Congratulations on making a wonderful choice for your health and your baby's health. Women who continue to exercise in pregnancy have higher self-esteem, a more positive attitude about pregnancy and easier labors. Some guidelines are important, however.

• Moderation is key! Now is not the time to increase your mileage or take up a new sport. Pregnancy increases the demands on your heart and lungs. If you are a serious athlete, you'll need to cut back the intensity of your workouts halfway through pregnancy (20 weeks from your due date).
• Pregnancy loosens your joints in preparation for giving birth. You become more flexible but also more prone to sprains and strains. Be sure to warm up well before exercise. If you lift weights, cut back the weight and increase the repetitions. And never, ever hold your breath while lifting weights or grunt to help you lift more. Always exhale slowly when lifting weight.
• The weight of the baby becomes an important factor around 20 weeks. Your balance is off. Sports requiring sudden movement or balance should be stopped by then. Even bicycle riding becomes dangerous in traffic, where a fall could be very serious. Consider changing to a stationary bike at this time, if you like bicycling.
• Don't get overheated. Raising your body temperature is dangerous for you and Baby. Exercise doesn't actually increase your body temperature significantly, but your environment does. During the summer, try to exercise before 8 a.m. or after 6 p.m. Also, humidity makes it hard for your body to get rid of heat. This is why hot tubs are a bad idea, too — they raise your temperature very rapidly without your realizing it. If the temperature and the humidity are higher than 80 degrees, exercise indoors or in a swimming pool. If you can't afford a health club, go to the mall and start walking!
• Be sure to drink lots of water – before, during and after exercise. If you get thirsty, it's too late – you're already dehydrated! Your blood volume is greater during pregnancy, and you need more fluid to keep it up. Try to drink a pint of water before exercise and a cup every 20 minutes. Sweating can cause you to lose 1 to 2 quarts of water per hour!
• Contact sports should be stopped after 12 weeks. At this time, the uterus begins to rise above the pelvic bones, and your baby could be injured by a blow to the belly.
• Stop exercising and call your doctor if you have any of these symptoms: pain, dizziness, shortness of breath, faintness, vaginal bleeding, rapid heartbeat while resting, difficulty walking, contractions or the baby isn't moving.
• Don't exercise if you have pregnancy-induced high blood pressure, ruptured membranes, preterm labor, incompetent cervix, cerclage, vaginal bleeding after 12 weeks or fetal growth retardation (baby growing too slowly).

Want to see more?

• ACOG Pregnancy Exercise Guidelines
• Yoga: An Ancient Practice for Pregnancy in the Modern World
• Belly, Back and Bottom: Your Postpartum Recovery Plan
• Battle of the Bulge: Returning to Your Pre-Pregnancy Weight
• Talk About It