Yoga has quickly become one of the most popular exercises for pregnant women, and it's little wonder! Yoga is an ancient discipline that has a physical aspect which is great for enhancing muscle tone and improving balance. The physical practice can help you learn to breathe deeply and relax-vital skills during the labor and delivery to come! If this sounds good and you're ready to try yoga, make sure that your instructor knows you're pregnant. Or, even better, join a class designed specifically for expectant mothers. During your first trimester, there are few pregnancy-imposed restrictions on your yoga routine, as long as you are aware of your body. In later trimesters, however, your joints will be looser and you'll want to take more care with twisting and inversion poses. Also avoid any positions that require you to lie flat on your back, which will put pressure on the vein that returns blood from the legs to the heart. This can cause dizziness and shortness of breath. You should also avoid Birkram yoga, or hot yoga, which takes place in a room heated above 90 degrees Fahrenheit and can cause your body temperature to rise to unsafe levels. As with any exercise program, be smart and talk to your doctor before beginning a yoga routine.