LITTLE FALLS, N.J., May 28 - Obese women should gain only 11 to 20 pounds during pregnancy, according to updated guidelines from the Institute of Medicine.

The recommendation builds on the agency’s earlier guidelines that recommend a weight gain of 15 to 25 pounds for overweight women, 25 to 35 pounds for normal women, and 28 to 40 pounds for underweight women.

Researchers have included recommendations for obese women since body mass index (BMI) and gestational weight gain have increased among women across the country.

The update also uses the World Health Organization and National Heart, Lung, and Blood Institute ranges for BMI instead of the Metropolitan Life Insurance tables used in the 1990 recommendations.

The new ranges are more conservative, with the underweight BMI category starting at 18.5 instead of 19.8.

“Because of the shift in BMI in the population towards more overweight and obese, those criteria have shifted now for the obese category,” said Patrick M. Catalano, M.D., of Case Western Reserve, a member guideline committee. “With the new criteria, we’re just trying to be consistent with what everybody else is using.”

The guidelines are “not dramatically different from what was reported in 1990, but they are sort of progressive,” said Michael Katz, M.D., senior vice president for research at the March of Dimes, a co-sponsor of the study.

“They illustrate the substantial increase in obesity,” Dr. Katz said.

Dr. Catalano said it would be easier to achieve the recommendations if women try to get within normal BMI range when they’re trying to conceive.

This will result in better outcomes for both mom and baby, he said, since it is “remarkably clear that pre-pregnancy BMI is an independent predictor of many adverse outcomes.”

Interventions in diet and exercise - both before and during pregnancy - will be essential in assisting women in meeting the guidelines, especially those who are obese, he said.

“The idea is that it will require an effort by many people,” Dr. Catalano said. “It’s not just something that one healthcare provider during pregnancy can do. It includes a host of other people including a nutritionist, dietician, and even an exercise physiologist.”

Dr. Katz said the aims of the report are laudable, but “the effects are very difficult to achieve.”

“Here the motivation is stronger because [pregnant women] are strongly motivated to protect their child,” he said. “But to have a concerted effort like this will be difficult.”

While Dr. Katz said the new guidelines are more conservative than those past, others say they are not conservative enough.

“It’s been well shown that such a patient can lose weight in pregnancy and still be fine,” said Jacques Moritz, M.D., of St. Luke’s-Roosevelt Hospital in New York.

“[The guidelines] are still concerned with small babies. That was a problem when women smoked and drank in pregnancy. Now it’s just the opposite.”

“Women don’t need to eat for two, but for 1.1,” he said.

The authors of the new recommendations argued that mother and child can achieve good outcomes “within a range of weight gains.” Also, physicians should consider different factors for individual women, they said.

That means the guidelines should be used “in concert with good clinical judgment as well as a discussion between the woman and her healthcare provider about diet and exercise,” they said.

The report also calls for further study of pregnancy in obese women, as well as the impacts of gestational weight gain on maternal and child outcomes.

The researchers said they believed the new recommendations should be applicable to all women, across all racial or ethnic groups, but recommended additional research to confirm the hypothesis.

Other updates include:

  * Short women don’t need to limit weight gain to the lower end of the range for their pre-pregnant BMI. The researchers said there was insufficient evidence to continue this 1990 recommendation.
  * There is no continued support for lower-range weight gains in women under 20, as younger women and adolescents often need to gain more to improve birth outcomes.
  * Though there was less evidence for twins than singletons, researchers said normal weight women expecting twins should gain 37 to 54 pounds, while overweight women should gain 31 to 50 pounds, and obese women, 25 to 42 pounds. There was insufficient information for underweight women.

Primary source: Institute of Medicine
Source reference:
Rasmussen KM, Yaktine AL “Weight gain during pregnancy: Reexamining the guidelines” National Academies Press 2009.