There is no benefit for children's bone mass if women gain weight during pregnancy, says a new study.

And this applies to both normal and overweight women prior to pregnancy, says Teresa Monjardino, lead author from the Universidade do Porto in Portugal. Weight management strategies during pregnancy reduce child cardiometabolic risk such as diabetes and heart disease. However, because maternal weight has an overall positive correlation with a child's bone mass, pregnancy weight management could adversely affect child bone health, said the researchers. 

The study, published in the Journal of Bone and Mineral Research, showed that in under and normal weight mothers, weight gain during pregnancy was associated with slightly increased bone mass at 7 years of age in children. On the other hand, in the case of overweight or obese mothers, no beneficial effect of weight gain on bone mass was observed.

"Until recently, it was a widely held scientific belief that any weight gain from the mother during pregnancy would have a beneficial effect on children's bone mass," said Monjardino.  "Our study results corroborate that there is no benefit in gaining weight above the US Institute of Medicine recommendations for pregnancy weight gain for children's bone mass, in both normal and overweight women prior to pregnancy," added Monjardino. The team analysed prospective data from 2,167 mother-child pairs.