Moderate exercise is one of the best things a mom-to-be can do for herself. It's well known that regular leisure-time physical activity during pregnancy reduces the risk of gestational diabetes and preeclampsia. But there may be one caveat. According to research on Danish women, strenuous exercise—especially intense, "jolting"-type activity—early in pregnancy may increase the risk of miscarriage.
The study of 92,000 women showed there was no increased risk of miscarriage from exercise performed after 18 weeks of gestation. Before 18 weeks, the risk was closely related to the amount and type of exercise. For example, women who swam during any phase of pregnancy showed almost no increased risk. But newly pregnant women who worked out intensely more than seven hours per week and performed high-impact activities, such as jogging and racquet sports, were 3.7 times more likely to have a miscarriage compared with similar women who didn't exercise.
Exercise during pregnancy deserves further study, says co-author Jorn Olsen, M.D., Ph.D., chairman of the department of epidemiology at the University of California, Los Angeles, School of Public Health. "We should make sure we base our recommendations on evidence, and that evidence is still too sparse," he says. For one thing, researchers don't yet know if the risk of miscarriage may be lower among women who were avid exercisers before becoming pregnant.
Until more studies are done, any woman who has had a previous miscarriage may wish to avoid high-impact exercise in early pregnancy, Olsen says.