The Institute of Medicine (IOM), the nation's most influential medical advisory group, has updated its guidelines for weight gain during pregnancy for the first time since 1990.
The revised recommendations, released May 28, which also include the first advice regarding exercise during pregnancy, reflect new data on prenatal health as well as several recent shifts in the obstetric landscape pregnant women in the U.S. are now older, more likely to deliver multiple births and ethnically more diverse than they were 20 or 30 years ago. But far and away, the IOM's greatest new concern is the increased population of overweight and obese mothers-to-be. (Watch TIME's video "How to Lose Hundreds of Pounds.")
For centuries, one of the greatest dangers pregnant women faced was not gaining enough weight to adequately nourish a healthy baby. To protect against malnutrition and, in some cases, a strong societal pressure to stay thin, doctors and grandmothers everywhere routinely urged expecting mothers to eat, eat, eat.
Times have changed. Today, nearly two-thirds of American women of childbearing age are overweight, and one-third qualify as obese. An abundance of research suggests that weight gain before and during pregnancy increases the risk of several serious health complications for both mother and child, including diabetes, hypertension and birth defects.
"Increasingly, we saw the weight women were gaining was going outside the established guidelines, either below or above them," says Kathleen Rasmussen, a professor of nutrition at Cornell University and the chair of the committee that wrote the IOM report. "That suggested a need to re-examine them." (Watch a video on fitness gadgets.)
For most women including those who are underweight, normal weight or even overweight at conception the guidelines remain unchanged from the original 1990 standards: women with a healthy body mass index, or BMI (a ratio of height and weight used to define obesity), of 18 to 25 are advised to gain 25 to 35 pounds during pregnancy. Overweight women with a BMI of 25 to 29.5 should gain less, up to 25 pounds; underweight women, with BMIs below 18.5, should gain more, up to 40 pounds.
The recommendations include new, specific guidelines for obese women, including those who have a BMI of 30 or higher at conception. These mothers-to-be are advised to limit their weight gain to 11 to 20 pounds. The standards also suggest for the first time that pregnant women may safely exercise up to 30 minutes a day throughout their entire pregnancy, barring any complications.
Failing to adhere to the IOM's recommendations could increase health risks for both mother and child, Rasmussen says. Women who do not gain enough weight during pregnancy face an increased risk of stunted fetal growth and preterm delivery. But more commonly, women put on too many extra pounds: approximately 40% of normal-weight and 60% of overweight women gained excessive weight during pregnancy, according to a study published in March by the Centers for Disease Control and Prevention; one-fourth of obese women gained more than 35 pounds, the recommended limit for women of healthy weight. (Watch TIME's video "Uninsured Again.")
Studies have linked obesity and rapid weight gain during pregnancy to a higher risk of gestational diabetes and hypertension in the mother. And because most women fail to shed all their pregnancy fat, the additional weight can lead to an increased risk of postpartum obesity, along with elevated risks of heart disease and stroke. Babies delivered by obese women tend to be born bigger, earlier and by Cesarean section. And many studies suggest that a mother's gestational obesity predicts later weight problems in her offspring. One recent study conducted by researchers at Harvard Medical School found that among nearly 12,000 children and teenagers, those whose mothers gained more than the recommended amount of weight during pregnancy were 42% more likely to be obese by the time they were 9 to 14 years old.
Rasmussen emphasizes that physicians must do more to counsel individual patients about diet and exercise both before and after conception. "Traditionally, these guidelines concentrated on what was healthiest for the baby," Rasmussen says. "Here, we've spent much more time looking at both the mother's and the baby's well-being."
But the new recommendations should be applied only to American patients, the IOM says. Although the guidelines use globally accepted BMI cutoffs determined by the World Health Organization to define pre-pregnancy obesity, the weight-gain recommendations may not be appropriate for women in other countries, who are shorter or thinner or have inadequate prenatal care.
Some American doctors think the IOM, which is part of the National Academy of Sciences, could have gone even further in its recommendations for overweight women. Dr. Raul Artal, a professor of obstetrics at St. Louis University's School of Medicine, believes that more attention needs to be paid to the long-term health risks of maternal obesity for both mother and child, and that these concerns are far more important than any gestational weight-gain chart. Artal runs a clinic specializing in obese and overweight pregnancies and has found that, under the close guidance of dietitians and physicians, about half of his oversize patients put on little to no weight and deliver healthy, normal-weight babies. "Obesity leads to lifelong problems that this committee still fails to recognize the full importance of," he says. "They remain much more concerned about not-sufficient weight gain."
Still, Artal applauds the updated guidelines, which he calls an "excellent review of all the relevant research" and which are more accommodating of individual patients. "The reality is that no two pregnancies are alike, so flexibility is important," Artal says. These days, it seems, the age-old advice for mothers-to-be to "eat for two" no longer applies.