Most pregnant women can and should participate in regular physical activity, according to the latest advice from sports medicine experts.

A review of research on the topic suggests that exercise is beneficial for pregnant women - including those who were previously inactive - and that it poses little or no harm to the developing fetus.

“Physicians who see pregnant patients should be able to discuss exercise recommendations based on each woman’s prepregnancy activity level, general health, and fitness goals,” writes Dr. Amanda K. Weiss Kelly, of Case Western Reserve University, in Ohio.

“Unless contraindications are a factor, moderate aerobic and strength-conditioning exercises should be encouraged,” she adds in the June issue of The Physician and Sportsmedicine.

Years ago, most women were advised to refrain from exercising during pregnancy for various reasons, including the observation that women whose occupations required physical work or standing for long periods of time tended to experience pre-term delivery and to have babies who were small for their gestational age.

Also, published reports have suggested that pregnant women who exercise may experience certain physiological and metabolic changes, such as increased temperature and decreased blood flow to the uterus, that could hinder fetal development.

Overall, however, research shows that exercise poses virtually no risk to the fetus. Conflicting evidence exists for its effect on fetal size, but most studies suggest that exercise does not increase or decrease the weight of infants. Further, babies born to exercising women may be less likely to have abnormal heart rate patterns, and appear to be more alert than those born to sedentary mothers.

Exercise is also very beneficial for expectant mothers, and does not appear to be associated with a higher risk of preterm labor or delivery, as previously believed.

Low-back pain and other musculoskeletal complaints tend to be less common among women who exercise while pregnant in comparison to their sedentary peers. Pregnant women who exercise tend to have a better self-image, less signs of depression, and they have been shown to return to their pre-pregnancy weights more quickly than sedentary women.

Further, the American Diabetes Association supports the use of exercise during pregnancy, as it has been linked to the prevention and treatment of Gestational diabetes, Kelly notes.

Yet, not every exercise is suitable for pregnant women, and not all pregnant women should participate in an exercise program.

Exercises that require women to stand or remain motionless for extended periods of time, for example, should be avoided because of their potential affect on the heart and their association with low blood pressure. Further, women with Heart disease or certain types of lung disease should not exercise during pregnancy and those with chronic high blood pressure, Thyroid disease and other significant conditions should be evaluated before they begin to exercise.

The current guidelines are not just for women who are already physically active, however. Research shows that sedentary women can also safely begin exercising while pregnant, although many wait until the nausea and fatigue of their first trimester has passed.

To avoid injury, these previous non-exercisers are advised to start exercising for 15 minutes three days a week and gradually increase the exercise intensity and time, to a half hour on four days a week.

Women who are already active can continue with their regular regimen, adjusting their activity to optimize their level of physical comfort. Those involved in competitive athletics, however, may need to reduce their level of activity, or even discontinue some activities while pregnant.

Overall, pregnant women, like all women, should pay attention to their bodies and modify the intensity of their activity according to their symptoms, Kelly’s report indicates. They should not over exert themselves and should stop or reduce their level of exercise if they are too short of breath to engage in conversation.

Pregnant women should also stop exercising and consult with a physician if they experience vaginal bleeding, severe shortness of breath, headache, chest pain, leakage of amniotic fluid or if they notice a decrease in fetal movements while exercising, experts say.

SOURCE: The Physician and Sportsmedicine, June 2005.