Being physically active while pregnant may help women gain a little bit less weight, according to a new review of recent research.
Pooling the results of 12 studies, researchers in Munich, Germany, found that women who exercised while pregnant gained an average of 1.3 fewer pounds than women who didn't.
That alone is probably not much of an incentive for women who are considering exercising while pregnant, but there are other reasons to do it, said Dr. Michael Kramer of McGill University in Montreal who reviewed the findings for Reuters Health.
Research shows that exercise can have positive effects on mood and insulin sensitivity in people overall, and appears to have no negative effects on women during pregnancy, noted Kramer, who is also scientific director of the Institute of Human Development, Child and Youth Health at the Canadian Institutes of Health Research.
Exercise can also help women maintain their pre-pregnancy conditioning.
"Women who have been physically active can continue, and women who haven't can start," Kramer said. "But they shouldn't expect major outcomes for them or their baby."
Women who gain too much weight in pregnancy are at risk of a number of problems, including diabetes, high blood pressure, and labor complications.
A recent study also found that women who gained more weight during pregnancy gave birth to heavier babies, who in turn are themselves more likely to become obese adults. They also may be more prone to cancer, allergies, and asthma.
To investigate if exercise programs help women avoid the trouble that comes from too much weight gain, Ina Streuling of the Ludwig-Maximilians University of Munich and colleagues reviewed data from 12 studies that looked at the effect of an exercise intervention on women during pregnancy.
Collectively, the studies compared more than 1,000 women, some of whom were randomly assigned to follow an exercise program.
The programs encouraged women to exercise approximately three times per week, up to one hour of aerobics, running, biking or muscle strengthening, starting in the first or second trimester.
The studies did not uniformly show that exercise was associated with less weight gain in pregnancy, but overall, the data trend in that direction, said Kramer, who was not involved in the research review.
And some women lost more than the average of 1.3 pounds, Streuling told Reuters Health —specifically, women who were overweight or obese before pregnancy.
"To prevent high (weight gain), pregnant women should be physically active," Streuling noted in an e-mail to Reuters Health.
The findings appear in the pregnancy journal BJOG.
They performed another analysis that included studies that combined physical activity and dietary counseling, and found women who followed this program gained almost three pounds less while pregnant.
Kramer co-authored a recent study that also reviewed previous research about the effect of exercise on pregnancy. That study "essentially found the same thing," but the results were too weak to rule out whether the trend could have been due to random chance, not a true effect of exercise on pregnancy, Kramer noted.
It's not hugely surprising that exercise alone would have only a small impact on weight gain in pregnancy, he explained — what really matters is not only how much women work out, but also how much they eat. "If you do a lot of exercise, you're going to get hungrier. So unless you cut down on what you eat, you're not going to lose weight."
In addition, not all of the included studies were of high quality, Streuling noted, and some women not assigned to the exercise program may have been overall more active in their daily lives, which may also help explain why exercise appeared to have little effect on weight in pregnancy.
Even if exercise is generally safe in pregnancy, extreme contact sports and other intense exercise such as marathons and the Iron Man are probably not a good idea, added Kramer.