J.H.
I loved doing yoga when i was pregnant. Then again, I loved doing yoga when I wasn't pregnant.
I think doing yoga helped me relax through out the pregnancy, and when I was in labor, I was able to center myself, breath through contractions. Was it all because of the yoga? Probably not. Did the yoga help though? Probably.
I say if you're used to doing it, keep doing it. If you've never done it before and you're interested, then try it. If you want to do it only because you think it might help with labor, then it's probably not worth it.