Check with your doctor if you've never exercised, and follow these safety guidelines for exercising during pregnancy.

Wait 1 to 2 hours after eating to exercise.
Drink one or two 8-ounce glasses of water before you start to exercise.
Don't do exercises that involve jumping, twisting, or strenuous activity.
Keep your heart rate below 140 beats a minute.
Don't become overheated.
After the fourth month of pregnancy, avoid exercises in which you lie flat on your back.
If you always or nearly always feel tired for more than 2 hours after exercise, see your doctor.