"The message is not getting out that women should continue to exercise during pregnancy, at least at moderate intensity," said Terry Leet, Ph.D., a study author and associate professor of community health at Saint Louis University School of Public Health.
"Only one of every six pregnant women are meeting the current physical activity recommendation of 30 or more minutes of moderate physical activity on most, if not all, days of the week."
The research, funded by the Centers for Disease Control and Prevention, was published in Medicine & Science in Sports & Exercise.
The findings support a recent newsletter article by Raul Artal, M.D., lead author of the American College of Obstetrics and Gynecology's 2002 guidelines for exercise during pregnancy and chair of the department of obstetrics and gynecology at Saint Louis University.
Artal said that not enough of his fellow obstetricians encourage their healthy patients to exercise during pregnancy.
"The hesitance of obstetricians to recommend exercise to pregnant women is rooted in old-fashioned notions of pregnancy as a time of confinement," Artal wrote in the September issue of Ob.Gyn News, a publication for obstetricians and gynecologists.
Saint Louis University School of Public Health researchers found that pregnant women were not as physically active as women who were not pregnant. They analyzed data from more than 150,000 pregnant and non-pregnant women who were interviewed by phone in 1994, 1996, 1998 and 2000.
Only 16 percent of pregnant women and 27 percent of non-pregnant women were meeting the current physical activity recommendation in 2000.
Further, the percentage of pregnant women who said they exercised at a moderate or vigorous level was lower in 2000 than in any of the previous years.
Brisk walking for 30 or more minutes at least five days a week is considered moderate exercise and meets the current physical activity recommendation for pregnant and non-pregnant women. Leet and his colleagues found that pregnant women who were older, non-white, unmarried, current smokers, had low incomes or less than 12 years of education were less likely to exercise than others.
"Overall, this study has vital public health implications that can assist physicians to identify patients who are at high risk for inactivity during pregnancy," Leet said.
"These women should be encouraged to begin moderate activities most, if not all days of the week, as long as medical or obstetric complications do not exist."
The study found that walking was the most common form of physical activity among all women surveyed. Other common physical activities were swimming and dance aerobics.
Saint Louis University School of Public Health is one of only 37 fully accredited schools of public health in the United States and the nation's only School of Public Health sponsored by a Jesuit university.