Exercising Through Your Pregnancy, by James Clapp, MD. This is a must have book if you exercise prior to pregnancy and want to keep up your efforts. A book to take to your OBGYN, cause some of those guys are still on the bandwagon of “don’t let your heart rate go above 140!”.
Here is the Amazon Link. http://www.amazon.com/Exercising-Through-Pregnancy-James-Clapp/dp/1886039593
Lots of good scientific evidence about continuing to exercise, and starting to exercise while pregnant.