New research has found that children of obese parents are more likely to fail on developmental tests than children of normal weight parents.

Carried out by a team of researchers at the National Institutes of Health, the study looked at data collected from the Upstate KIDS study, a program which originally set out to look at the effect of fertility treatments on child development.

More than 5,000 women were included in the study between 2008 and 2010, enrolling around 4 months after giving birth and providing information on their own health and weight both before and after pregnancy, as well as the weight of their partners.

To assess the children's development, parents were asked to complete the Ages and Stages Questionnaire after carrying out activities with their children at 4 months of age, with children retested 6 more times up to age 3.

The results showed that when compared to children of normal weight mothers, children of obese mothers were nearly 70 percent more likely to have failed the test indicator on fine motor skill -- the ability to control movement of small muscles, for example in the fingers and hands -- by age 3.

Children of obese fathers were 75 percent more likely to fail the test's personal-social domain -- an indicator of social competence and how well children were able to relate to and interact with others by age 3, and those with two obese parents were nearly three times more likely to fail problem-solving ability tests by age 3.

Commenting on the importance of the findings, the study's first author, Edwina Yeung, Ph.D., said that, "The previous US studies in this area have focused on the mothers' pre- and post-pregnancy weight. Our study is one of the few that also includes information about fathers, and our results suggest that dad's weight also has significant influence on child development."

Although it is not known why having obese parents could affect a child's development, previous animal studies suggest that obesity during pregnancy could promote inflammation, affecting the fetal brain.

Less is known about how obese fathers could be affecting children's health but research suggests that obesity could affect the expression of genes in sperm.

More research needs to be carried out to investigate a potential link between parental obesity and delays in childhood development, however if confirmed the authors advise that physicians may need to take parents weight into account when testing young children's developmental skills.

Dr. Yeung and her coauthors also added that research indicates that as many as around 1 in 5 pregnant women in the United States is overweight or obese.

The results can be found published online in the journal Pediatrics.