Several versions of exercise guidelines for pregnancy have been published, the latest 9 years ago. These guidelines recommend 30 minutes or more of moderate exercise on most if not all days of the week for pregnant women in the absence of medical or obstetric complications. However, moderate-intensity exercise was not defined. In addition, the specific weekly energy expenditure of physical activity was not suggested. Recent research has determined that, compared with less vigorous activities, exercise intensity that reaches at least 60% of the heart rate reserve during pregnancy while gradually increasing physical-activity energy expenditure reduces the risk of gestational diabetes. To achieve the minimum expenditure of 16 metabolic equivalent task-h/wk, one could walk at 2 miles/h for 6.4 h/wk (2.5 metabolic equivalent task-hours, light intensity) or, preferably, exercise on a stationary bicycle for 2.7 h/wk (6 to 7 metabolic equivalent task-hours, vigorous intensity). To achieve the target expenditure of 28 metabolic equivalent task-hours per week, one could walk at 2.0 miles/h for 11.2 h/wk (2.5 metabolic equivalent task-hours, light intensity) or, preferably, exercise on a stationary bicycle for 4.7 h/wk (6 to 7 metabolic equivalent task-hours, vigorous intensity). The more vigorous the exercise, the less total exercise time is required. Light muscle strengthening performed during the second and third trimesters of pregnancy has minimal effect on newborn body size and overall health. On the basis of this and other information, updated recommendations for exercise in pregnancy are suggested.