Is It Safe to Exercise During Pregnancy?

Women who want to maintain a high exercise level during pregnancy may be frustrated at the outdated ("keep your heart rate below 140") and vague ("stop exercising if you feel tired") information they find. "Physicians aren't trained to counsel pregnant women about exercise," says James Pivarnik, PhD, vice president of the American College of Sports Medicine. "It's a rare bird who keeps up with the exercise and pregnancy literature." Doctors may have you believe that we know little about how exercise affects pregnant women. But in reality, we know quite a bit -- and it's good news for runners, cyclists, and gym rats who are moms-to-be. "If a woman is having a normal pregnancy, she can continue to exercise, and the upper limit of the level can be reasonably close to what she was doing before pregnancy," Pivarnik says.

Will Exercise Harm My Baby?

Pregnancy Workouts: Is It Safe to Exercise?
Pregnancy Workouts: Is It Safe to Exercise?
pregnant woman holding exercise ball


The first thing that most newly pregnant exercisers worry about is miscarriage -- thanks to age-old myths that have women believe that a bout of strenuous exercise can harm the baby. "There is no real evidence that exercise is linked to miscarriage," says Bruce K. Young, MD, coauthor of Miscarriage, Medicine & Miracles (Bantam) and professor of obstetrics and gynecology at New York University School of Medicine. Heavy exercise isn't going to hurt your baby, but it will tire you more quickly than it did prepregnancy. The amount of blood a woman has increases during pregnancy by about 50 percent, and her heart needs to work harder to push all that blood around -- including circulating it through the placenta, an extra organ. "That means the stress on your heart will be 50 percent greater for the same exercise that you were doing before pregnancy," Dr. Young says. So you can work just as hard doing less than you did before you were pregnant.

Pregnancy isn't the time to push yourself to the max, but it's also okay -- and good for you -- to get your heart rate up with cardiovascular exercise. Although a target heart rate of 140 is a number that's often cited, there's no precise number to shoot for. When prenatal trainer Erinn Mikeska, owner of Delivering Fitness, in Dallas, works with pregnant women, she has them monitor their rate of perceived exertion (RPE) -- how hard they feel they're working, on a scale from 1 to 10. "You probably want to stay around 5 or 6," she says. In the first trimester, when you're not any bigger and don't yet have balance issues, you may be able to exert yourself more if you're not too tired.

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