There are differences between a CPM, a CNM, and an OB-GYN. Those differences include the education required, the philosophy of practice, and the clients we each serve. I know I'm not trained, or equipped to handle the situations an OB-GYN does, and the same goes for CNMs. I value the skills and education they have, and am thankful they are able to help clients when they need more than I can offer. Each provider has their own skill set, and is best suited to serve particular needs.
OB-GYNs are absolutely the experts to go to when a mother has conditions or indications of a condition that puts her life or baby's life at risk. A mother who is a smoker, who has high blood pressure, who has a history of blood clotting issues; a baby who is not growing, whose ultrasound shows a possible congenital issue, who isn't tolerating labor well will benefit from the care an OB-GYN can provide. A mother who wants the care of a midwife as well as the options a hospital has such as an epidural will benefit from the care of a CNM. For the mother who is healthy, and having a low risk pregnancy that wants to have baby in the comfort and security of her home, a CPM has the skills and training to support her well. Each type of provider has a niche, or particular women they would serve well.
There are differences in skills, training and expertise among types of providers. Since I support births at home, that is what my training emphasized. That is why I was required to attend at least 55 births (I attended a lot more), with 45 of those in the home setting. OB-GYNs and CNMs are not required to attend any home births but they do have to attend hospital births as part of their training since they will be working in the hospital. With the differences in training and skills, if all the providers can work together when different skills are needed, both babies and mothers will benefit from the wide range of expertise.
To refer to me as "just a CPM" is belittling, in the same way as saying "she's just a stay at home mom". It implies that there is less value in being a CPM instead of recognizing that each type of provider has unique skills and understanding that makes them valuable in their own right.