Almost half of pregnant women in the United States exercise. Pregnancy exercise routines often have to be modified due to changes in balance, becoming more easily fatigued (due to increased blood volume), nausea or other discomforts, and weight gain. Regular exercise in healthy, well-nourished women is not only safe, but it may be beneficial. In fact, women who get regular, moderate exercise experience fewer of the normal discomforts of pregnancy and benefit from the sense of well-being regular exercise can bring. Women who consume a healthy diet, gain weight at the recommended level, and avoid activities that are too intense or may cause injury should not worry that exercise will harm their baby.

Pregnant women should exercise moderately, or at 50-60 percent of their maximum heart rate for 20 to 30 minutes three times per week. Brief periods of exercising at 70 percent of maximum heart rate is okay.

Research has demonstrated that women who exercise regularly before and during pregnancy return to their pre-pregnancy weight, strength, and flexibility levels faster than their sedentary counterparts. In general, there is a quicker recovery from pregnancy, labor, and childbirth (American College of Sports Medicine, 1995).

Exercise Guidelines During Pregnancy

The American College of Obstetricians and Gynecologists (ACOG) developed guidelines for exercise during pregnancy. These guidelines are for women who do not have additional risk factors for pregnancy complications. Of course each woman is different and should consult her physician to determine what is appropriate for her.

• During pregnancy, women can continue to exercise and derive health benefits even from mild-to-moderate exercise routines. Regular exercise (at least three times per week) is preferable to intermittent activity.
• After the first trimester, women should avoid exercise in the supine position (on the back). This position is associated with decreased cardiac output. Prolonged periods of motionless standing should also be avoided.
• Since oxygen availability is decreased during exercise, women should be encouraged to modify the intensity of exercise according to maternal symptoms. She should stop exercising when fatigued and not exercise to exhaustion. Weight-bearing exercises may be continued under many circumstances with some modifications. Non-weight bearing exercises such as swimming or cycling will help minimize the risk of injury and facilitate the continuation of exercise during pregnancy.
• Any exercise which involves a potential threat of abdominal trauma or loss of balance and risk to mother or infant should be avoided.
• Since pregnancy requires an additional 300 calories per day, exercising women should make sure they are eating adequately.
• Adequate hydration, appropriate clothing, and optimal environmental surroundings are extremely important for body temperature regulation during exercise.
• Many of the physical changes during pregnancy persist 4-6 weeks after delivery so pre-pregnancy exercise routines should be resumed gradually based on a woman's physical capability.

More General Exercise Recommendations

• If you have never exercised before pregnancy, start slowly and build up gradually. Individualized programs with lower-intensity exercise are recommended 
• If you were exercising before pregnancy, then the goal should be to maintain your current exercise program with a few adaptations
• Gaining weight is good
• Medical supervision is recommended when exercising. Avoid contact sports 
• Avoid exercise in which loss of balance could occur: rocky terrain, unstable ground 
• Avoid exercise in extremely hot weather
• Wear appropriate clothing
• Avoid high-intensity exercise
• Always warm up and cool down
• Communication with professionals is key
• Listen to your body

Sources: Judith Brown, R.D., M.P.H., Ph.D. , WebMD Medical Reference from "Nutrition & Pregnancy: A Guide from Preconception to Postdelivery"; American College of Obstetricians and Gynecologists. Technical Bulletin 1994:189; National Center on Physical Activity and Disability (NCPAD).