Ultrasound

Elizabeth
Does anybody know the earliest you can have an ultrasound that will show the baby? 
 I'm thinking it is 6 weeks but not sure. 
Have an appointment with my doc Thursday to let her know our awesome news and hoping she will organise an early ultrasound for us.  
I have my birthday off in about a week ( baby will be 5wks 3 days) and so does the husband so would be cool to have it as a pressie :)