Gender change?

Kimberly • I'm 34. I have 4 children; 3 boys and 1 girl.
I had my last appt at 16 weeks (currently 18 weeks) and the doc "best guessed" boy. There was a ton of cord between the legs and he had to work to get a shot of the gender. I go back January 4th for the level 2 anatomy u/s. Has anyone been told "boy" at 16 weeks and the gender was really "girl" at the 20 week anatomy u/s?