Background

Low-dose aspirin has been used during pregnancy most commonly to prevent or delay the onset of preeclampsia 1. The previous recommendation from the American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal Medicine (SMFM), and the U.S. Preventive Services Task Force (USPSTF) has been for low-dose aspirin (81 mg/d) prophylaxis after 12 weeks of gestation in pregnant individuals at high risk of preeclampsia and suggested low-dose aspirin prophylaxis in pregnant individuals with more than one moderate-risk factor 1,2. ACOG and SMFM also have provided more detailed information around timing, recommending that low-dose aspirin be initiated between 12 weeks and 28 weeks of gestation (optimally before 16 weeks) and continued daily until delivery 1.

USPSTF 2021 Recommendation

In September 2021, the USPSTF published updated recommendations on aspirin use to prevent preeclampsia and related morbidity and mortality 3. The recommendations continue to be based on only risk factors that can be obtained from a patient’s medical history. The primary USPSTF recommendation remains largely unchanged: prescribe low-dose (81 mg/d) aspirin after 12 weeks of gestation to individuals who are at high risk for preeclampsia (Grade B). However, the USPSTF provided updated guidance regarding moderate-risk factors. Specifically, the USPSTF now recommends low-dose aspirin for individuals with more than one moderate-risk factor. Additionally, the USPSTF added one new moderate-risk factor, “In vitro conception,” and modified the previous “Sociodemographic characteristics” risk factor by splitting it into two distinct factors: “Black persons (due to social, rather than biological, factors)” and “lower income.” The USPSTF notes that “Black persons” and “lower income” are associated with increased risk due to environmental, social, and historical inequities shaping health exposures, access to health care, and the unequal distribution of resources, not biological propensities; low-dose aspirin can be considered without any additional moderate-risk factor if the patient has either of these risk factors 3.

Updated ACOG and SMFM Recommendation

Based on the updated USPSTF guidance and its supporting evidence, ACOG and SMFM are revising their recommendation regarding low-dose aspirin prophylaxis for the prevention of preeclampsia. Low-dose aspirin (81 mg/d) prophylaxis is recommended for:

• Pregnant individuals at high risk of preeclampsia with one or more of the following risk factors:
  • History of preeclampsia, especially when accompanied by an adverse outcome
  • Multifetal gestation
  • Chronic hypertension
  • Pregestational type 1 or 2 diabetes
  • Kidney disease
  • Autoimmune disease (ie, systemic lupus erythematous, antiphospholipid syndrome)
  • Combinations of multiple moderate-risk factors

These risk factors are consistently associated with the greatest risk for preeclampsia. Preeclampsia incidence would likely be at least 8% in a population of pregnant individuals having one of these risk factors.

• Pregnant individuals with more than one of several moderate risk factors:
  • Nulliparity
  • Obesity (ie, body mass index > 30)
  • Family history of preeclampsia (ie, mother or sister)
  • Black race (as a proxy for underlying racism)
  • Lower income
  • Age 35 years or older
  • Personal history factors (eg, low birth weight or small for gestational age, previous adverse pregnancy outcome, >10-year pregnancy interval)
  • In vitro fertilization

These factors are independently associated with moderate risk for preeclampsia, some more consistently than others. A combination of multiple moderate-risk factors may place a pregnant person at higher risk for preeclampsia.

Additionally, low-dose aspirin can be considered if the patient has one or more of the following moderate-risk factors: Black race (as a proxy for underlying racism), or lower income. The underlying risk to health is racism and not race. However, there are not yet adequate tools for measuring the known impact of racism on health. Therefore, in this document, Black race serves as a proxy for underlying racism. These factors are associated with increased risk due to environmental, social, structural, and historical inequities shaping health exposures, access to health care, and the unequal distribution of resources, not biological propensities.

When recommended, low-dose aspirin should be initiated between 12 weeks and 28 weeks of gestation (optimally before 16 weeks) and continued daily until delivery 1.