Study Suggests Obese Women Should Not Gain Weight During Pregnancy

A new study challenges the prevailing wisdom that to improve pregnancy outcomes, all women, even those who are obese, should gain weight during pregnancy. The study, the first of its kind, found that obese pregnant women who followed a well-balanced diet and gained little or no weight had maternal-fetal outcomes that were equal to or better than those who gained substantial weight. The findings appear in the June issue of The Journal of the National Medical Association.

For years, doctors and other health-care providers have managed pregnant patients according to guidelines issued by the American College of Obstetricians and Gynecologists (ACOG). In 1986, ACOG stated, “Regardless of how much women weigh before they become pregnant, gaining between 26-35 pounds during pregnancy can improve the outcome of pregnancy and reduce their chances of having the pregnancy end in fetal death.” In 1990, the Institute of Medicine (IOM) recommended that overweight women should gain at least 15 pounds during pregnancy.

The current study was undertaken to test whether these guidelines make a difference in maternal-fetal outcomes among obese women.

In the study, conducted at several hospitals, the researchers followed 232 obese pregnant women, all of whom had a body mass index (BMI) of 30 or greater. Half of the women followed conventional prenatal nutritional guidelines, which is essentially “eat to appetite” (control group). The other half were placed on a well-balanced, nutritionally monitored program, which included a daily food diary (study group). The average weight gain in the control group was 31 pounds, compared to 11 pounds in the study group. Twenty-three extremely obese patients lost weight during their pregnancy.

The findings showed that there were no fetal deaths and no growth-restricted infants in the study group. Also, there were fewer babies weighing more than 10 pounds in the study group than in the control group. (A birth weight over 10 pounds poses significant hazards to both infants and mothers.) Moreover, women in the study group gained less weight, had fewer cesarean deliveries, were less likely to develop gestational diabetes, and retained less weight after they delivered than women in the control group.

The researchers concluded that obese pregnant women may be placed on a healthy, well-balanced, monitored nutritional program without adverse maternal-fetal outcomes.

“Women who are obese when beginning a pregnancy are, by definition, unhealthy,” says study leader Yvonne S. Thornton, MD, MPH, a clinical professor of obstetrics and gynecology and board-certified specialist in maternal-fetal medicine at New York Medical College. “To say that they should gain even more weight is counter-intuitive, and our study bears that out. Rather than focusing on numerical endpoints with respect to weight gain, we need to focus on making these women healthier by getting them to eat a well-balanced diet.”