NEW YORK (Reuters Health) – The Institute of Medicine and the National Research Council of the National Academies Has issued new guidelines on appropriate weight gain during pregnancy.

The new guidelines update pregnancy weight gain recommendations the IOM issued in 1990 and take into account changing US demographics, particularly the increasing percentage of women who are overweight or obese, the guideline committee notes.

According to the new guidelines, healthy American women with a normal body mass index (BMI) of 18.5 to 24.9 should gain 25-35 pounds (11.5-16 kg) during pregnancy.

The report recommends that underweight women (BMI less than 18.5) should gain 28-40 pounds (12.5-18 kg), and overweight women (BMI of 25 to 29.9) should gain 15-25 pounds (7-11.5 kg).

For obese women (BMI greater than 30), the new guidelines specify a “relatively narrow range” of recommended pregnancy weight gain between 11-20 pounds (5-9 kg).

“This report gives women and their health care providers an evidence-based answer to the question of how much weight women should gain during pregnancy,” Kathleen M. Rasmussen of Cornell University in Ithaca, New York and chair of the committee that wrote the report, said in a prepared statement.

“We call on health professionals to adopt these guidelines and help women follow them so that mothers and their children will have the best health outcomes possible,” she added.

While the report focuses on weight changes during pregnancy, it also notes that maternal weight at conception also affects infants and mothers. “Evidence from the scientific literature is remarkably clear that prepregnancy BMI is an independent predictor of many adverse outcomes of pregnancy,” the committee wrote. As a result, women should strive to enter pregnancy with a BMI in the normal weight category, they state.

The committee also emphasizes that the new guidelines are intended for American women. “They may be applicable to women in other developed countries. However, they are not intended for use in areas of the world where women are substantially shorter or thinner than American women or where adequate obstetric services are unavailable.”

Copies of the report, “Weight Gain During Pregnancy: Reexamining the Guidelines”, are available from the National Academies Press, at http://www.nap.edu.