Babies of heavy mothers have more fat, less muscle

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 4,000 grams (8 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.

"It's been very, very difficult to measure the body fat in the baby," Fields noted. Previously, doing so required using several different machines and took hours. The PEA POD can gauge body composition in five minutes, according to Life Measurement Instruments' Web site.

The machine is expensive, Fields noted, estimating that just 15 are in use worldwide. Nevertheless, he predicted that more and more hospitals will begin using them.

Gauging babies' body composition at birth could provide a clearer picture of their health than weight alone, Fields added, but then the question remains as to what should be done if babies are found to have a high percentage of body fat. One possibility, Fields said, would be to encourage their mothers to breastfeed. His own research has demonstrated that formula-fed babies tend to be fatter.

SOURCE: American Journal of Obstetrics & Gynecology, April 2008.