Hi
there is no definate answer some people do, I did with one of my pregnancies at 6w5d however it depends on implantation times. Good luck with the ultrasound
Like lizzy said some woman go in at 5-6 weeks for there first u/s and they cant find a heartbeat which is really common that early. like lizzy said before if you ovulated later then the average time and it implanted later they might now be able to find one. a few days can make a huge difference on whether it is visible or not. So if you go in and they can't find one, they usually don't assume its an m/c or anything bad, they will usually schedule for another in a week or so.