No regular workout is "a waste of time" during pregnancy. You make your body stronger. I worked out 6 days a week with my second pregnancy, 24 hours after delivery, I took the baby for a stroller walk (the delivery time was only 15 minutes also). I found that my upper body toned much easier during lactation and pregnancy than my lower half. The body needs fat to make milk! I had been lactating way beyong nursing (a year and a half) because aerobic activities, wearing no bra in summer etc were keep on stimulating the milk production. During that time, my legs would not slim down. Now, finally after wrapping my breasts and doing absolutely no cardio workouts for two weeks, I don't lactate anymore and my legs are slimming down rapidly. To be fair, I haven't been overweight. Good luck!