NP, PA, MD, or DO?

My fiancée wants to go into obstetrics, but we're have issues determining what the best path to that may be. I was wondering if people could speak to the differences between the actual practice of NPs, PAs, and MDs/DOs in the field. We would also love any help in the cost/benefit analysis in terms of debt, salary, malpractice, etc, and years to completion and so forth. There's a lot of differing information on the web, and we're just not sure where to start. Thank you!!!
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums