When is the earliest you can find out the sex via ultrasound?

I'm 12w 3d, but due to a Subchorionic Hematoma I am getting my third ultrasound next week. I don't know the date yet but I will be either 13 weeks or 14. What are the chances of me finding out the sex of the baby? Has anyone found out that early? Just can't wait to find out!! :)