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Exercising Moms-to-Be May Have Less-Chubby Babies

This could benefit newborns later in life, researcher suggests

WebMD News from HealthDay

By Amy Norton

HealthDay Reporter

WEDNESDAY, July 9, 2014 (HealthDay News) -- Babies born to mothers who exercise in late pregnancy may enter the world with a little less body fat, a new study finds.

Researchers said that could be a good thing, since extra fat at birth could continue into childhood and beyond. But the long-term health implications, if any, are not known yet.

"Body composition at birth is important," said Dr. Dana Dabelea, the senior researcher on the study and an associate professor at the University of Colorado School of Public Health.

"Two babies can be born at the same weight," Dabelea said, "but have different amounts of fat mass and lean mass."

Normally, a newborn's tiny body is mainly composed of the internal organs, bones and lean tissue -- with most of the "baby fat" coming later, Dabelea explained. So if exercise in late pregnancy does trim a bit of newborn fat, that could be a positive effect -- as long as it doesn't harm fetal growth and development, Dabelea said.

And that seemed to be true in this study, her team reports in the August issue of Obstetrics & Gynecology.

Looking at more than 800 mother-newborn pairs, the researchers found that when mothers exercised regularly in the third trimester, their babies were born with less fat, compared with newborns of less-active moms.

"But we didn't see any effect on lean mass," Dabelea said.

Experts already recommend that pregnant women get moderate exercise -- for their sake and their baby's. The American College of Obstetricians and Gynecologists says healthy pregnant women should aim for 30 minutes of moderate activity, such as brisk walking, most days of the week.

That's partly because exercise can reduce the amount of blood sugar that gets to the fetus, which cuts the risk of having a larger-than-normal baby, said Dr. Joseph Fernandez, an obstetrician/gynecologist with Scott & White Healthcare in Round Rock, Texas.

"There used to be some hearsay that women who exercise a lot during pregnancy will have a small baby," said Fernandez, who was not involved in the new study.

But he said these latest findings add to evidence that exercise benefits mothers-to-be and their babies.

The study included 826 Colorado women, average age 28, whose activity levels were tracked during pregnancy. Only 17 percent met the recommended guidelines on exercise. About 45 percent were overweight or obese.

In general, the researchers found, the one-quarter of women who were most active in late pregnancy tended to have less chubby babies than other mothers. Those active women were not running marathons -- most got a modest amount of exercise on most days of the week, Dabelea said.

The researchers did find that the most-active mothers had an increased risk of having a "small-for-gestational-age" newborn -- which means smaller than the norm for babies born during a given week of pregnancy.

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