Aspirin prophylaxis for superimposed preeclampsia in women with chronic hypertension: a retrospective cohort study.

OBJECTIVE: Chronic hypertension (CHT) is a major risk factor for superimposed preeclampsia, but the effectiveness of aspirin prophylaxis in women with CHT remains uncertain, particularly in Asian populations. We evaluated the association of aspirin use with superimposed preeclampsia and related maternal and perinatal outcomes in Chinese women with CHT. METHODS: We conducted a retrospective cohort study of 504 singleton pregnancies with CHT initiating prenatal care at 8-20 weeks of gestation across two coordinated tertiary hospitals (2013-2025). Participants were stratified by aspirin (n = 307) or no aspirin (n = 197). Multivariable logistic regression adjusted for confounders, and dose effects were explored. RESULTS: Compared with no aspirin exposure, aspirin use was associated with lower adjusted odds of superimposed preeclampsia (adjusted odds ratio [aOR], 0.183 [95% CI, 0.119-0.280]), early-onset preeclampsia before 34 weeks (aOR, 0.092 [95% CI, 0.050-0.168]), and preterm preeclampsia before 37 weeks (aOR, 0.142 [95% CI, 0.087-0.231]; all P < 0.001). Aspirin use was also associated with lower risks of preterm birth, placental abruption, thrombocytopenia, small for gestational age, neonatal asphyxia, neonatal intensive care unit admission, respiratory support, hypoxic-ischemic encephalopathy, stillbirth, and perinatal death. In exploratory within-group analyses, higher aspirin dose was associated with lower frequencies of superimposed preeclampsia and several adverse maternal and neonatal outcomes. Aspirin use was not associated with higher rates of cesarean delivery or postpartum hemorrhage. CONCLUSION: In Chinese women with CHT, early-to-mid pregnancy aspirin use significantly reduces superimposed preeclampsia odds and adverse perinatal outcomes without increasing bleeding risks. The potential dose-response pattern requires prospective validation.