Not sure, really! For those cases I always say it 99,9%, leaving that 1% for some unexpected event. I don't have my personal experience yet. I'm just waiting for the 12 wks scan after successful donor egg ivf cycle. But as far as I remember, my niece had this ''confusion'' but don't remember the exact term. Her baby used to hide itself for long, so they didn't know the gender for a couple of months. Then dr managed to ''catch'' him once turning quickly inside and told she was more to think it was a girl. But then it turned out it was a boy! Dr explained this is happens sometimes. The genitalia may develop a bit differently which causes all those confusions on the early stages. Hope your LO will show the best=) Wishing you the best.