I used to work at an OBGYN office and fat mothers were abundant. You don't need to run miles every day when you're pregnant, but the OB always recommended light exercises like yoga or 30-min walks for an easier pregnancy and delivery. You shouldn't be out of breath walking in from the door to the sign-in desk 5 feet away. I have a serious disdain for pregnafatties. Their urine always had signs of protein or excess sugar or some other anomaly that would need to be checked out more thoroughly.