What are the moderate risk factors for preeclampsia (high blood pressure during pregnancy) prophylaxis?

From the Guidelines

Women with moderate risk factors for preeclampsia, such as nulliparity, maternal age over 35 years, BMI greater than 30 kg/m², family history of preeclampsia, and pregnancy interval greater than 10 years, should be prescribed low-dose aspirin (81-150 mg daily) starting between 12-16 weeks of gestation and continuing until delivery. The optimal timing for initiation is before 16 weeks when placentation is still occurring, as this is when aspirin can most effectively modify the pathophysiological process that leads to preeclampsia 1.

Key Considerations

• The medication should be taken at bedtime for maximum effectiveness, as there is a circadian variation in aspirin's antiplatelet effects.
• Aspirin works by inhibiting platelet cyclooxygenase, reducing thromboxane production while preserving prostacyclin, thereby improving placental blood flow and reducing the risk of the endothelial dysfunction that characterizes preeclampsia.
• This prophylaxis can reduce preeclampsia risk by approximately 10-15% in women with moderate risk factors, as supported by the U.S. Preventive Services Task Force recommendation statement 1.
• No laboratory monitoring is required during this preventive therapy.

Clinical Guidelines

• The American Heart Association and the American Stroke Association recommend that women with chronic primary or secondary hypertension or previous pregnancy-related hypertension take low-dose aspirin from 12 weeks until delivery 1.
• The American Academy of Family Physicians recommends low-dose aspirin (81 mg/d) after 12 weeks of gestation in women who are at high risk for preeclampsia 1.
• The National Institute for Health and Care Excellence recommends that women at high risk for preeclampsia take 75 mg/d of aspirin from 12 weeks until delivery, and also recommends the same for women with more than 1 moderate-risk factor 1.

Recent Evidence

• A 2022 systematic review of international clinical practice guidelines for pregnancy hypertension found that all guidelines recommended low-dose aspirin for preeclampsia prevention, although the indications, dosage, and timing varied 1.
• The review highlighted the importance of early initiation of aspirin, optimally before 16 weeks, and continuation until delivery.

From the Research

Moderate Risk Factors for Preeclampsia Prophylaxis

• The American College of Obstetricians and Gynecologists recommends low-dose aspirin prophylaxis for women with more than one of several moderate risk factors for preeclampsia 2.
• Moderate risk factors for preeclampsia include first pregnancy, maternal age of 35 years or older, a body mass index greater than 30, family history of preeclampsia, sociodemographic characteristics, and personal history factors 2.
• The Society for Maternal-Fetal Medicine Special Statement presents checklists intended to reduce the chance that risk factors might be inadvertently overlooked and to improve the probability of aspirin being recommended for all appropriate candidates 3.
• Despite recommendations, low-dose aspirin use is reported in <50% of patients with high-risk factors and <25% of patients with >1 moderate-risk factor, representing an important "quality gap" and demonstrating the need for quality improvement activities 4.
• A study examined adherence to aspirin for preeclampsia prophylaxis and found that among participants who recalled aspirin recommendation, adherence was similar between high-risk (81.7%) and moderate-risk (76.9%) groups 5.

Aspirin Prophylaxis Guidelines

• The American College of Obstetricians and Gynecologists recommends daily low-dose aspirin (81 mg/day) prophylaxis in women at high risk of preeclampsia, initiated between 12 weeks and 28 weeks of gestation (optimally before 16 weeks) and continued daily until delivery 2.
• The World Health Organization recommends that 75 mg of aspirin should be initiated before 20 weeks of gestation for women at high risk of preeclampsia 6.
• The Royal College of Obstetricians and Gynaecologists recommends 150 mg of aspirin daily, and the National Institute of Health and Care Excellence guidelines suggest risk stratification with a dosage of 75 mg for those at moderate risk of preeclampsia and 150 mg for those at high risk of preeclampsia 6.

Quality Improvement Opportunities

• Quality improvement activities are needed to increase the use of aspirin by patients with risk factors for preeclampsia 4.
• A process metric to standardize the measurement of the rate of aspirin use can help identify areas for improvement 4.
• Patient education and counseling are crucial to improve adherence to aspirin prophylaxis recommendations 5.