What are the indications for low-dose (acetylsalicylic acid) aspirin in pregnancy?

Indications for Low-Dose Aspirin in Pregnancy

Low-dose aspirin (81 mg/day) prophylaxis is recommended for pregnant women at high risk of preeclampsia and should be initiated between 12-16 weeks of gestation and continued daily until delivery. 1, 2, 3

High-Risk Factors (Single Factor Sufficient for Aspirin Prophylaxis)

• History of preeclampsia, especially early-onset preeclampsia with delivery <34 weeks
• Multifetal gestation
• Chronic hypertension
• Type 1 or type 2 diabetes
• Renal disease
• Autoimmune diseases (such as systemic lupus erythematosus or antiphospholipid syndrome)

Moderate-Risk Factors (Multiple Factors Required for Aspirin Prophylaxis)

Aspirin prophylaxis should be considered when multiple moderate risk factors are present:

• First pregnancy (nulliparity)
• Maternal age ≥35 years
• BMI >30 kg/m²
• Family history of preeclampsia (mother or sister)
• Sociodemographic characteristics (low socioeconomic status)
• Personal history factors

Dosing and Timing

• The recommended dose is 81 mg daily according to ACOG and USPSTF 1, 2
• Alternative dosing recommendations include:
  • WHO: 75 mg/day
  • RCOG: 150 mg/day 1
• Initiation should occur between 12-16 weeks of gestation (optimally before 16 weeks) 1, 2, 3
• Therapy should continue until delivery 1

Clinical Benefits

Low-dose aspirin prophylaxis in high-risk women has been shown to:

• Reduce preeclampsia risk by 24% 4, 1
• Reduce preterm birth risk by 14% 4, 1
• Reduce intrauterine growth restriction by 20% 4, 1

Safety Considerations

• Low-dose aspirin during pregnancy is considered safe with minimal risk of serious maternal or fetal complications 2, 3
• The FDA notes that aspirin should generally be avoided during the last 3 months of pregnancy unless specifically directed by a doctor, as it may cause problems in the unborn child or complications during delivery 5
• However, in the specific context of preeclampsia prevention, the benefits of continuing low-dose aspirin until delivery outweigh the risks 1

Important Clinical Caveats

1. Aspirin prophylaxis is most effective when started before 16 weeks of gestation 1, 6
2. Despite ACOG recommendations, studies have shown mixed results regarding efficacy in all high-risk groups 4, 7
3. In the absence of high-risk factors for preeclampsia, current evidence does not support prophylactic low-dose aspirin for prevention of early pregnancy loss, fetal growth restriction, stillbirth, or preterm birth 2, 3
4. Patient education about medication adherence is crucial for effective preeclampsia prevention 1

Risk Assessment Algorithm

1. Evaluate for presence of any high-risk factors
   • If ≥1 high-risk factor present → prescribe low-dose aspirin (81 mg daily)
2. If no high-risk factors, evaluate for moderate-risk factors
   • If ≥2 moderate-risk factors present → prescribe low-dose aspirin (81 mg daily)
3. Initiate therapy between 12-16 weeks gestation
4. Continue therapy until delivery
5. Monitor for adherence and any adverse effects

This approach aligns with current ACOG and USPSTF guidelines to identify women who would benefit most from preeclampsia prevention with low-dose aspirin.