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If you're pregnant, you might want to pay close attention to your body mass index.

New research has suggested that pregnant women who are overweight or obese can encounter a host of health complications and affect how their children initially grow and develop.

The study was published in the Journal of Pediatrics.

A team of researchers studied 97 mothers. None were diabetic and 38 were overweight or obese. They compared the weight and height of babies born to overweight and obese mothers with those born to normal-weight mothers.

They found that babies of overweight/obese mothers gained less weight and grew less in length than babies of normal-weight women from just after birth to three months. The overweight/obese mother babies also gained less fat mass than those born to normal-weight mothers. Fat mass in infants is widely considered to be crucial to brain growth and development.

Katie Larson Ode, assistant clinical professor in pediatric endocrinology and diabetes at the University of Iowa said that children from overweight/obese mothers are not growing normally.

 "If what we have found is true, it implies that the obesity epidemic is harming children while they are still in utero and increases the importance of addressing the risk of obesity before females enter the child-bearing years, where the negative effects can affect the next generation," Larson Ode said.

A 2010 study published in the journal of the American Medical Association said that 60 percent of women in the United States who are of childbearing age are overweight or obese.

Past studies have shown that children of overweight or obese mothers generally catch up to their normal-weight-mother peers at some point, but have a higher risk of continuing to rapidly gain weight in adolescence and becoming fat themselves, triggering health problems throughout their lifetimes.

Larson Ode said people should not panic based on the results of the study.

"Pediatricians see a lack of (initial) growth, and they assume the child is not getting enough nutrition. But we believe the baby is in fact getting plenty," she said.

The researchers think there are two reasons why babies of overweight or obese women lag initially in their physical development.

The first deals with inflammation where fat cells that normally help suppress a person's immune system flare up when an adult is overweight.  

"These (fat tissue-derived) hormones and inflammatory factors tend to have appetite/satiety regulating effects early on, and may exert their negative effects on growth both during gestation and through passage into the breast milk during postnatal development as well," Ellen Demerath, senior author on the paper, said.

The second cause has to do with how babies grow in the womb. One is through free fatty acids delivered by the mother via a growth hormone called IGF-1. The other is through a growth hormone secreted by the pituitary gland in the baby's brain. The researchers think the cosseted baby is getting so many free fatty acid-derived growth hormones from its overweight mother that the other growth generator-the pituitary gland-slows its production.

The researchers found babies of overweight/obese mothers gained 11 ounces less than those born to normal-weight mothers from two weeks to three months. They also put on 0.3 ounces less fat mass and grew nearly a half-inch less.

However, researchers said the sample size was small and the findings need to be confirmed with a larger population, as well as the possible reasons.