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A study examining aspirin doses of 150 to 160 mg and 75 mg for preeclampsia prevention found no clinically important difference between groups.

The risk of developing preeclampsia or postpartum bleeding complications did not differ in women who used 150 to 160 mg of aspirin vs 75 mg for preeclampsia prevention during pregnancy, according to a study published in JAMA Network Open.

“Our findings suggest that either dose may be a reasonable choice when using aspirin to prevent preeclampsia,” Lina Bergman, PhD, and colleagues wrote.

The nationwide cohort study included 13,828 women who gave birth between 2017 and 2020 and used low-dose aspirin during pregnancy due to an increased risk for preeclampsia. Researchers grouped the women by the dose prescribed (75 mg or 150-160 mg) and investigated rates of preeclampsia and, as a safety outcome, postpartum hemorrhage.

Among the women, a third were prescribed 150 to 160 mg of aspirin, and the remaining two-thirds were prescribed 75 mg. Three-quarters of the study population filled at least two of the aspirin prescriptions.

Preeclampsia Based on Aspirin, Patient Characteristics

“An increasing number of international guidelines recommend aspirin at a dosage of 100 mg or above for preeclampsia prevention,” the researchers wrote. “Our study does not provide evidence supporting the superiority of higher doses over lower doses.”

According to the study, the rate of preeclampsia in women using 150 to 160 mg of aspirin was 9.5% compared with 8.9% in women using 75 mg of aspirin. The adjusted relative risk for preeclampsia with the higher dose was 1.07.

Moreover, preeclampsia rates did not differ by timing of birth. Full-term preeclampsia occurred in 6.7% of women using 150 to 160 mg and 6.1% using 75 mg. Preeclampsia with preterm birth at less than 37 weeks’ gestation occurred in 2.8% in each group. Preeclampsia with preterm birth at less than 34 weeks’ gestation occurred in 0.8% of women taking the higher aspirin dose compared with 1.1% taking the lower dose.

“Lastly, there was no difference in the risk of developing preeclampsia with small for gestational age infants (53 patients [1.1%] vs 98 patients [1.1%]),” Dr. Bergman and colleagues noted.

Directions for Future Research

Despite concerns that higher aspirin doses could lead to increased risk of postpartum hemorrhage, the study found no clinically important difference between groups. Rates of postpartum hemorrhage were 6.9% in the higher-dose group compared with 6.4% in the 75-mg group.

“However, large, randomized trials investigating aspirin dose in pregnancy are still needed,” the researchers advised.