I am having my 19 week scan in three days can someone tell me what to expect at it? They lady on the phone said it will take an "Hour" is that true?

I have never found out any of the sexes with any of the other kids so have no idea what to ask about that. Do I have to ask or do they offer for me to know the babys sex? And are there certian places that will not let you know. I am having myn done at a local medical center!I am too scared to ask incase she is rude and says we dont allow that here!

What else should I expedct to happen at that scan!

Sorry just a litte nervous cause its been a while!