Late-Pregnancy Exercise May Trim Newborns' Baby Fat

By Anne Harding

July 16, 2014

NEW YORK (Reuters Health) - Babies born to women with the highest levels of physical activity in late pregnancy have less body fat than infants whose mothers were the least active in their third trimester, new findings show.

"Exercise during pregnancy according to our data seems to be a good thing because it reduces neonatal adiposity without affecting newborn fat-free mass," Dr. Dana Dabelea of the Colorado School of Public Health at the University of Colorado at Denver told Reuters Health.

"Although we don't know exactly how body composition at birth is related to future risk of obesity, there is increasing evidence that adiposity early in life tracks over time and is associated with a higher risk of childhood obesity and adult obesity," she said.

American College of Obstetricians and Gynecologists guidelines say that pregnant women should log 30 minutes of moderate physical activity on most days of the week, Dr. Dabelea and her team note in their report, published online July 7 in Obstetrics & Gynecology.

There is evidence that exercise in pregnancy improves blood flow to the fetus, they add, and it may also help prevent macrosomia.

To investigate the effect of maternal exercise on fetal body composition, the researchers looked at 826 mother-child pairs. Women completed the Pregnancy Physical Activity Questionnaire during early, mid- and late pregnancy. The investigators used air displacement plethysmography to assess infants' body composition within 72 hours after birth.

Neonates' mean fat mass was 292.9 grams, while their fat-free mass was 2,849.8 grams. There were 107 babies who were small for gestational age (SGA), and 30 who were large for gestational age.

Infants born to the mothers in the top quartile based on energy expenditure had 41.1 grams less fat mass than babies born to mothers in the bottom quartile of energy expenditure.

There was no association between energy expenditure and fat-free mass or birth weight. However, babies born to the most active mothers were three times more likely to be SGA than those whose mothers were the least active.

Overall, 17.4% of the mothers met ACOG's physical activity guidelines throughout their pregnancy. There was no difference in neonatal outcomes between babies born to the mothers who met the guidelines and those whose mothers did not.

Dr. Dabelea noted that the increased risk of SGA among babies born to the most active mothers was likely related to their lower fat mass, and not due to growth restriction, given that their fat-free mass was the same.

The researcher said she and her colleagues are now looking at other factors including smoking, diet, gestational weight gain and maternal metabolic markers to see how they may affect babies' body composition, and would like to follow the current cohort until they reach adolescence.

Dr. Lana Mudd, an assistant professor of kinesiology at Michigan State University in East Lansing who studies physical activity during pregnancy, welcomed the new work.

"This is a really important study, and a very interesting finding, especially as regards to the body composition result," Dr. Mudd told Reuters Health.

The study included 16.7% non-Hispanic black participants, 23.7% Hispanic women, 53.4% non-Hispanic whites, and 6.2% other eccentricities. This is a more diverse sample than has been included in other similar studies, Dr. Mudd noted.

"To have a more diverse sample and see these results is really encouraging," she said. Another unique aspect of the study, Dr. Mudd added, was that it looked at physical activity for different time points during pregnancy.

"They really saw that the action was in the late pregnancy physical activity, which isn't totally surprising," she said. "Some smaller studies that were done on very selected samples of women have indicated that the third trimester or later in pregnancy might be a more important time frame for having an effect. That could be for a lot of reasons, but mainly the majority of fetal growth is occurring later in pregnancy."

Dr. Mudd agreed that the increase in risk of SGA with more physical activity was likely due to the reduction in fat mass, and not a cause for concern.

"This provides further evidence of positive health benefits of physical activity during pregnancy and provides greater rationale for promoting physical activity during pregnancy," she concluded.

SOURCE: http://bit.ly/1zEly7e

Obstet Gynecol 2014.

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