Women who gain excessive weight during pregnancy are at higher risk of having overweight or obese children, according to a study published in the journal PLOS Medicine.

Researchers from Boston Children’s Hospital, Massachusetts, conducted a population-based cohort study of 42,133 women who had more than one singleton pregnancy and their 91,045 children.

The study involved matching records of all live births in Arkansas with state-mandated data on childhood body mass index (BMI) and height from public schools between 2003 and 2011.

The researchers wanted to determine whether childhood obesity is due to conditions during pregnancy, which can influence birthweight, or whether other shared mother and child factors, such as genes and diet, play a part.

The results of the study showed that on average, mothers gained around 14 kg in each pregnancy.

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Researchers say that for every kilogram of weight a mother gains during pregnancy, at age 12 their child’s BMI will increase by 0.02 kg/m2.

Using a within-family design (testing associations within each family), the researchers found that for every kilogram of weight a mother gained during pregnancy, their child’s BMI would increase by 0.02 kg/m2 (8%) by age 12.

When the researchers adjusted the results for differences in birthweight, this increase in weight still remained significant.

Overall, variations in pregnancy weight gain accounted for a 0.43 kg/m2 difference in childhood BMI. By comparison, there has been an estimated 2 kg/m2 increase in the average BMI of children in the US since the 1970s.

The researchers note that although it would have been useful to include data of the mothers’ pre-pregnancy BMI in this study, this would have differentiated the results further since women with higher BMI tend to gain less weight during pregnancy.

“The main limitation of this study is lack of prepregnancy body weight and BMI for the mothers. Therefore, we can’t translate these findings to specific pregnancy weight gain recommendations for individuals,” Dr. David Ludwig, of the Boston Children’s Hospital and study author, told Medical News Today.

“Moreover, we know that inadequate pregnancy weight gain can also cause major immediate and long-term complications for the offspring. For all but the most obese mothers, some weight gain is necessary to ensure good nutrition to the developing fetus.”

Because childhood body weight predicts adult body weight, the study authors say their findings suggest that overnutrition in pregnancy may program the fetus for an increased lifetime risk for obesity, although the magnitude of this effect may be small.

Dr. Ludwig told Medical News Today:

These findings suggest that pregnancy weight gain could program the offspring to an increased long-term risk for obesity, independent of genes and environment. In other words, obesity could propagate across generations, unless something is done to break this vicious cycle.

Though relatively small on an individual basis, the effects we found could explain several hundred thousand cases of childhood obesity globally each year.”

Dr. Ludwig notes that more research is needed to further examine the link between pregnancy weight gain and childhood obesity.

“Additional research is needed to examine the physiological mechanisms through which overnutrition during pregnancy affects the long-term health of the offspring,” says Dr. Ludwig. “Also, public health measures to avoid excessive, not just inadequate, pregnancy weight gain are warranted.”

Earlier this year, Medical News Today reported on a study suggesting that mothers who smoke during pregnancy are at higher risk of their daughter becoming obese or developing gestational diabetes.