If you have been doing regular exercise before pg then you are ok to continue it, just listen to your body and don't push hard when it's telling you to pull back a bit. However, if you were not into regular exercise, now is not the time to go on a fitness campaign Stick to low impact, low intensity stuff like walking and swimming rather than marathon running or weight lifting and you will be fine. I'm sure fitball & pilates are fine, just make sure your instructor knows you're up the duff and can change any exercises if needed.