Obese women should not gain weight during pregnancy

May 31 2009

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." Until its revised guidelines were released, the Institute of Medicine (IOM) had recommended that overweight women should gain about 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."

The study grew out of Dr. Thornton's personal experience with obesity and pregnancy. Despite being overweight, she gained a substantial amount of weight during her first pregnancy, exacerbating her life-long battle with obesity. During her second pregnancy, she followed a well-balanced diet and gained little weight, with no adverse consequences for mother or baby.

Dr. Thornton observed the same pattern in her own clinical practice, leading her to question prevailing guidelines for weight gain during pregnancy. Adding to her skepticism was the fact that women who develop gestational diabetes are routinely put on diets that effectively limit weight gain, with no ill effects.

"It is the mindset of our specialty, and our society, that we need to have round, chubby pregnant women in order make sure they are healthy," adds Dr. Thornton. "Pregnancy has become a license to eat. We talk about 'eating for two,' but it's really more like eating for 1 and 1/20th."

These attitudes have contributed to the obesity epidemic in the U.S., where 35 percent of women are considered obese, says the researcher. The situation is even worse among African-American women, four out of five of whom are overweight or obese.

"Gaining weight during pregnancy contributes to obesity, and it makes it that much harder for overweight women to return to their normal weight after pregnancy," says Dr. Thornton.