My brothers friend was told she was having a boy, bought everything blue and gave birth to a girl so it can happen, but its never happened to me, iv had 3 children already and found out the gender with all three and they got it right everytime, luckily you have a 20 week scan aswell to confirm for sure, with my 3rd i had a 16 week scan and was told girl i never beleived them (had two boys previously) i was too scared to buy pink, even though i had photos of her potty shot and i could see full well she was a girl, even when they told me girl at 20 weeks i didnt fully beleive it, first thing i checked when she was born was that she was infact a girl lol!!