Background: The daily use of low-dose aspirin may be a safe, widely available, and inexpensive intervention for reducing the risk of preterm birth. Data on the potential side effects of low-dose aspirin use during pregnancy in low- and middle-income countries are needed.Objective: This study aimed to assess differences in unexpected emergency medical visits and potential maternal side effects from a randomized, double-blind, multicountry, placebo-controlled trial of low-dose aspirin use (81 mg daily, from 6 to 36 weeks\u27 gestation).Study design: This study was a secondary analysis of data from the Aspirin Supplementation for Pregnancy Indicated Risk Reduction In Nulliparas trial, a trial of the Global Network for Women\u27s and Children\u27s Health conducted in India (2 sites), Pakistan, Guatemala, Democratic Republic of the Congo, Kenya, and Zambia. The outcomes for this analysis were unexpected emergency medical visits and the occurrence of the following potential side effects-overall and separately-nausea, vomiting, rash or hives, diarrhea, gastritis, vaginal bleeding, allergic reaction, and any other potential side effects. Analyses were performed overall and by geographic region.Results: Between the aspirin (n=5943) and placebo (n=5936) study groups, there was no statistically significant difference in the risk of unexpected emergency medical visits or the risk of any potential side effect (overall). Of the 8 potential side effects assessed, only 1 (rash or hives) presented a different risk by treatment group (4.2% in the aspirin group vs 3.5% in the placebo group; relative risk, 1.20; 95% confidence interval, 1.01-1.43; P=.042).Conclusion: The daily use of low-dose aspirin seems to be a safe intervention for reducing the risk of preterm birth and well tolerated by nulliparous pregnant women between 6 and 36 weeks\u27 gestation in low- and middle-income countries
