NEW YORK (Reuters Health) – Babies born to overweight or obese women have more fat and less muscle than infants born to normal-weight moms, according to one of the first studies to compare newborns' body composition to their mothers' pre-pregnancy body mass index (BMI).

Obesity is on the rise among pregnant women, while more and more North American and European infants weigh eight pounds 13 ounces or more at birth, Dr. David A. Fields of the University of Oklahoma Health Sciences Center in Oklahoma and colleagues Fields and his team note in their report in American Journal of Obstetrics & Gynecology. These unusually heavy infants are more likely to grow up to be obese.

Body weight alone, however, doesn't provide a clear picture of infant growth and health, the researchers add; both low and high birth weight have been tied to an increased risk of diabetes and other conditions in adulthood.

To better understand how prenatal growth might influence future health, Fields and his team used the PEA POD, a "body composition system" made by Concord, California-based Life Measurement Instruments, to measure the percentage of body fat, fat-free body mass, and total fat mass in 72 babies no older than 35 days. There was no difference in average birthweight between babies born to women with normal BMIs and those whose mothers were overweight or obese.

However, infants of the 39 overweight or obese moms had significantly higher percentages of body fat (13.6 vs. 12.5 percent), higher fat mass (448.3 grams vs. 414.1 grams), and lower fat-free mass (3,162.2 grams vs. 3,310.5 grams) than the babies born to the 33 normal-weight women, Fields and his team found.

Babies born to heavy mothers may face a greater risk of diabetes because they have less muscle mass, Fields noted in an interview. "That could be reason why these kids, probably many of them, will get diabetes, because muscle is your largest consumer of sugar," he said.