Fitness Q&A by Richard Weil
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.
Heart rate: Pregnant women used to be told not to raise their heart rate higher than 140 beats per minute during exercise. However, that recommendation was based on limited evidence, and the American College of Gynecology no longer makes a recommendation for heart rate during exercise. What is known from research is that exercising at approximately 70% of maximal heart rate causes no change in fetal heart rate. The Canadian Society for Exercise Physiology and Society of Obstetricians and Gynecologists of Canada recommends the following heart rates based on age for pregnant women:
It is best to speak with your doctor about heart rate limitations for exercise.
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.
Balance: Center of gravity shifts as pregnancy progresses and creates balance problems. Therefore, activities that increase the risk of falling, like vigorous racket sports, skating, and gymnastics, should be avoided.
Contact sports: Sports like field hockey, boxing, and soccer, where there is a risk of body contact or being struck by a ball or other object, should be avoided.
Heat: Muscles produce heat during exercise, which raises core body temperature. The increase in core temperature creates a theoretical risk of harm to the fetus, particularly in the first trimester. The body protects against this by lowering body temperature throughout the pregnancy, however, it would be prudent not to exercise in extreme heat or humidity when you are pregnant. The American Academy of Family Physicians recommends (1) exercising in the early morning or late evening to help you avoid getting too hot and (2) making sure a room has enough ventilation while exercising indoors and to use a fan to help you stay cool.
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. I recommend that you speak with your doctor before starting to exercise, and if you already exercise, check with your doctor about how to continue through to your delivery. I also recommend the book Exercising Through Your Pregnancy by James Clapp, MD, as an excellent resource. Enjoy your workouts!