We already know that children who are exposed to antibiotics at an early age may be associated with obesity in their early years. However, this study is the first to show that offspring of pregnant mothers who take antibiotics during the second or third trimester have an 86% increased risk of becoming obese by age 7 compared to those mothers not taking antibiotics. This was according to an article published out of Columbia University in the November 2014 issue of the International Journal of Obesity. They also found that 16% of pregnant women take antibiotics.
In a second study showed that having a C-section increased the odds of obesity by age 7 in 46%. Go figure! They suspected that somehow this was related to the microbiome. I suppose it is possible, but more studies are needed to prove this. Mechanisms of how this might work are discussed.