Maternal obesity linked to increased risk of infection-related hospital admissions in children, study finds

Key Takeaways:

• Children born to people with obesity (BMI ≥35) face a significantly increased risk of hospital admission for infections up to age 15.
• The risk is most pronounced during infancy and again between ages 5 and 15, with respiratory, gastrointestinal, and viral infections driving most admissions.
• Caesarean delivery and child obesity in early years appear to partly explain the association, suggesting potential areas for public health intervention.

Introduction

A long-term UK study published in BMJ Medicine has found that children born to women with obesity—specifically those with a body mass index (BMI) of 35 or above—are at an elevated risk of hospitalisation due to infections. The study, based on nearly 10,000 births in Bradford, England, highlights how maternal health before and during pregnancy can have long-lasting implications for child health, particularly regarding immune-related outcomes.

Global and Biological Context

Researchers emphasise that maternal obesity is a growing global health issue, with estimates suggesting it could affect nearly 1 in 4 pregnancies worldwide by 2030. Obesity is marked by chronic low-grade inflammation, which is associated with a range of biological changes—disruption of immune function, alterations in gene expression, and changes to the gut microbiome—all of which may influence foetal development and subsequent childhood health.

While past studies have investigated the potential link between maternal obesity and childhood infections, findings have been inconsistent. Furthermore, it has remained unclear whether modifiable factors such as breastfeeding, method of delivery, and pregnancy-related weight gain might influence this relationship.

Study Design and Population

To explore these questions, researchers analysed data from the Born in Bradford study, a prospective birth cohort that investigates how social, environmental, and genetic factors affect maternal and child health over time.

The analysis included 9,037 women who gave birth to a live infant at Bradford Royal Infirmary between March 2007 and December 2010 and for whom both height and weight data were available. Of these participants:

• 45% were of Pakistani origin,
• 40% were white British, and
• 37% lived in the most socioeconomically deprived areas of the UK.

In total, 9,540 children were followed for health outcomes—specifically hospital admissions for infections—from birth until October 2022, or until the child either withdrew from the study, died, or turned 15.

Maternal BMI and Measurement

Maternal BMI was assessed at multiple time points:

• At the first antenatal (booking) appointment,
• Again between 26 and 28 weeks’ gestation, and
• During a routine third-trimester appointment.

Approximately 30% of the women were classified as overweight, and 26% were living with obesity—10% of whom had obesity grades 2 or 3 (BMI ≥35) in the first trimester.

Infection Categories and Hospital Admissions

Childhood infections were classified into several categories:

• Upper respiratory tract,
• Lower respiratory tract,
• Skin and soft tissue,
• Genitourinary,
• Gastrointestinal,
• Invasive bacterial, and
• Multisystem viral infections.

Over the follow-up period, 5,009 infection-related hospital admissions were recorded. Around 30% of the children were hospitalised for an infection at least once:

• 19% had one admission,
• 6% had two,
• 4% had three or more.

Admission rates were highest during infancy—134.6 admissions per 1,000 person-years—which declined to 19.9 per 1,000 person-years in children aged 5 to 15.

Maternal BMI and Infection Risk

There was a clear gradient in infection risk according to maternal BMI:

• Children of mothers with a healthy BMI had an admission rate of 39.7 per 1,000 person-years.
• This increased to 60.7 per 1,000 person-years among children whose mothers had obesity grades 2-3.

After adjusting for potential confounders (maternal age, ethnicity, and area deprivation), the risk remained significantly higher in children born to people with obesity grades 2-3:

• These children were 41% more likely to be admitted for an infection under age 1.
• They were 53% more likely to be admitted between ages 5 and 15.

The association appeared stronger in boys than girls and among children of Pakistani mothers compared to those of white British mothers. Respiratory, gastrointestinal, and viral infections accounted for the majority of excess hospital admissions.

Modifiable Risk Factors

The researchers explored whether certain modifiable factors might influence this association:

• Preterm birth accounted for 7% of the link between maternal obesity and infection risk.
• Caesarean section delivery accounted for 21%.
• Child obesity at ages 4–5 contributed to 26%.

Interestingly, breastfeeding for six or more weeks and excessive pregnancy weight gain (both average weekly and total) were not significantly associated with infection risk in this study.

Limitations and Interpretation

As an observational study, the findings cannot establish causality. Several limitations were noted:

• Data came from a single hospital in Bradford, limiting generalisability.
• Missing data for breastfeeding duration and child BMI weakened the completeness of some analyses.
• Environmental and lifestyle factors—such as household crowding or exposure to smoking—were not included.

Despite these limitations, the authors argue that the findings underscore a broader public health concern. They write:

“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 obesity grades 2–3, the potential effect on a large number of children globally is substantial.”