A Child's BMI Is Mostly Influenced by Genetics, Rather Than Pregnancy Weight

A child’s weight is mostly influenced by genetics rather than the weight of their mother during pregnancy, researchers have found.

In the largest study of its kind, childhood body mass index (BMI) data from 86,000 children was examined in a study between The University of Queensland, University of Bristol and Norwegian Institute of Public Health.

Professor David Evans from UQ’s Institute for Molecular Bioscience, who co-led the study, said higher parental BMI is consistently associated with higher childhood BMI, but until now it has been difficult to determine how much is due to genetics or intrauterine effects.

“The world and western nations in particular are gripped by an obesity pandemic,’’ Professor Evans said.

“We were interested in examining whether obesity in mothers during pregnancy might also increase the risk of obesity in their children through intrauterine mechanisms.

“Our research suggests that whilst obesity during pregnancy has short-term effects on a child’s birthweight, the effect is not long term.

“The major reason for the strong link between a mother and her child’s weight is because they share half the same genes.’’

Using data from the Norwegian Mother, Father and Child Cohort Study, researchers analysed birth weight and BMI of children from 6 months to 8 years of age, as well as appetite-related eating behaviours at 8 years old.

The researchers looked at twin, sibling, and half-sibling relationships across multiple generations to quantify how much of the parent-child BMI association could be attributed to genetics.

Professor Evans said the results do not diminish the importance of maternal health in pregnancy, as research shows maternal obesity increases the risk of adverse perinatal outcomes for both mother and child.

“Obesity is a major risk factor for all sorts of chronic diseases including type 2 diabetes, heart disease and various cancers,’’ Professor Evans said.

“It’s important we take major steps to reduce the prevalence of overweight and obesity in the population.

“But these results should reduce the stigma that mothers who are overweight during pregnancy are somehow responsible for their offspring being overweight.’’

Dr Tom Bond from University of Bristol said obesity runs in families, but it has been difficult to work out why this is.

“Our results suggest that the link between a mother's or father's BMI and their children's BMI up to age 8 is mostly due to inherited genes,’’ he said.

“Expectant parents should be encouraged to maintain a healthy weight, but this may not be enough to ensure that their children also have a healthy weight."

Reference: Bond TA, McAdams TA, Warrington NM, et al. Parental body mass index and offspring childhood body size and eating behaviour: A structural equation modelling analysis in the Norwegian Mother, Father and Child Cohort Study. PLOS Med. 2026;23(6):e1005094. doi: 10.1371/journal.pmed.1005094

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