Traditionally, doctors haven't liked to see pregnant women lose weight, even if the women are obese. Indeed, the 1990 guidelines of the Institute of Medicine (IOM) suggest that obese women should gain 15 to 25 pounds over the course of a pregnancy.
Yet children born to obese women have increased risk of neural tube defects, congenital heart defects, and other serious problems. And most women don't lose all the weight they gain during pregnancy -- adding to the health risks of women already battling obesity.
This has led some doctors to question whether it might be better for obese women to maintain their weight -- or even lose weight -- during pregnancy.
One of those doctors is Raul Artal, MD, professor and chairman of the department of obstetrics, gynecology, and women's health at Saint Louis University School of Medicine. To begin studying the issue, Artal and colleagues worked with 96 obese or morbidly obese pregnant women with gestational diabetes.
The women in the study were allowed to choose either a reduced-calorie diet alone or a weight-maintenance diet plus exercise -- walking for at least 20 minutes after each meal.
Nearly half the women in the exercise group maintained their weight or lost weight, while four out of five women in the diet-only group gained weight.
"Women who either maintain weight in pregnancy or lose weight -- and exercise -- have fewer complications than those on diets alone," Artal tells WebMD. "We definitely see these women deliver normal-size babies, which means that this plays a role in fewer complications."
Does this prove it's safe for obese women to lose weight during pregnancy?
No, says J. Christopher Glantz, MD, MPH, professor of obstetrics and gynecology at the University of Rochester, N.Y. He notes that the Artal study was too small and too limited in scope to apply to all obese women during pregnancy.
But the study does suggest that the dogma "weight gain during pregnancy is always good" should be re-examined, says Glantz, who was not involved in the Artal study.
"My own experience is the babies do well whether obese women gain zero pounds or the 15 pounds the IOM recommended," Glantz tells WebMD. "For women in the higher obesity categories, it isn't a problem even if they lose weight."
Artal stresses the importance of exercise during pregnancy -- particularly for obese women.
"We know that exercise in pregnancy is safe for everybody," Artal says. "When we talk exercise, we talk about just walking -- a safe form of exercise. If obese, pregnant women can engage in walking at a moderate pace, it is probably more beneficial. And maintaining a lower-calorie diet is beneficial."
The bottom line, Artal says, is that we all must get over the idea that pregnancy is a time for inactivity and overeating.
"The message should be that pregnancy is not a state of confinement -- and you should not eat for two," he says.