June 6 (HealthDay News) -- Contrary to previous research, a new study says that stretching may be more effective than walking or rigorous exercise at reducing the risk of preeclampsia in certain women.

The findings, by researchers at the University of North Carolina at Chapel Hill School of Nursing, apply only to women who were not physically active before becoming pregnant and who have experienced preeclampsia before.

Up to 8 percent of pregnant women experience preeclampsia, or pregnancy-induced hypertension, putting the condition among the leading causes of maternal and fetal illness and death worldwide. In preeclampsia, blood pressure sharply increases (readings of 140/90 or higher must occur twice within six hours) and swelling and kidney problems may also result.

The findings, presented last week at the annual meeting of the American College of Sports Medicine, in Indianapolis, were expected to be published in the spring issue of  Hypertension in Pregnancy.

The study looked at 79 women with a previous preeclampsia diagnosis and a sedentary lifestyle. During the 18th week of pregnancy, about half of the women were randomly assigned to a group that exercised by walking 40 minutes five times a week at moderate intensity; the other group performed slow, non-aerobic stretching along to a 40-minute video five times a week.

Almost 15 percent of women in the walking group developed preeclampsia by the end of their pregnancy, while less than 5 percent of the stretching group developed the condition. While the incidence of preeclampsia among the walkers matched that of high-risk pregnancies in general, the rate among the stretching group was close to that one found in the general population.

"Clearly, walking does not have a harmful effect during pregnancy," lead researcher SeonAe Yeo, an associate professor with a specialty in women's health at the UNC School of Nursing, said in a prepared statement. "But for women who are at high risk for preeclampsia, our results may suggest that stretching exercises may have a protective effect against the condition."

Yeo said she thought stretching produced more transferrin, a plasma protein that transports iron through the blood and protects against oxidative stress on the body, and that helps guard against preeclampsia.

Based on the finding, prenatal care providers may want to recommend exercise plans based on an individual pregnant woman's needs and abilities, Yeo said.

SOURCE: University of North Carolina at Chapel Hill, news release, May 28, 2008