Regular, moderate exercise does not significantly affect length of gestation or birth weight, and it may ease pregnancy and labor. Active pregnant women should maintain adequate hydration and nutrition, avoid hyperthermia, and take precautions if obstetric or medical complications are present. Supine exercise, contact sports, high-altitude exertion, and scuba diving should be avoided, and some women, including those who lift weights or do high-impact exercise, may need to modify their routines. Most women can begin or continue to exercise during pregnancy.