A lot will depend on your instructor. Early in my pregnancy I had a fantastic yoga teacher who was great at 'body work' so I got a lot of stretching and relaxation. Unfortunately she had to quit teaching. Late in my pregnancy I went to Pure Yoga. The instructor was very into breathing, which I didn't have a lot of patience for. She did teach us some positions which were good for relieving lower back ache, improving circulation and dealing with swelling feet. I did get a bit bored with all the breathing though and wanted my previous teach back! Overall, if the yoga teacher is qualified to teach pregnant mums, yoga is a good thing to do, for stretching and suppleness esp when you have a big tummy and balance is a bit off. I swam a lot too, almost daily towards the end of my pregnancy, and this was really the best thing.