Such data on the increasing girth of pregnant women and the growing rates of obesity in children led to pressure on the Institute of Medicine to revise a set of 1990 guidelines that were written primarily to prevent excessively low infant birth weights. Numerous medical journal articles in recent years have called the guidelines irrelevant to today's obstetrics patients.
The panel said that the existing guidelines were essentially fine. It's women and their doctors, the members said, who need to try harder -- often much harder -- to help the women reach a normal weight before pregnancy and avoid excessive weight gain during pregnancy.
"Although not dramatically different, fully implementing the guidelines will represent a change in the care provided to women of childbearing age," said Kathleen Rasmussen, chairwoman of the committee and a professor of nutrition at Cornell University.
The report was requested by six major health organizations so that doctors could better advise and care for their patients. Although nothing in the report is mandatory, healthcare professionals are expected to acknowledge and implement at least some of the panel's recommendations.
But several leading experts on maternal obesity and child health expressed disappointment with the document. A growing contingent of doctors says that obese women -- which includes one in every five pregnant women -- should gain little or no weight.
"In my opinion, the Institute of Medicine is missing an opportunity to address the issue of the obesity epidemic and the contribution that pregnancy makes to that epidemic," said Dr. Raul Artal, chairman of the department of obstetrics, gynecology and women's health at St. Louis University.
The recommendations call for a gestational weight gain of 28-40 pounds for underweight women, 25-35 pounds for women of normal weight, 15-25 pounds for overweight women and 11-20 pounds for obese women. The only change is for obese women, who were previously advised to gain at least 15 pounds, with no upper limit.
The problem is not the guidelines, but the failure to adhere to them and to address obesity in reproductive-age women, said Dr. Maxine Hayes, state health officer for the Washington State Department of Health and chairwoman of a 2006 panel that urged a reexamination of the guidelines. "If we wait for every woman to be advised about weight gain after they become pregnant, it's too late. It puts women and their babies on a trajectory that is unhealthy."
During the two-year process of reexamining the guidelines, committee members tried to balance the health needs of the fetus with the health needs of the mother, Rasmussen said, ultimately deciding that the recommendations were largely up-to-date already.
Not all experts in maternal-fetal health are convinced.
"We have been doing this same recommendation for 19 years, and it has been very unsuccessful," said Susan Y. Chu, a senior epidemiologist at the Centers for Disease Control and Prevention who has studied gestational weight gain. "But they did what was most critical, which was to put a cap on the obese category."
Several studies suggest that obese women may require little weight gain as long as it's clear that the fetus is growing.
"We have determined that overweight and obese women can benefit and have better pregnancy outcomes if they limit their weight gain," said Artal, the author of several studies on obese pregnant women. "The committee was cautious. They were concerned they might cause harm. But by maintaining the status quo, I think that may cause more harm."
A study in the June issue of the Journal of the National Medical Assn. found that obese pregnant women who followed well-balanced diets and gained little or no weight had better outcomes -- as did their babies -- than women who gained more weight.
That study's lead author, Dr. Yvonne S. Thornton, a professor of obstetrics and gynecology at New York Medical College, said the committee may have feared an increase in births of underweight infants if more pregnant women were placed on restricted diets. "This is a litigious society," she said. "If we did restrict calories and there was an untoward outcome, people might say, 'Well, you didn't feed me enough.' "
The suggested weight range of 11 to 20 pounds for obese women is aimed at women in the lower ranges of the obesity category, defined by a body mass index of 30 to 35, Rasmussen said. There is little data to guide recommendations for women in the higher ranges of obesity, she said. About 8% of women of childbearing age are morbidly obese, with a BMI of 40 or more.
Some doctors criticized the report's call for diet and exercise counseling as unrealistic. Few health insurance plans pay for such counseling, and doctors do not have the time to provide it, Hayes said.
However, the report was praised for its emphasis on exercise. "One can't look at diet alone," Artal said. "Exercise is very much a part of a healthy lifestyle during pregnancy."
The committee also called for more studies on gestational weight gain, including asking states to adopt a birth certificate that gathers information on weight before and during pregnancy.