Risk Stratification: Who Needs Aspirin?

High-Risk Factors (Any ONE qualifies for aspirin prophylaxis):

• History of preeclampsia, especially with delivery <34 weeks 2, 3
• Multifetal gestation (twins, triplets, etc.) 2, 3
• Chronic hypertension 4, 2, 3
• Type 1 or type 2 diabetes 4, 2, 3
• Renal disease 2, 3
• Autoimmune disease (SLE, antiphospholipid syndrome) 4, 2, 3

Moderate-Risk Factors (TWO OR MORE qualify for aspirin prophylaxis):

• First pregnancy 2, 3
• Maternal age ≥35 years 1, 2, 3
• BMI >30 kg/m² 2, 3
• Family history of preeclampsia 1, 2, 3
• Low socioeconomic status 1
• Interpregnancy interval ≥10 years 1

Women without these risk factors should NOT routinely take aspirin during pregnancy. 2, 3

Dosing Recommendations

Standard Dosing for Most High-Risk Women:

• 81-100 mg daily is the standard U.S. recommendation 1, 2, 3
• However, emerging evidence suggests this dose may be suboptimal 5, 6

Higher Dosing for Specific Populations:

• 100-150 mg daily for women with type 1 or type 2 diabetes 4, 1
• 100-150 mg daily may be more effective than 81 mg for preventing preeclampsia 4, 1, 5, 6
• Consider 150-162 mg daily for women with chronic hypertension or BMI >40 kg/m², as standard 81 mg dosing has shown no benefit in these populations 1, 5

Critical caveat: The standard 81 mg dose does NOT reduce preeclampsia in women with chronic hypertension (34.3% without aspirin vs 35.5% with aspirin, p=0.79), and severe preeclampsia features actually increased (21.7% vs 31.0%, p=0.03) in one study. 1

Timing: When to Start and Stop

Initiation:

• Start between 12-16 weeks of gestation for maximum effectiveness 4, 1, 2, 3
• Can be initiated up to 28 weeks, but efficacy decreases with later initiation 1, 2, 3
• Starting before 16 weeks is optimal, as defective placentation occurs in the first trimester 1

Duration:

• Continue daily until delivery 4, 1, 2, 3
• Do not discontinue in the third trimester 1

Benefits and Safety Profile

Proven Benefits:

• 24% reduction in preeclampsia risk 1, 7
• 14% reduction in preterm birth 1, 7
• 20% reduction in intrauterine growth restriction 1, 7
• Increases mean birthweight by approximately 130g 7
• Number needed to treat: 42 women to prevent one case of preeclampsia 7

Safety:

• Low-dose aspirin does NOT increase risks of: 1, 7, 2, 3
  • Placental abruption
  • Postpartum hemorrhage
  • Fetal intracranial bleeding
  • Perinatal mortality
  • Congenital anomalies

FDA Warning:

• The FDA label cautions against aspirin use during the last 3 months of pregnancy unless directed by a physician, as it may cause problems in the unborn child or complications during delivery 8
• However, this warning applies to higher doses used for pain relief, not the low doses (81-150 mg) used for preeclampsia prevention 1, 2, 3

Common Pitfalls to Avoid

1. Don't prescribe aspirin to all pregnant women—only those meeting high-risk or moderate-risk criteria benefit 2, 3

2. Don't use 81 mg for women with chronic hypertension—consider higher doses (150-162 mg) as standard dosing is ineffective in this population 1, 5

3. Don't start aspirin too late—initiation after 16 weeks reduces effectiveness 1, 5, 6

4. Don't stop aspirin in the third trimester—continue until delivery for sustained benefit 1, 2, 3

5. Don't underdose women with diabetes—they require 100-150 mg daily, not 81 mg 4, 1