The impact of risk factors on aspirin\u27s efficacy for the prevention of preterm birth

Background: The ASPIRIN Trial was a landmark study that demonstrated a reduction in preterm birth (PTB) and hypertensive disorders of pregnancy (HDP) in nulliparous women who received low-dose aspirin (LDA). All women in the study had at least one moderate-risk factor for preeclampsia, nulliparity. Unlike current United States Preventative Service Task Force (USPSTF) guidelines, which recommend LDA for two or more moderate-risk factors, women in this study were randomized to receive LDA regardless of the presence or absence of an additional risk factor. Objective: To compare how low-dose aspirin (LDA) differentially benefits nulliparous women with and without additional preeclampsia risk factors for the prevention of preterm birth (PTB) and hypertensive disorders of pregnancy (HDP). Study design: This is a non-pre-specified secondary analysis of the ASPIRIN trial that randomized nulliparous women with singleton pregnancies from six low-middle income countries to receive LDA or placebo. Our primary exposure was having an additional preeclampsia risk-factor beyond nulliparity. Our primary outcome was PTB before 37 weeks and our secondary outcomes included PTB before 34 weeks, PTB before 28 weeks, HDP, and perinatal mortality. Results: Among 11,558 nulliparous women who met the inclusion criteria, 66.8% had no additional risk factors. LDA similarly reduced the risk of PTB (RR 0.75 vs. 0.85, p=0.35). Additionally for our secondary outcomes, LDA similarly reduced the risk of PTB \u3c28 \u3eweeks, HDP, and perinatal mortality in women with and without additional risk factors. The reduction of PTB (RR 0.69 vs. 1.04, p=0.04). Conclusion: LDA\u27s ability to prevent PTB, HDP, and perinatal mortality is similar in nulliparous women with and without additional risk factors. Professional societies should consider recommending LDA to all nulliparous wome