Less Weight Gain in Pregnancy Suggested for Obese Women

ST. LOUIS, Oct. 2 -- Many pregnant obese women should gain less weight than currently recommended and women who are severely obese should actually lose weight during pregnancy, researchers here said.

Women with a prepregnancy body mass index of 30 to 34.9 kg/m² should gain no more than 10 to 25 pounds during pregnancy to minimize the risk of preeclampsia, Caesarean delivery, and an infant who's large or small for gestational age, according to the findings of a cohort study in the October issue of the journal Obstetrics & Gynecology.

However, women with a BMI of 35 to 39.9 kg/m² should gain no more than 9 pounds and women with a BMI of 40 kg/m² or more should lose up to 9 pounds to achieve the best outcomes, reported Raul Artal, M.D., of Saint Louis University, and colleagues.

Current Institute of Medicine (IOM) guidelines for obese women advise weight gain of at least 15 pounds without an upper limit or distinguishing between levels of obesity.

Reevaluating these guidelines, the researchers said, could have important clinical and public health implications because of the increasing prevalence of obesity among women of childbearing age, the tendency for weight retention after birth, and the high prevalence of perinatal complications with obesity.

However, half of pregnant women already gain more gestational weight than the IOM recommends, commented Patrick M. Catalano, M.D., of Case Western Reserve University in Cleveland, Ohio, in an accompanying editorial.

So "encouraging pregnant women to stay within the current guidelines alone will be a significant challenge," he said.

The researchers conducted a population-based cohort study of all 120,251 obese women who gave birth at term to a single live child as recorded in the Missouri linked birth-death certificate registry from 1990 through 2001.

Women self-reported prepregnancy weight and height on the birth certificate. Among them, 59% were class I obese (BMI 30 to 34.9 kg/m²), 25% were class II obese (35 to 39.9 kg/m²), and 16% were class III obese (40 kg/m² or higher).

During pregnancy, 23% of the women gained less than 15 pounds, 31% gained 15 to 25 pounds, and 46% gained more.

Compared with women who gained 15 to 25 pounds during their pregnancies, women in all three obesity classes who had smaller weight gain had lower odds of preeclampsia, Caesarean delivery, and large babies for gestational age. Higher odds of all three outcomes were seen with weight gain greater than 25 pounds across BMI groups.

The opposite trend was seen for delivery of babies who were small for gestational age. Compared with women who gained 15 to 25 pounds, women were more likely to deliver small babies if their weight gain was less than 15 pounds but less likely to deliver small babies with a gestational gain greater than 25 pounds.

This reflects the reason for the IOM guidelines, Dr. Catalano said, noting that those guidelines were "written at a time when concern was focused on the low birth weight infant."

Notably, "the magnitude of the association for each outcome differed by obesity classification, even after adjusting for known or suspected confounders," the researchers wrote.

If clinicians could keep gain to less than 15 pounds by counseling and monitoring gestational weight, they would have the following impact:

• Prevent one case of preeclampsia for every 29 class I, 26 class II, or 20 class III obese women treated.
• Prevent one case of Caesarean delivery for every 17 women of any obesity class.
• Influence risk in one case of small-for-gestational-age birth for every 21 class I, 28 class II, or 52 class III obese women treated.
• Prevent one large-for-gestational-age birth for every 14 class I or 13 class II or III obese women treated.

Until more evidence is available on what might be a reasonable goal for obese women during pregnancy, Dr. Catalano recommended that physicians advise these women to follow a balanced diet with a moderate exercise regimen, possibly with support of a registered dietician.

"The problem of obesity in our society will not be solved by the obstetrician-gynecologist; it is a public health issue," he concluded.

"However, as health care providers to young women," he added, "we are in a unique position to affect both short- and long-term risks and morbidities for our patients and families at a time when they may be most amenable to alterations in lifestyle."

The authors noted that the study "shows only statistical associations and does not imply causality. The latter can only be achieved by conducting a prospective randomized controlled trial of obese women to determine the effect of controlled gestational weight gain on specific pregnancy outcomes."