I've always thought that arguing against this is the wrong approach to take. I think that life does begin at the moment of conception; honestly I can't think of any other point where it could be said to begin. It seems so obvious to me that I think the only reason the pro choice side has a problem acknowledging it is the implications that supposedly come from it.

I think the better approach is to say "yes it does but so what? It's a few hundred cells at that point so it's not a person with human rights". I think that the idea of life beginning at the moment of conception is only relevant if you think the embryo is being infused with a soul at that exact moment.