Can weight gain in pregnancy cause childhood obesity?

The study used available data on 6,057 mother–child pairs from two prospective birth cohort studies, the Avon Longitudinal Study of Parents and Children (ALSPAC) in the former County of Avon, United Kingdom, and the Generation R study which took place in Rotterdam, the Netherlands. The studies were respectively conducted on women with an expected delivery date between April 1991 and December 1992, and between April 2002 and January 2006.

Building upon this data, a team of researchers led by the University of Bristol found that there was little evidence of a long-term impact of maternal BMI in pregnancy on the child’s risk of fatness, be it during childhood or adolescence. According to their work, genetic transmission of BMI-associated variants would actually explain most of the association between mother and child fatness.

To get to this conclusion, the team used an intergenerational Mendelian randomisation (MR) method where maternal genetic variants were used as instrumental variables (IVs) for environmentally modifiable intrauterine exposures, such as exposure to greater maternal adiposity. The researchers believed that this approach could be useful for providing insights into the causal effect of these exposures on later offspring outcomes.

‘Given our results, together with those from sibling comparison and negative control studies, it seems unlikely that subtle incremental differences in maternal pre- or early-pregnancy BMI play a key role in initiating or perpetuating the obesity epidemic,’ the study reads. Some negative control and sibling comparisons suggested weak positive effects, but these effects were eventually discarded. ‘Those studies are smaller than the ones finding null effects and have not explored associations into adulthood,’ the team explains.

These findings pushed the authors of the study, which was published in PLOS Medicine, to draw two main conclusions. The first is that ‘overreliance on interventions in pregnancy to reduce population obesity may not be warranted’. The second, that ‘consensus statements, which direct public health interventions to all family members and at different stages of the life course, and not just intrauterine or early life, are likely to be important.’

OBESITYDEVELOP, which started in November 2015 and is due for completion in 2020, will keep looking into adverse effects of overweight in pregnancy across generations for the years to come. In total, data from up to 100 000 participants will be analysed to determine the impact of pregnancy BMI on weight and cardiometabolic health at fetal development, infancy to adulthood and on to the next generation.

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