I am going to a public hospital for my antenatal care with the midwives and to have my baby and am not/have not payed anything. Medicare also covers ultrasounds if you go to a place that bulk bills.. same as if seeing a local GP.
As long as its the "Public" system or they say they provide "Bulk Billing" then its all covered under Medicare and you dont have to pay a cent, just show them your Medicare Card.