How do midwives work?

Kayla • Nora Elyse 12/8/17 💕
I have thought about working with a midwife but I am unsure of how they affect my current ob/gyn "treatment". I really like my ob and would hate to not see her but I plan on going the more natural route (like no epihdural, but still deliver at a hospital) so I didn't know if I should see a midwife. 
Can I only use one or the other? Or do they kind of work in tantum with me throughout my pregnancy