I don't know of any OB/GYN specific books. I think it's great that you are educating yourself prior to going back in though. It shows great initiative. We had a girl once come in for an interview and she had researched us on the web and knew a little about what we do, etc. It impressed us. I would just review the cpt codes for OB/GYN, maybe google a couple things, then you can at least say that you had researched a little. Good luck with the interview.
Michele