If it helps any, with DS I had a scan at 9 weeks, just to make sure everything was going ok and to hear the heartbeat - and a GP referred me to the scanning place for that. Then I had the 18-20 week scan referred by my OB.

With this pregnancy, I heard the heartbeat at 8 weeks in my OB's rooms (cos she has a really old ultrasound machine) and didn't have a 12 week scan (I don't think she refers you to them unless there is a problem?) and have only had my 18-20 week scan, and that is all I get unless I specifically ask for a 3D one.

Hope this helps !!