You have tri care prime? I see 3 different off post doctors and never have a co pay. Im at Fort Stewart and Currently am seeing the OB's on post, and a peri off post for my pregnancy, I will be giving birth off post, because my Peri is going to be my primary prenatal care giver from now on.
I know here, to go to the OB's on post you have to take a pregnancy test at the hospital, a positive test counts as a referral (I never had to see my Primary care doctor). Then you can just call the appointment line to make your first appt.
AND I dont know about where you are, but you probably will not get to have a "regular" OB at an army hospital (they have groups here, so you get like 10 doctors you randomly see). So you wont have your doctor deliver the baby, its just whoever is on call.