In fact, researchers found, obese women who maintained their weight or shed pounds during pregnancy were more likely to have a normal-weight newborn than those who gained pregnancy pounds.

The notion that it's all right for obese women to avoid weight gain during pregnancy is fairly controversial, said Dr. Raul Artal, an obstetrician at St. Louis University and the lead author of the new study.

Most obstetricians follow guidelines devised in 1990 that recommend obese women gain about 13 pounds during pregnancy. That's far less than the 25 to 35 pounds recommended for normal-weight women, but still a substantial amount of weight for women who are already heavy.

Those guidelines deserve a second look, Artal argued. For obese women, he said, weight maintenance or even modest weight loss may not only do no harm to mother and child, but might benefit them.

Because it's so difficult for obese women to shed pounds gained during pregnancy, Artal said, preventing the weight gain could bring longer-term health benefits.

"Pregnancy is not a state of confinement," he said, and overweight women should not be afraid of moderate physical activity. "All we're talking about is a brief walk after each meal," Artal noted.

That said, he advised that pregnant women still talk to their doctors before taking up an exercise routine, to make sure they have no conditions that preclude physical activity. Women should also get advice from a nutritionist on how to make healthy diet changes.

Source: Applied Physiology, Nutrition, and Metabolism