Actually we saw a midwife. She and the nurses has no idea what the sex was. Outside of one time, the gals that did the sonograms would avoid looking so they wouldn't accidentally tell us the sex. I had no idea what I was having, I just knew that I would love the crap out of the kid. It was an amazing experience to be the one to announce to the room that it was a boy (I was expecting a girl the entire pregnancy and probably owe the kid some therapy sessions).
I have nothing against finding our early. We might do it on child #2 to avoid any unintentional negative emotions my wife might have after labor if we have a 2nd boy (this is a real thing by the way).