Yoga can allow for a more comfortable pregnancy and women who practice yoga while pregnant are more likely to experience optimal health in the pregnancy and a more positive experience of birth and the post-natal period. It is important, however, for a woman to listen to her body and respect the cues given by her body at any given time. Overall, Yoga is an effective way to reduce stress and maintain fitness and flexibility throughout a pregnancy and beyond.
If you are not a regular yoga practitioner prior to becoming pregnant, while pregnant is not the best time to begin. Why, because you are unfamiliar with yoga and have not given your body the opportunity to adjust to the practice of yoga, the stretches, the bends, the positions, etc.