Sex was on the 9th of june, the sonogram dates conception to the 18th , 19th. is this possible?

How far along?: What was the estimated gestational age when you had the ultrasound? If your first sono was late second trimester then a 9 or 10 day discrepancy could easily just reflect a fetus slightly smaller than average. Sex on the 9th could easily result in conception on the 13th or 14th. A latter sono could easily be off by 10 days. Lots of room for uncertainty!