Activity may ward off preeclampsia for lean women

NEW YORK (Reuters Health) - Being physically active during pregnancy may help prevent a serious complication called preeclampsia, but the effect is small, and only seems to apply to women who are not obese, new research from Norway shows.

"The main risk factor for preeclampsia is actually a high body mass index, so reducing weight before starting to think about pregnancy is in general a very good idea," lead investigator Dr. Per Magnus of the Norwegian Institute of Public Health in Oslo, told Reuters Health. Trimming down also reduces a woman's risk of developing diabetes in pregnancy and of having a very high birthweight baby, "which is in itself a kind of complication," he added.

In preeclampsia, a woman develops high blood pressure and begins excreting protein in her urine. It occurs in up to 8 percent of pregnancies, and puts a woman at risk of stroke, seizures, premature delivery, and other complications. Past studies, in which women who developed preeclampsia were compared with women without preeclampsia, suggested that recreational physical activity could help prevent the condition.

To further investigate, Magnus and his team followed 59,573 women in the Norwegian Mother and Child Cohort Study, who gave birth to a single infant between 1999 and 2006, to see if physical activity during pregnancy influenced preeclampsia risk.

Between 14 and 22 weeks of pregnancy, the women reported how frequently they engaged in recreational physical activity, with 24 percent reporting no such activity at all.

Their findings are reported in the American Journal of Epidemiology.

The 7 percent of women who were physically active more than 25 times a month were 21 percent less likely than the inactive women to develop preeclampsia.

Using the participant's body mass index, the relationship was strongest in women who were not overweight, and no relationship was seen in women who were obese.

The study wasn't designed to look at why exercise may or may not help prevent preeclampsia. However, Magnus and his team suggest that early development of the placenta might be a key factor in the condition. Exercise may promote healthy placenta development among lean women, but it may be stressful for women who are heavier.

Magnus noted that it is still possible that lean women who exercise may have some other characteristic that prevents them from developing preeclampsia.

"Reducing weight is the best preventive measure, much better than being physically active, but then of course physically active is one way of losing weight," Magnus said.

SOURCE: American Journal of Epidemiology, October 15, 2008.