Exercise Cuts Rate of Diabetes In Pregnancy Among Morbidly Obese Women

BUFFALO, N.Y. -- Extremely overweight women who become pregnant can cut their risk of developing gestational diabetes by taking part in moderate physical activity, a new study has shown.

The study is published in the Dec. 2 issue of the American Journal of Epidemiology, which is dedicated to research by faculty members and graduates of the UB Department of Social and Preventive Medicine.

Gestational diabetes, the most common medical complication of pregnancy, often is related to obesity. It can be a serious threat to the baby, increasing the risk of traumatic delivery, stress in labor and neonatal complications.

Exercise has been shown to have a beneficial effect on insulin resistance, a prelude to gestational, as well as overt, diabetes, by making insulin receptors more sensitive to insulin in the blood stream. However, study results showed exercise appeared to have no beneficial effect on the risk of developing the disease among women who were not morbidly obese before becoming pregnant.

In an interesting twist, the findings showed that morbidly obese women with private insurance, considered an indicator of socioeconomic status, were much more likely to develop gestational diabetes than their counterparts covered by Medicaid.

Timothy D. Dye, Ph.D., lead author on the study, holds a master's degree in epidemiology and a doctorate in anthropology from UB. He is an associate professor of community and preventive medicine at the University of Rochester and director of UR's Division of Public Health Practice. Raul Artal, M.D., professor of obstetrics and gynecology at SUNY Health Science Center at Syracuse, was co-author and lead physician on the study.

"Diabetes is a tremendous problem in this country," Artal said. "In some populations, 50 percent of the people are affected. In others, the prevalence is more like 10-14 percent. If there is an intervention that works, even if it is just in this morbidly obese population of pregnant women, it could be very useful."

Obesity also is a major health problem in the U.S., Dye said, noting that the researchers were surprised at the number of overweight women in their study population of 12,799.

"We were struck by the prevalence of obesity, which was very high, and the frequency of exercise, which was very low," he said. "Thirteen percent had a high body mass index (BMI), another 10 percent had obese BMIs and another 10 percent had morbidly obese BMIs, which means one-third of women were significantly overweight before they became pregnant."

The BMI is a measure of relative weight, calculated by dividing weight in kilograms by height in meters squared.

Data for the study were collected from the Central New York Regional Perinatal Data System, containing all live-birth records from a 15-county region. Women who gave birth between Oct. 1, 1995 and July 31, 1996 were eligible to participate in the study. Researchers excluded women who had conditions that ruled out exercise during pregnancy.

Information on gestational diabetes status, defined as glucose intolerance that developed or was discovered during the current pregnancy, and BMI before pregnancy came from medical records.

Researchers contacted participants personally to collect information on the number of times they exercised for at least 30 minutes beyond their normal activity per week. Participants then were classified as either exercisers or non-exercisers.

Results of the analysis of the relationship between physical activity, obesity and gestational diabetes showed no effect of exercise on diabetes risk among women in the first four categories of body mass index. However, women who were morbidly obese, with a BMI of 33 or greater (the optimum BMI for women is 20-25) and who did not exercise, were twice as likely to develop gestational diabetes than their counterparts who did exercise.

The presence or absence of exercise, not the amount or frequency, was the important factor. Results showed little difference in benefit between women who exercised once a week and those who exercised three or more times a week.

Artal also pointed out that the women did not need to enroll in a fitness program to receive the benefit. "I tell my patients to go for a walk in the shopping mall for half-an-hour to an hour a couple of times a week," he said. "That may be all they need."

The differences in the effect of exercise on diabetes rates in more- and less-affluent women may be related to diet, or other as-yet-unidentified factors that could influence the impact of exercise, Dye noted.

Additional researchers on the study were Kerry L. Knox, Ph.D., from the UR Department of Community and Preventive Medicine, and Richard H. Aubry, M.D., and Martha A. Wojtowycz, Ph.D., from the SUNY Health Science Center at Syracuse.