The effectiveness of 100 mg aspirin in preventing superimposed preeclampsia in women with chronic hypertension: a real-world study

OBJECTIVE: This study aims to evaluate the real-world effectiveness of 100 mg aspirin in preventing superimposed preeclampsia (PE) in pregnant women with chronic hypertension (CHTN). STUDY DESIGN: This retrospective cohort study included pregnant women with CHTN who began prenatal care before 20 weeks of gestation and delivered a singleton at Nanjing Drum Tower Hospital, affiliated with Nanjing University Medical School. The deliveries occurred between January 1, 2018, and May 1, 2025. The primary exposure was 100 mg/day aspirin initiated between 12 and 20 weeks of gestation, and the primary outcome was the incidence of superimposed PE. Secondary outcomes included PE delivery before 34 weeks, PE delivery before 37 weeks, preterm birth, postpartum hemorrhage, gestational diabetes mellitus, small for gestational age (SGA), and a composite of adverse neonatal outcomes. Multivariable logistic regression and inverse probability of treatment weighting (IPTW) were used to adjust for confounding factors. RESULTS: During the study period, 367 women met the inclusion criteria, with 111 in the aspirin group and 256 in the control group. After IPTW adjustment, baseline characteristics were comparable between the two groups. The incidence of superimposed PE was 34.6% in the aspirin group and 37.7% in the control group, with no statistically significant difference (weighted OR = 0.87, 95% CI: 0.49-1.54; p >0.05). In secondary outcomes, the incidence of SGA was significantly lower in the aspirin group both before and after IPTW adjustment (p0.05). Additionally, subgroup analyses showed no significant heterogeneity in aspirin effect when stratified by aspirin-related factors (initiation timing, adherence, and concurrent calcium supplementation) or CHTN-related factors (timing of diagnosis, blood pressure levels before 20 weeks of gestation, and use of antihypertensive medication within three months prior to conception or before 20 weeks) (p >0.05). CONCLUSION: Our study suggests that initiating 100 mg/day of aspirin between 12 and 20 weeks of gestation does not significantly reduce superimposed PE in women with CHTN; however, it significantly reduces the risk of SGA. Subgroup analyses also indicated that even initiation before 16 weeks did not provide additional preventive effect against PE.