The American Congress of Obstetricians and Gynecologists recommends that healthy pregnant women exercise for at least 30 minutes most days of the week to maintain overall health and well-being. Health organizations such as the American Pregnancy Association advocate yoga as a stress-relieving, body-friendly means of exercise during pregnancy. Most physical activities should be modified to accommodate the physical and physiological changes during gestation, and many traditional yoga poses are easily modified with props and blankets. However, certain poses should be avoided for the safety of the mother and fetus.

Inverted Poses

Inverted poses such as headstands, handstands and shoulder stands, which place the head below the heart, should be avoided during pregnancy. This positioning creates reduced blood circulation to the uterus and developing fetus. Practicing inversions can sometimes cause dizziness or fainting in the general population, and because pregnant women tend to experience lower blood pressure, this illustrates another reason to avoid these poses.

Back Bends

Because back-bending poses such as upward-facing-bow or upward-facing-dog are designed to stretch and expand the abdomen, these should be eliminated from a pregnant woman’s yoga repertoire if practiced without modification. These poses compress the abdominal area and can overstretch and injure the muscles due to the effects of the hormone relaxin, which allows all of the body’s tissues to become hyper-mobile during pregnancy.

Prone Poses

In order to protect the developing fetus, women shouldn't practice poses that place them in a prone position on their bellies. Poses such as cobra, bow pose or locust--in which the majority of body weight is centered on the abdomen--should be avoided after the first trimester, or earlier if pregnant women feel any discomfort in the pose.

Supine Poses

In a review of literature related to exercise in pregnancy, Drs. Thomas Wang and Barbara Apgar note that any exercise executed in the supine position is contraindicated after the first trimester. This positioning is associated with decreased cardiac output in the mother, which in turn decreases blood flow to the fetus. Any poses traditionally practiced on the back, such as hand-to-big toe pose, or the resting pose shavasana, can be modified by rolling to the side.

Twists

Yoga poses that rotate the spine are calming and help to relieve back tension, which is a common complaint in pregnancy. However, any traditional twisting poses such as the seated Marychiasana or the standing rotating triangle pose that cause the spine to rotate extensively and compress the abdomen should not be practiced during pregnancy without modification.