Low-dose aspirin use in low-risk nulliparous pregnancies: a systematic review and meta-analysis of randomized controlled trials.

Objective: To assess the efficacy of low-dose aspirin in the prevention of adverse outcomes in low-risk, nulliparous singleton pregnancies.

Data Sources: PubMed, Ovid MEDLINE, Scopus, Cochrane Library, clinicaltrials.gov, and ScienceDirect were searched from their inception to August 5, 2023.

Eligibility Criteria For Selecting Studies: Randomized clinical trials comparing low-dose aspirin with placebo or with no treatment in low-risk nulliparous singleton pregnancies were included. High-risk pregnancies, including prior preterm birth, prior preeclampsia, and those affected by maternal diabetes or chronic hypertension were excluded.

Data Appraisal And Synthesis Methods: The primary outcome was the incidence of preterm delivery at less than 37 weeks. The summary measures were reported as relative risk (RR) or as mean difference (MD) with a 95% confidence interval (CI).

Results: Ten trials, including 27,075 nulliparous low-risk pregnancies, were included. Overall, low-dose aspirin was associated with no significant differences in preterm birth less than 37 weeks (RR 0.90, 95% CI 0.73 to 1.09) and less than 34 weeks (RR 0.62, 95% CI 0.37 to 1.05) compared to control . Patients who took 100 mg daily of aspirin prior to 16 weeks had a significantly lower risk of preterm birth at less than 37 weeks (RR 0.45, 95% CI 0.35 to 0.59), as did, to a lower magnitude, those who began aspirin 100mg daily after 16 weeks (RR 0.88, 95% CI 0.80 to 0.97). Those who took 100 mg daily of aspirin were at a lower risk of preterm birth at less than 37 weeks than those who took between 60-81 mg of daily aspirin (RR 0.39, 95% CI 0.31 to 0.48). No statistically significant differences were found in the incidence of hypertensive disorders of pregnancy, perinatal or neonatal death.

Conclusions: Low-dose aspirin at 100 mg daily reduces the incidence of preterm birth at less than 37 weeks in low-risk, nulliparous pregnancies and may be most helpful if initiated prior to 16 weeks.