The (low) impact of maternal BMI on childhood fatness

There is little evidence to support any long-term impact of maternal body mass index (BMI) in pregnancy on a child’s risk of fatness in childhood and adolescence, according to a study led by the University of Bristol.

Writing in the journal PLOS ONE, the authors cited previous research showing that a mother’s BMI during pregnancy is associated with greater birth size of her offspring. However, whether this association continues through childhood and is mediated by processes that occur during gestation — such as effects of circulating glucose and lipids levels — has until now been unclear.

“We wanted to investigate whether genetically elevated body mass index (BMI) of mothers in pregnancy was causally associated with higher levels of fatness in their offspring in childhood and adolescence, over and above the association expected given genetic transmission of BMI-associated variants,” the authors said.

The scientists sought to resolve this mystery by utilising the body mass and genetic information from 6057 mother–offspring pairs from two prospective birth cohort studies. In one cohort, the offspring’s BMI was measured around age six and in the other it was taken multiple times between ages seven and 18.

While the researchers found associations between maternal BMI before pregnancy and offspring BMI at all ages, these associations were largely explained by transmission of genes associated with fatness. And when a weighted genetic risk score was integrated into the analysis, the remaining association between pre-pregnancy BMI of a mother and her offspring’s childhood BMI was nearly null.

“Our findings provide little evidence to support the long-term impact of maternal BMI in pregnancy on the child’s risk of fatness in childhood and adolescence,” the authors said. “Rather, most of the association between a mother’s BMI in pregnancy and her child’s fatness is explained by genetic transmission of BMI-associated variants.”

The researchers concluded that public health interventions directed at all family members, and at different stages of the life course, are potentially more likely to halt the obesity epidemic than a focus on maternal overweight and obesity status in pregnancy.

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