OK so you get a referral to an Ob of your choice.
You go and see them. You pay for all visits and any scans and bloodtests. You can claim this at medicare but not from your PHI.
You usually get charged a management fee at the halfway point, this isn't (I'm pretty sure - my Ob didn't have one) claimable either. After the birth they then charge you depending on the type of birth you had. If you use an aneasthetist, his bill will be separate. The hospital stuff is claimable with your PHI.

They will refer you to the hossy they work at.

When labour starts you ring them and go in....you don't generally meet any midwives before that point.