I had my referal at about 8 weeks for my 12 week scan, and i'm not sure about where you live, but it takes a few weeks to get in for a scan cause it's so busy! My clinic actually told me that if a scan is to be done, it needs to be done between 11 and 13 weeks and preferably 12 weeks just incase the dating isn't exact (ovulated late etc.). I already have my scan booked for my 19 week scan.. BTW - i went private for scans and Doctors, and if i were you and you were going private - i would just ring a clinic you will be getting your scan at and book in and go to your doctor and get your referal for blood tests and scan... blood test has to be done 3 days before the scan, as they collate the bloods with the scan to tell if everything is A O.K!