Guidelines for Exercise During Pregnancy Overdue

A commentary highlighting the most current exercise guidelines in pregnancy for obstetricians and gynecologists, as well as subsequent research, touts the benefits of exercise during pregnancy, including vigorous aerobic activity, greater energy expenditure, and strength training, with certain safety limitations.

Gerald S. Zavorsky, PhD, director of the Human Physiology Laboratory at Marywood University in Scranton, Pennsylvania, and Lawrence D. Longo, MD, from the Center for Perinatal Biology at the Loma Linda University School of Medicine in California,suggest key updates for existing guidelines in the June issue of Obstetrics & Gynecology.

According to the summary, the initial Centers for Disease Control and Prevention and American College of Sports Medicine recommendations were established about15 years ago, and it has been 9 years since their adoption by the American College of Obstetricians and Gynecologists.

“Since then, new science has emerged that has enhanced our understanding of the amount of physical-activity expenditure needed and the intensity of exercise needed to improve health outcomes and quality of life,” the authors note.

Specifically, the safety guidelines during pregnancy suggested by the authors are as follows: with respect to muscle strengthening, in pregnant adults aged 18 to 45 years of age: “8 to 10 muscular strength exercises can be performed for one to two sessions per week on nonconsecutive days. One aerobic training session can be replaced by a muscle strengthening session in the weight room or at home,” they suggest.

The authors also recommend using lighter weights with more repetitions. “Heavy weights may overload joints already loosened by increased levels of the hormone relaxin during pregnancy,” they note.

Walking lunges, which may raise the risk for injury to pelvic connective tissue, and free weights, which may hit the abdomen when used, should be avoided. Instead, the authors recommend the use of resistance bands.

In addition, lifting while flat on one’s back, in the second and third trimesters, may cause the uterus to compress the inferior vena cava, into which blood from the pregnant uterus flows. “This increased pressure can be transmitted to the placenta and could compromise fetal blood flow in the gas-exchange area, thereby limiting oxygen supply to the fetus.” Instead, these movements can be performed at an incline.

The Valsalva maneuver, that is, forcefully exhaling without releasing air, can rapidly increase blood pressure and intra-abdominal pressure and also may decrease oxygen flow to the fetus. Rarely, the Valsalva maneuver may result in a decrease in blood pressure.

Dr. Zavorsky and Dr. Longo recommend that pregnant women who exercise should listen to their bodies and pay attention to what is going on physically. “If you feel muscle strain or excessive fatigue, modify the moves and reduce the frequency of the workouts,” they suggest. “Pregnancy is not the time to perform heavy weightlifting, but muscle strengthening according to these guidelines will burn calories and increase the resting metabolic rate.”

The researchers summarize their guidelines by stating that “increasing weekly physical-activity expenditure while incorporating vigorous exercise provides optimal health outcomes for pregnant women and their fetuses…. [l]ight strength training during the second and third trimesters does not negatively affect newborn body size and overall health.”