In general, aerobic, resistance, and flexibility exercises are safe during pregnancy . Walking, swimming, water aerobics, dancing, stationary biking, weight lifting, and stretching or yoga are some of the activities that are safe for pregnant women. However, each pregnancy, and each woman, is different. So, exercise programs are individualized to assure safety. Always ask your doctor for advice before beginning any exercise program when you are pregnant. Here are some of the precautions that you should follow.
Previously sedentary: The rule of thumb used to be that it was not a good time to start exercising if you were pregnant and had been previously sedentary. That stance has changed. The American College of Gynecology now states, "If you are active, pregnancy need not cause you to alter your fitness routine," and "If you have not been active, now is a good time to start." Of course, this doesn't mean throw caution to the wind and be reckless, but it does send the strong message that exercise during pregnancy is okay for most women.
Exercise while lying on your back: Excess abdominal weight can restrict blood flow to the fetus (particularly after the first trimester), and it can decrease cardiac output (the amount of blood the heart beats) by as much as 9%. Therefore, it's suggested that pregnant women avoid exercising while lying on their back, and particularly so after the first trimester.
Hydration: It's important to stay hydrated for exercise. Drink 8 ounces of water 20-30 minutes prior to exercise and 8 ounces every 20 minutes during exercise.
To summarize, exercise is safe, and even encouraged, during pregnancy, as long as the exercise is sensible and the above precautions are heeded. In fact, there are studies to suggest that exercise might even have a beneficial effect on pregnancy outcomes, including shorter labors, fewer abdominal deliveries, less discomfort during the pregnancy, and a decrease in perceived exertion during labor.