THURSDAY, Dec. 20, 2012 (HealthDay News) -- Women who are overweight or obese should gain less weight during pregnancy than moms-to-be of normal weight, according to new recommendations by the American College of Obstetricians and Gynecologists.
The guidelines, which are based on a woman's weight before becoming pregnant, suggest that overweight women gain between 15 and 25 pounds over the last two trimesters while obese women not increase their weight by more than 11 to 20 pounds. Normal and underweight women should gain between 25 and 35 pounds and 28 and 40 pounds, respectively.
The weight categories are based on body-mass index (BMI), a calculation based on height and weight. A BMI between 18.5 and 24.9 is normal weight, between 25 and 29.9 is overweight and 30 or greater is considered obese.
The guidelines, published in the January issue of Obstetrics & Gynecology, state that the most important criterion is whether the fetus is growing well.
"The concern is that if overweight and obese women gain [too much] weight, they could be at increased risk of gestational diabetes, having a C-section and postpartum weight retention," said Dr. George Macones, a professor of obstetrics and gynecology at Washington University in St. Louis and chair of the ACOG committee that wrote the new recommendations.
Gaining too much weight during pregnancy could also lead to babies being born larger than normal, which increases their risk of obesity as children and adults.
More than 50 percent of pregnant women are overweight or obese and 8 percent of women of reproductive age are extremely obese, according to an accompanying journal article.
But if women gain too little weight, babies could be born small, and these babies could be predisposed to heart disease, diabetes and high blood pressure as children and adults, Macones said. "It's not a huge concern, there's a little bit of information in a very evolving area of science that how the baby grows in utero might be related to long-term conditions," he said.
Another expert agreed. "The tradeoff has always been that gaining less is better on the maternal end, but on the baby end there are data that gaining less could restrict fetal growth," said Dr. Emily Oken, an associate professor of population medicine at Harvard Medical School.
The ACOG guidelines for the recommended ranges of weight gain during pregnancy echo guidelines that the Institute of Medicine (IOM) put out in 2009.
However, there is more leeway in the ACOG guidelines for overweight and obese women than in those of the IOM, Macones said.
Studies published since the IOM recommendations came out have found that overweight women who gained less than the recommended amount still had babies that grew well and the mothers shed their baby weight better, Macones explained.
"[But] our overall feeling is that there isn't quite enough information to make a fair recommendation to gain absolutely less than the IOM recommendation," Macones added.
Some doctors disagree. "I think 11 to 20 pounds is way too much for an obese woman," said Dr. Thomas Myles, a professor of obstetrics and gynecology at Saint Louis University School of Medicine who was not involved in the current recommendations.
"I usually tell my [obese] patients that gaining less than 10 pounds and even losing up to 10 pounds is appropriate, whereas for overweight women, gaining 10 to 15 and even up to 20 pounds is appropriate," Myles said.
Gaining a little less weight than the recommended amount, especially for overweight and obese women, might be better, Oken said.
"Just getting to the goal [for weight gain] and not surpassing it would substantially improve a lot of women's and babies' health," Oken said. She estimates that about half of women gain more than the recommended amount of weight during pregnancy.
The best time to get within the normal weight range is before becoming pregnant, Macones said. Depending on a woman's BMI, he might suggest a weight loss program for six months prior to getting pregnant or, in extreme cases, having bariatric surgery, he said.
Women who exercise and are within the normal weight range could have an easier time getting pregnant and a smoother pregnancy and delivery, Myles said. He recommends lower-impact activities like walking and swimming for overweight women trying to get pregnant or who are pregnant.
During pregnancy, overweight and obese moms-to-be can get away with putting on fewer pounds because they have extra nutrient stores that the fetus can draw on, Macones said. "[But] they still need to make sure they're getting good nutrition," he added.
The U.S. National Heart, Lung and Blood Institute helps you calculate your BMI.