Safe weight gain for heavier moms-to-be depends on level of obesity, study suggests

The study, which included 5,500 obese pregnant women at Magee-Womens Hospital of UPMC, investigated levels of gestational weight gain related to three adverse outcomes: babies born too small, too large or too early. The women in the study were stratified by level of obesity, or body mass index (BMI), and defined as class 1 (BMI 30 to 34.9), class 2 (BMI 35 to 39.9) and class 3 (BMI 40 and over).

Nearly 10 percent of the study participants lost weight during pregnancy. Weight loss was generally associated with an increased risk of preterm births and infants with restricted growth. For severely obese women, however, very minimal weight gain (less than 5 pounds) or weight loss was not detrimental to newborn health.

The study also found that women who gained a large amount of weight were at increased risk of pre-term births and infants who were overgrown, suggesting that very high weight gain also is related to adverse birth outcomes.

"Some clinicians have been pushing weight restriction for all classes of obese women," said Lisa M. Bodnar, Ph.D., M.P.H., R.D., lead author of the study and assistant professor of epidemiology, obstetrics and gynecology, University of Pittsburgh. "Our study indicates that a single standard for optimal weight gain for obese women may not fit the bill. Instead, we need to consider level of obesity and advise women accordingly."

The authors suggest the following pregnancy weight gain ranges to optimize birth outcomes: 20 to 30 pounds for class 1 women; 5 to 20 pounds for class 2 women and less than 10 pounds for class 3 women. Women who gain less than the suggested amounts can still have healthy pregnancies provided their dietary intake is being monitored to ensure proper nutrition, say the authors.

"Obese women may face increased complications of pregnancy," said Barbara Abrams, Dr.P.H., R.D., senior author of the study and professor of epidemiology, maternal and child health and public health nutrition, University of California, Berkeley. "Appropriate weight gain may lessen these risks for the baby, so we strongly encourage all obese women to receive nutrition and lifestyle counseling throughout their pregnancies."

In addition to Drs. Bodnar and Abrams, authors of the study include Anna Maria Siega-Riz, Ph.D., R.D., Gillings School of Global Public Health, University of North Carolina, Chapel Hill; Hyagriv N. Simhan, M.D., and Katherine P. Himes, M.D., University of Pittsburgh School of Medicine and Magee-Womens Research Institute.

The research was supported by the National Institutes of Health.