Are you starting to itch for some postpregnancy exercise -- other than lifting baby? It's best to wait at least six weeks after delivery or until your doctor gives you the go-ahead before you resume or begin a vigorous fitness program. This gives the uterus enough time to return to its normal size and gives you a chance to get a sense of routine with your new baby. But there are no hard-and-fast rules about when and how much to exercise. It depends largely on how fit you were before and during your pregnancy, the nature of your delivery (you'll need to wait for your incision to heal if you had a cesarean), and how much rest you get once baby arrives.