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 0.73−1.09) and less than 34 weeks (RR 0.62, 95% CI 0.37−1.05) 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: 0.35−0.59), as did, to a lower magnitude, those who began aspirin 100 mg daily after 16 weeks (RR: 0.88, 95% CI: 0.80−0.97). 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 and 81 mg of daily aspirin (RR: 0.39, 95% CI: 0.31−0.48). 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.