Expectingfitness.com is a website that addresses exercise and pregnancy issues. The very basic rules are that exercise in moderation is good, your heart rate should not exceed 140 beats per minute, don't get too hot, and drink lots of water. You should stop if you feel faint or light-headed. Of course, check with your health care provider. Don't do activities where you or your abdomen are at risk of being injured (kick-boxing, etc.)