Expectant Mom's Exercise Keeps Newborn's Birth Weight Down

May lower baby's risk of obesity later in life, research suggests

MONDAY, April 5 (HealthDay News) -- Regular moderate-intensity exercise during pregnancy reduces an infant's birth weight, which may lower the child's risk of obesity later in life, researchers say.

In a new study, 84 first-time pregnant women were randomly assigned to exercise or control groups, with those in the exercise group participating in a weekly maximum of five 40-minute sessions on a stationary cycle. They did this program until at least 36 weeks into their pregnancy.

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Babies born to mothers in the exercise group were an average of 143 grams lighter than infants born to mothers in the control group, and also had a lower body-mass index (a measurement that takes into account height and weight), the researchers found.

The exercise training had no effect on the mothers' body weight or body-mass index during late pregnancy, and had no effect on insulin resistance from the start of the study to late gestation, according to the report published online in the Journal of Clinical Endocrinology & Metabolism.

"Our findings show that regular aerobic exercise alters the maternal environment in some way that has an impact on nutrient stimulation of fetal growth, resulting in a reduction in offspring birth weight," study co-author Dr. Paul Hofman, of the University of Auckland in New Zealand, said in an Endocrine Society news release. "Given that large birth size is associated with an increased risk of obesity, a modest reduction in birth weight may have long-term health benefits for offspring by lowering this risk in later life."

Hofman added that the "physiological response to pregnancy appears to supersede the chronic improvements in insulin sensitivity previously described in response to exercise training in non-pregnant individuals. This may be an important finding for athletes who want to continue regular training during their pregnancy as it suggests that training will not have a major adverse impact on insulin resistance."

More information

The Nemours Foundation has more about exercising during pregnancy.

-- Robert Preidt