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Findings challenge American College of Obstetricians and Gynecologists pregnancy guidelines

VALHALLA, N.Y., June 2, 2009 — 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.” The Institute of Medicine (IOM) recommends 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, wellbalanced, 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.

The IOM and the National Research Council (NRC) have undertaken a study to review and update the 1990 IOM recommendations for weight gain during pregnancy. The IOM-NRC findings are expected to be released this month.

Dr. Thornton’s paper, “Perinatal Outcomes in Nutritionally Monitored Obese Pregnant Women: A Randomized Clinical Trial,” was published in the June issue of the Journal of the National Medical Association. Her co-authors include Claudia Smarkola, PhD, Sharon M. Kopacz, MD, and Sabriya B. Ishoof, MD.


Yvonne S. Thornton, MD, MPH
Dr. Thornton is a clinical professor of obstetrics and gynecology and board-certified specialist in obstetrics, gynecology and maternal-fetal medicine at New York Medical College, Valhalla, N.Y.

She received her M.D. with honors from the Columbia University College of Physicians and Surgeons in 1973. After earning her medical degree, she completed a residency in obstetrics and gynecology at Roosevelt Hospital in New York City. Dr. Thornton then completed a post-doctoral fellowship in maternal-fetal medicine at Sloane Hospital for Women and Babies Hospital at Columbia-Presbyterian Medical Center. Following her postdoctoral training, she served as a Lieutenant Commander in the United States Navy stationed at Bethesda (Hospital of the President).

Dr. Thornton also holds an Executive Masters (M.P.H.) degree in health policy and management from the Columbia University School of Public Health and is the recipient of several honorary degrees, including a doctoral degree (Sc.D.) from Tuskegee University. During her 35-year career in medicine, she has served on the faculties of the Uniformed Services University of the Health Sciences, Cornell University Medical College, and Columbia University College of Physicians and Surgeons. She joined the faculty of New York Medical College in 2008.

Dr. Thornton has conducted research on various aspects of maternal-fetal medicine at The Rockefeller University, the National Institutes of Health Pregnancy Research Branch, National Naval Medical Center, Naval Medical Research Institute, and New York Hospital- Cornell Medical Center. She is the author or co-author of more than a dozen scientific papers and serves as a reviewer for the American Journal of Obstetrics and Gynecology.

She is a member of the Association of Women Surgeons, a life member of the New York Academy of Medicine, and a fellow of the American College of Obstetricians and Gynecologists and the American College of Surgeons. Dr. Thornton was the first black woman in the United States to be board-certified in high-risk obstetrics and to be accepted into the New York Obstetrical Society.

Before her career in medicine, Dr. Thornton performed with her family orchestra, known as "The Thornton Sisters," throughout high school, college, medical school, and residency, appearing at Harlem’s Apollo Theater and on the Ted Mack Amateur Hour, among many other venues.

Dr. Thornton is the national bestselling author of The Ditchdigger's Daughters, her family’s biography, which was made into an award-winning movie for cable television.