Maternal Obesity and Risk of Early-onset Neonatal Bacterial Sepsis: Nationwide Cohort and Sibling-controlled Studies

Background Maternal overweight and obesity are related to risks of pregnancy and delivery complications that, in turn, are associated with newborn infections. We examined the associations between early pregnancy body mass index (BMI; kg/m2) and risk of early-onset neonatal bacterial sepsis (EOS). Methods We conducted a nationwide population-based retrospective cohort study of 1 971 346 live singleton infants born in Sweden between 1997 and 2016. Outcome was a culture-confirmed EOS diagnosis. We estimated hazard ratios (HR) of EOS according to BMI using proportional hazard models, and identified potential mediators. Among term infants, we conducted sibling-controlled analyses. Results EOS risk per 1000 live births was 1.48; 0.76 in term and 15.52 in preterm infants. Compared with infants of normal-weight mothers (BMI, 18.5–24.9), the adjusted HR (95% confidence interval [CI]) of EOS for BMI categories <18.5, 25.0–29.9, 30.0–34.9, 35.0–39.9, and ≥40.0 were, respectively, 1.07 (.83–1.40), 1.19 (1.08–1.32), 1.70 (1.49–1.94), 2.11 (1.73–2.58), and 2.50 (1.86–3.38). Maternal overweight and obesity increased the risk of EOS by group B Streptococcus, Staphylococcus aureus, and Escherichia coli. Half of the association was mediated through preeclampsia, cesarean section delivery, and preterm delivery. A dose-response association was consistently apparent in term infants only. In sibling-controlled analyses, every kilogram per meter squared interpregnancy BMI change was associated with a mean 8.3% increase in EOS risk (95% CI, 1.7%–15.3%; P = .01). Conclusions Risk of EOS increases with maternal overweight and obesity severity, particularly in term infants.