According to my dad (his wife is pregnant as well as me), when they went to have my brothers ultrasounds done they were classed as a PUBLIC Clinic - that is all Bell, MIA, Gribbles etc, however bloods and especially photogammitry has changed and is now classed as specialist items and therefore all clinic are now PRIVATE. This means they will bill you and you need to claim through medicare.
My bloods were $100 of which I got $40 back. However I have not paid for ANY ultrasounds so far. My next one will be at the RWH-Melb which is a public hospital and will not need to be paid for. My first two ultrasounds were referred to Healthscan Imaging which is a radiology place that was located within my Public, fully bulk billed (no appointment/walk in) medical centre and therefore I was bulk billed for those as well.

It may pay to look around for smaller radiology places when having your ultrasound.....

Also the bloods for the NT are billed as they are not done at a general lab. They are generally sent to a Childrens hospital or University where they are graphed and this is why they are billed.