Maternal obesity is associated with increased risk of hospital admission for infection in children

Published on Tuesday, 03 June 2025 Post

A new study by researchers at Oxford Population Health's National Perinatal Epidemiology Unit has found that children born to mothers with a body mass index (BMI) of 35 or above may have an increased risk of being admitted to hospital for an infection. The study is published in BMJ Medicine.

Maternal obesity is projected to reach nearly one in four mothers worldwide by 2030. This is of particular concern because obesity is characterised by a state of chronic inflammation, which increases the risk of a disordered immune system response, changes in gene expression, and unfavourable changes to the gut microbiome alterations, all of which can influence the long-term health of a developing fetus.

Previous studies on whether maternal BMI is associated with childhood infection have had varied results. It has been unclear whether various potentially modifiable factors, such as breastfeeding, method of delivery, and pregnancy weight gain, might influence outcomes.

The researchers drew on participants in the Born in Bradford study, which has been looking at the potential impact of social, environmental, and genetic factors on short- and long-term mother and child health outcomes. They looked at data from 9,037 women who had given birth to a living child at the Bradford Royal Infirmary between March 2007 and December 2010, and for whom information on their height and weight was available, were included in the analysis. The health of the 9,540 children, specifically the number of admissions to hospital for an infection was tracked until the age of 15, they withdrew from the study, or died, whichever came first by October 2022.

They also took into account other factors that may explain the findings, including assessing potentially modifiable factors: breastfeeding for six or more weeks after birth; caesarean (C) section delivery; preterm birth under 37 weeks; excessive weekly average weight gain during pregnancy; excessive total weight gain while pregnant; and child obesity. The women were weighed at the first antenatal (booking) appointment, again between 26-28 weeks of pregnancy, and during a routine third trimester appointment.

Key findings:

• 4,196 (45%) women were of Pakistani and 3,742 (40%) were of white British ethnicity. More than a third (37%) of the entire sample lived in the most socioeconomically deprived areas of the UK. 30% of the women were overweight and 26% were obese (including 10% grade 2-3 obese), based on first trimester BMI;
• In all, there were 5,009 hospital admissions for infection between birth and the age of 15. About 30% of the children were admitted to hospital for infection at least once up to the age of 15. 19% were admitted once, 6% twice, and 4% 3 or more times;
• The highest admission rates were among infants under a year of age (134.6 admissions/1000 person years, which fell to 19.9/1000 person years among five- to 15-year-olds[LP5] ;
• After adjusting for potentially influential factors, maternal BMI was positively associated with rates of hospital admission for infection across all ages, but the results were statistically significant only for children whose mothers were the heaviest (obesity grades 2-3);
• These children were 41% more likely to be admitted to hospital for an infection when they were under a year old after accounting for potentially influential factors, such as mother's age, ethnicity, and area deprivation level, compared with those with mothers of a healthy weight. They were 53% more likely to be admitted to hospital between the ages of five and 15;
• In terms of potentially modifiable factors assessed, preterm birth accounted for a modest proportion of the association (7%) between mothers with the highest levels of obesity and childhood infections up to age five. However, C-section birth accounted for 21% and child obesity at ages four to five accounted for 26% of cases;
• Breastfeeding for six or more weeks and excessive pregnancy weight gain (both average weekly and total) weren't significantly associated with an increased risk of childhood infection.

Victoria Coathup, Researcher in Epidemiology and Statistics and first author of the study, said:

Our findings highlight the importance of maintaining a healthy body weight before and after pregnancy. Our study is observational so is not able to establish whether obesity directly causes childhood infections. However, the findings of our study highlight the need for public health campaigns and additional support for healthcare professionals to help women of reproductive age achieve and maintain a healthy body weight. Although the results indicated a modest effect of maternal obesity, and only in those with the highest levels of obesity, the potential effect on a large number of children globally is substantial.