Background There is growing evidence to support a link between maternal obesity in pregnancy and increased risk of adverse long-term outcomes for offspring. A number of studies have reported associations between maternal body mass index (BMI) and childhood infection. However, current evidence is limited, particularly in a UK context. The primary objective of this study is to explore associations between maternal BMI and childhood infection in primary care. The secondary objective is to investigate whether these relationships vary according to ethnicity and markers of socio-economic status (SES).

Methods Data from the Born in Bradford (BiB) longitudinal birth cohort study was linked to primary care data in Bradford, UK. All live, singleton births with maternal height and weight data available were included in this analysis. Women’s height was recorded at study enrolment and women’s weight was recorded during their booking appointment (at approximately 10 weeks’ gestation). The primary outcome was incidence of childhood infection, which was defined as either an infection-related visit to a general practitioner (GP) or a community prescription for an antibiotic. Multilevel negative binomial models were used to estimate rate ratios (RR) for overall infections and by infection type. Models were adjusted for socio-economic and pregnancy related factors. Interactions between maternal BMI, ethnicity and SES were added to models and evaluated using likelihood ratio tests.

Results 12,453 women were recruited, resulting in 13,858 live births. After excluding those with missing data, 11,208 women and their live, singleton babies were followed up from birth until study withdrawal or age 5 years. A total of 6,417 women (56%) were overweight or obese based on their BMI. 10,536 children (94%) had at least one infection. The most common infection types reported were skin and soft-tissue (38%) and upper respiratory tract infections (32.3%). Compared to those with a healthy BMI, children born to overweight or obese mothers had rate ratios of 1.07 (95% CI: 1.03–1.11) and 1.14 (95% CI: 1.09–1.18), respectively. After adjustment for potential confounders, being overweight in early pregnancy was no longer associated with childhood infection, however, being obese in early pregnancy remained significant, with RRs of 1.07 (95% CI: 1.03–1.13). This was most marked for lower respiratory tract infections. Results stratified by age, infection type, ethnicity and SES will be presented.

Conclusion Having a BMI outside of the healthy range during early pregnancy may be associated with an increased rate of infections throughout early childhood.