With an experienced sonographer it's meant to be above 80% accurate

With DD2 my sonographer told DH that he was 80% certain of the gender and secretly told him. Hubby then had it confirmed (secretly still) at 16 and 19 week scan, lol. It was kept a secret from me, so when DD came out and hubby asked if I saw what it was I said "It's a boy!". The look on his face was priceless until I told him "just kidding. It's a girl" hahaha.