I was told to carry on with normal exercise regime.......within reason but dont suddenly up your exercise. You just have to be careful of overheating in 1st trimester so watch that and drink plenty of water. Second trimester is when you need to modify things like ab exercises and some other things. My aerobics instructors are great and give me alternative exercises throughout my pregnancy depending on what they are doing in class on that day!! Talk to your obstetrician if you've got any concerns. Be prepared for all the idiots that frown at you and tell you you shouldn't be exercising while pregnant. It drives me nuts at the gym. So I should follow their advice and not my obstetricians?? Hehe