Research in context
Evidence before this study
We searched PubMed for articles published in English on low-dose aspirin therapy in pregnancy for improvement of birth outcomes, published between Jan 1, 2000 and Sept 27, 2019, using the search terms “aspirin” AND “pregnancy” OR “hypertensive disease” OR “preterm birth” OR “preeclampsia”. A secondary analysis of the Maternal-Fetal Medicine Units Network trial of aspirin and a single trial of preconception aspirin (the EAGeR trial) suggested a reduced risk of preterm birth among women who received low-dose aspirin compared with a placebo control. Meta-analyses and systematic reviews of trials of low-dose aspirin in pregnant women to prevent pre-eclampsia have suggested that the occurrence of preterm birth is reduced in women receiving aspirin, with this effect possibly increased when low-dose aspirin is started early in pregnancy.
Added value of this study
This study is the first large trial of low-dose aspirin initiated early in pregnancy with the prevention of preterm birth as the primary outcome. This trial was designed to test the hypothesis that low-dose aspirin (81 mg) administered daily and initiated in the first trimester reduces the incidence of preterm delivery in nulliparous women with a singleton pregnancy. Additionally, our data suggested that the intervention is safe for women across the six low-income and middle-income countries (LMICs) that were represented in the trial.
Implications of all the available evidence
This trial confirms the previously suggested benefit of low-dose aspirin in reducing the risk of preterm birth. Nulliparous women with a singleton pregnancy who were allocated to low-dose aspirin in early pregnancy (between 6 weeks and 0 days of gestation and 13 weeks and 6 days of gestation, until 36 weeks) were 11% less likely to deliver before 37 weeks. In addition, low-dose aspirin reduced the risk of early preterm delivery (before 34 weeks) by 25%, and perinatal mortality by 14%. These outcomes are consistent with previous meta-analyses that showed similar reductions in preterm birth and perinatal mortality. Because of the large sample size, this trial was able to show these benefits definitively in a diverse group of women from various LMICs. The low cost and proven tolerability of aspirin in this population suggests that our aspirin regimen can be readily and safely adopted across a range of clinical sites globally.