Maternal obesity linked to children's heightened risk of infection-related hospitalizations

Children born to mothers who are very obese with a BMI of 35 or higher are at heightened risk of being admitted to hospital for an infection, finds a long term study published in the open access journal BMJ Medicine.

The findings highlight the importance of maintaining a healthy body weight before and after the pregnancy, say the researchers.

On current trends, the global prevalence of maternal obesity is projected to reach nearly 1 in 4 (23%) by 2030, point out the researchers. This is of particular concern, given that obesity is characterized by a state of chronic inflammation, which increases the risk of a disordered immune system response, changes in gene expression, and unfavourble changes to the gut microbiome alterations, all of which can influence the long term health of the developing fetus, they add.

Previously published studies on whether maternal weight is associated with childhood infection have failed to reach consensus, and it's unclear if various potentially modifiable factors, such as breastfeeding, method of delivery, and pregnancy weight gain, might influence outcomes, say the researchers.

To find out, 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.

Women (9037) 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. 

Some 4196 (45%) women were of Pakistani, and 3742 (40%) of white British, ethnicity. And 37% of the entire sample lived in the most socioeconomically deprived areas of the UK. 

Their children's (9540) health-specifically, number of admissions to hospital for an infection and number of infections within their first 5 years-was tracked from birth until the age of 15, they withdrew from the study, or died, whichever came first by October 2022.

Infections were categorised as: upper respiratory tract; lower respiratory tract; skin and soft tissue; genitourinary; gastrointestinal; invasive bacterial; and multisystem viral.

The authors looked at whether particular factors might affect the association between maternal BMI and childhood infection. These included: breastfeeding for 6 or more weeks after birth; caesarean (C) section delivery; preterm birth under 37 weeks; excessive weekly average weight gain and excessive total weight gain while pregnant; and child obesity.

The mums-to-be were weighed at the first antenatal (booking) appointment; again between 26-28 weeks of pregnancy, together with height; and during a routine third trimester appointment. About 30% of the women were overweight and 26% were obese, which included 10% who were grades 2-3 obese (BMI of 35 or above), based on first trimester BMI.

In all, there were 5009 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 5-15 year olds. 

Crude admission rates rose in tandem with BMI: 39.7 admissions/1000 person years among children whose mothers were a healthy weight compared with 60.7/1000 person years among those whose mothers were obese (grades 2-3).

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 1 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. And they were 53% more likely to do so between the ages of 5 and 15.

The observed associations were slightly stronger in boys than in girls, and in Pakistani women than in white British women. Respiratory, gastrointestinal, and multisystem viral infections accounted for most of the excess hospital admissions.

Of the potentially modifiable factors assessed, preterm birth accounted for a modest proportion of the association (7%) between obesity grades 2-3 and childhood infections during the first five years. 

But C-section birth accounted for 21% and child obesity at age 4-5 accounted for 26%, suggesting these might be potentially modifiable risk factors, suggest the researchers. Breastfeeding for 6 or more weeks and excessive pregnancy weight gain (both average weekly and total) weren't significantly associated.

This is an observational study, and as such, can't establish cause and effect. The researchers also acknowledge that their study relied on data from only one hospital and substantial amounts of information on breastfeeding and child BMI were missing. Nor were they able to factor in environmental and lifestyle factors.

But they nevertheless conclude: "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."