Differences between a CNM and an OB-GYN

Hello all, I need some help. I have to do a presentation for one of my classes on CNM, and one of the topics I have to cover is the differences in practice between a CNM and an OB-GYN. The info must come from a professional nursing or goverment website. I know this should be easy, but for some reason I am having difficulty locating what I need. If someone can help point me in the right direction, I would really appreciate it. Thanks!