Pregnancy is an ideal time for lifestyle modifications, including increasing physical activity and eating a more healthy diet. Sedentary lifestyle and excessive gestational weight gain are major contributing factors to the obesity epidemic.
Exercise during pregnancy can maintain or improve fitness [1-3]. In addition, exercise may improve some pregnancy outcomes (table 1), including reduction in risk of developing gestational diabetes or preeclampsia, and reduction in macrosomia [4-6], but evidence is insufficient to infer significant risks or benefits for the average mother or baby .
In 2009, the American College of Obstetricians and Gynecologists (ACOG) reaffirmed the 2002 ACOG guidelines  for exercise during pregnancy and the postpartum period. These guidelines mirror the 2008 US Department of Health and Human Services Physical Activity Guidelines for all Americans , which have been adopted by the American College of Sports Medicine (ACSM) and the Centers for Disease Control and Prevention (CDC). (See "Overview of the benefits and risks of exercise", section on 'Exercise prescription'.) The ACOG guidelines recommend that, in the absence of either medical or obstetric complications, pregnant women exercise at a moderate level for 30 minutes or more per day on most, if not all, days of the week. Because the safety of a vigorous level of aerobic activity during pregnancy has not been studied sufficiently, vigorous exercise is not recommended during pregnancy. However, in the absence of medical or obstetrical complications, fit pregnant women may engage in more strenuous activities under proper supervision.
It should be noted that some types of physical activity can be less safe for pregnant women because of the anatomical and physiological changes associated with pregnancy and the additional risk of pregnancy-related complications. For example, changes in center of gravity during pregnancy may increase the risk of falling in sports that require good balance, and abdominal trauma from a fall is a risk factor for abruptio placentae.
Recommendations for exercise during pregnancy and the puerperium will be reviewed here. Physiological issues of exercise during pregnancy and the puerperium are discussed separately. (See "Anatomical and physiological changes of pregnancy and exercise" and "Overview of the benefits and risks of exercise".)