Ask Well: Is It Safe to Exercise During Pregnancy?

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The recommendation to limit heart rate to 140 during pregnancy was made in 1985, at a time when “the scientific data on strenuous exercise in pregnancy was very scarce,” said Dr. Raul Artal, the obstetrician and exercise physiologist who developed the guideline for the American College of Obstetricians and Gynecologists (ACOG). But the recommendation was later withdrawn. “It has no scientific value,” Dr. Artal said

At the time, though, the recommendation marked a sea change in medical advice, because it condoned physical activity during pregnancy for the first time, Dr. Artal said. Until then, women were treated as though they had an illness when they were pregnant, and they were advised to relax, avoid strenuous exertion and even bending or stretching, for fear they would strangle or squash the baby.

“Textbooks, until the late 1960s and early '70s, said pregnancy is not a good time to exercise,” Dr. Artal said. “They said, ‘It’s O.K. to walk.’ ’’

Attitudes have since changed significantly. ACOG now encourages pregnant women to engage in moderate-intensity exercise for at least 20 to 30 minutes a day most days of the week, as long as there are no medical or obstetric complications.

Research has shown that physical activity during pregnancy has benefits beyond maintaining or improving physical fitness, including helping with weight management, reducing the risk of gestational diabetes and preeclampsia, making it easier to cope with labor pain and easing recovery from childbirth, said Dr. Artal, the main author of updated guidelines issued late in 2015.

Although an upper level of safe exercise intensity has not been established, the new recommendation says that women who exercised regularly before pregnancy and have no pregnancy-related complications “should be able to engage in high-intensity exercise programs, such as jogging and aerobics, with no adverse effects.”

Some modification of exercise routines may be necessary to accommodate physiologic and anatomic changes that occur during pregnancy, such as changes in the center of gravity, laxity of joints and ligaments and respiratory changes. Activities that involve a high risk of falling, such as downhill skiing and horseback riding, should be avoided, as should contact sports, scuba diving, skydiving and hot yoga.