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Obese Women Should Not Gain Weight During Pregnancy, Study Suggests

For the past 50 years, advice to women about weight gain during pregnancy has gone from fat to thin and back. First, women were told to restrict their weight gain, but many of them then had small babies. So in 1986, U.S. obstetricians began to advise women to gain between 10 and 15 kilos while pregnant. They thought this would reduce the number of low-birth-weight babies.

But all that advice is getting revised as more women having babies today are already overweight. A new study suggests that how much a pregnant woman eats isn't as important as how well she eats.

Dr. Yvonne Thornton was taught that women should gain weight when she trained as an obstetrician close to 30 years ago, but she began thinking that it was time that advice changed, especially because so many of the women she sees in her office now are grossly overweight when they're starting pregnancy.

"These ladies are coming in over 200 pounds, some 300, some 400 pounds in their pregnancy. And we're asking them to gain at least 15 pounds?" Thornton asks.

"That is what started my concerns about entering this hallowed, sacred ground of talking to pregnant women and making sure they are eating well, not twice as much, but twice as well."

Thornton asked 232 women to be part of a study where she would monitor their weight as they went through the nine months of pregnancy. All of the women were overweight or obese.

She told half the women to simply eat when they were hungry - the usual advice for pregnant women. They also received some nutritional counseling. This was the control group.

"The study group, however, was told that they needed to, one, see a nutritionist. Number two, they had a calorie-appropriate diet that was designed specifically for them, and they had to write down everything that they ate and drank during the day," Thornton says.

The women brought the diaries back to Thornton for her review during prenatal visits.

She says her research is the first study of its kind to compare weight gain strategies during pregnancy. And the women in the study group only gained 5 kilos on average, while the women in the control group gained, on average, 14 kilos.

"The patients in the study group not only gained less weight, but they also had less heavier babies," she says.

"The babies were less than 10 pounds in the study group. They had less Caesarean deliveries. They developed less gestational diabetes. They retained less weight at the six-weeks postpartum visit, and it was a win-win situation for those patients in the study group."

Recently, the U.S. Institute of Medicine revised its guidelines for weight gain during pregnancy, but Thornton says it is still telling women to gain too much weight. She says the institute needs to take data like those from her study into account when making recommendations to obese women and tell them to eat better, not more, while they're pregnant.

Her study is published in the Journal of the National Medical Association.