Risk for early-onset neonatal bacterial sepsis among newborns increases with maternal body mass index (BMI), according to results from a nationwide, population-based, retrospective cohort study published in Clinical Infectious Diseases.

Data from 1,971,346 live singleton births in Sweden were collected between 1997 and 2016. Maternal BMI during pregnancy was assessed and infants were followed for their first 3 days to determine whether culture-confirmed early-onset neonatal bacterial sepsis was present.

Risk for early-onset neonatal bacterial sepsis was low (1.48 per 1000 live births) and was increased in preterm infants when compared with infants born full-term (15.52 vs 0.76 per 1000 live births). When compared with babies born to mothers with a normal BMI of 18.5 to 24.9 kg/m2, the early-onset neonatal bacterial sepsis infection risk was lowest for babies born to underweight women with a BMI of <18.5 kg/m2 (adjusted hazard ratio [aHR], 1.07; 95% CI, 0.83-1.40), and steadily increased with maternal weight (BMI 25.0-29.9 kg/m2: aHR, 1.19 [95% CI, 1.08-1.32]; BMI 30.0-34.9 kg/m2: aHR, 1.70 [95% CI, 1.49-1.94]; BMI 35.0-39.9 kg/m2: aHR, 2.11 [95% CI, 1.73-2.58]; BMI ≥40.0 kg/m2: aHR, 2.50 [95% CI, 1.86-3.38]).

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Maternal age, primiparity, height <165 cm, smoking during pregnancy, diabetes, hypertension, pre-eclampsia, infections, chorioamnionitis, and delivery before the year 2000 were all positively associated with early-onset neonatal bacterial sepsis risk. Emergency cesarean section delivery, pre-eclampsia, preterm delivery, and elective cesarean section delivery explained 47% of the association between BMI and early-onset neonatal bacterial sepsis.

The investigators observed a significant interaction between early pregnancy BMI and gestational age at delivery and infection risk in babies born full-term (P <.0001). When compared with normal-weight women, mothers with overweight and obesity grades 1, 2, and 3 had aHRs of 1.37 (95% CI, 1.20-1.56), 1.86 (95% CI, 1.55-2.22), 2.59 (95% CI, 1.99-3.37), and 2.82 (95% CI, 1.87-4.24), respectively.

When compared with siblings in a subcohort of 496,332 families, every 1 kg/m2 increase between pregnancies was associated with an average 8.3% increase in early-onset neonatal bacterial sepsis risk (95% CI, 1.7-15.3; P =.01).

Infection by group B Streptococcus, Staphylococcus aureus, other Staphylococci, and Escherichia coli increased in a dose-response fashion with maternal BMI. Escherichia coli infection risk, however, was 4.6 times higher in babies born to underweight mothers.

A potential limitation of this study was that maternal BMI and age were missing for 177,066 infants, which may have introduced selection bias; however, the investigators reported no change to their results after conducting multiple imputation analyses.

The study authors concluded that risk for early-onset neonatal bacterial sepsis infection among infants increased with maternal BMI and that awareness of these data may help to reduce infection rates among newborns.

Disclosure: Multiple study authors declared affiliations with industry. Please refer to the original reference for a full list of disclosures.


Villamor E, Norman M, Johansson S, Cnattingius S. Maternal obesity and risk of early-onset neonatal bacterial sepsis: nationwide cohort and sibling-controlled studies [published online June 17, 2020]. Clin Infect Dis. doi:10.1093/cid/ciaa783