The impact of low-dose aspirin on preterm birth: secondary analysis of a randomized controlled trial

The objective of this study is to determine whether low-dose aspirin (LDA) reduced the rate of preterm birth (PTB) in a cohort of women at high risk for preeclampsia.

Secondary analysis of the Maternal-Fetal Medicine Units High-Risk Aspirin trial. Preterm births were categorized by phenotype: indicated, spontaneous or due to preterm premature rupture of membranes (PPROMs).

Of 1789 randomized women, 30.5% delivered before 37 weeks (18.5% indicated, 5.8% spontaneous and 6.2% following preterm PPROMs). Among women randomized to LDA, we observed a trend favoring fewer PTBs due to spontaneous preterm labor and preterm PPROMs, odds ratio (OR: 0.826 (0.620, 1.099)); the incidence of indicated PTBs appeared unchanged, OR: 0.999 (0.787, 1.268).

Although not reaching significance, we observed an effect size similar to other studies of both low- and high-risk women. These results support findings from other studies assessing LDA as a PTB prevention strategy.