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Pregnancy BMI has little impact on children’s fatness

Genetics explains most of the association between maternal BMI and child fatness

Louise Prime

Friday, 27 January 2017

A woman’s body mass index (BMI) during pregnancy appears to have little long-term effect in itself on her children’s fatness in childhood and adolescence, UK-led research has found. Researchers behind the study,* published in PLOS Medicine, said this means that advising pregnant women to watch their weight with the aim of reducing population obesity may not be warranted. They suggested that interventions aimed at the whole population, such as proposals for excess tax on obesogenic foods, are potentially more likely to halt the obesity epidemic than focusing on overweight and obesity in pregnancy.

Previous studies have found that women with higher BMI during pregnancy tend to have larger babies, and it has been suggested that intrauterine exposure to higher levels of adiposity-related nutrients (such as glucose) results in permanent changes to offspring appetite control, neuroendocrine functioning, or energy metabolism, making them more likely to be fat later in life. But it had not been fully established whether or not these babies go into childhood and adolescence more overweight as a result of their mothers being overweight in pregnancy.

This group of researchers set out to investigate whether or not genetically elevated 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. To do so, they analysed body mass data and genetic information for 6,057 mother-child pairs from two prospective birth cohort studies, the Avon Longitudinal Study of Parents and Children (ALSPAC) and the Generation R study.

They found that there was little evidence to support the long-term impact of maternal BMI in pregnancy on the child’s risk of fatness in childhood and adolescence and that genetic transmission of BMI-associated variants explain most of the association between a mother’s BMI in pregnancy and her child’s fatness.

They concluded: “These findings suggest that public health interventions directed at all family members and at different stages of the life course are likely to be important and are potentially more likely to halt the obesity epidemic than a focus on maternal overweight and obesity status in pregnancy.”

But although they found no large effects of mothers being overweight or obese in pregnancy on their children’s risk of being fat in later life, they said we need further studies with relevant data to determine whether or not there might be smaller effects that their study was unable to detect.


* Richmond RC, Timpson NJ, Felix JF et al. Using genetic variation to explore the causal effect of maternal pregnancy adiposity on future offspring adiposity: a Mendelian randomisation study. PLoS Med 2017; 14(1): e1002221. DOI: 10.1371/journal.pmed.1002221.

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