Maternal obesity shapes associations between preeclampsia and birthweight in pregnancies exposed to low-dose aspirin.

Introduction: Preeclampsia is a major cause of maternal and perinatal morbidity and is associated with substantial variability in gestational duration and fetal growth. Low-dose aspirin (LDA) is widely used in pregnancies at increased risk, although perinatal outcomes may vary across clinically defined maternal subgroups. Methods: We conducted a Results: Preeclampsia was associated with lower birthweight in both sexes (MD = -747.6 g, p < 0.0001 in females; MD = -867.7 g, p = 0.0127 in males), with a substantial proportion of these differences captured by shorter gestational duration in the mediation model (MD = -2.81 weeks, p < 0.0001 in females; MD = -3.16 weeks, p = 0.0017 in males). Within LDA-exposed pregnancies, no statistically significant differences in birthweight or gestational age relative to the reference profile were observed across obesity strata in male newborns. In female newborns, maternal obesity was associated with lower birthweight (MD = -1002.9 g, p = 0.0003) and shorter gestational age (MD = -2.60 weeks, p = 0.0497), including a non-mediated component estimated within the modeling framework (MD = -506.6 g, p = 0.0043), although estimates in the smallest profiles should be interpreted as exploratory. Discussion: These findings describe heterogeneity in the associations linking preeclampsia, gestational duration, and fetal growth across maternal obesity and LDA exposure strata. Within this observational framework, the findings support a more contextualized interpretation of perinatal variability across risk-defined clinical profiles.