My NHS 20 week scan there where able to give me a answer, so might be best to be for sure and wait until 20 weeks ish, if you are paying for a private one. We where lucky as baby was in a good place that they could get a clear view that it was a girl.
I wonder if some hospitals have got it wrong and people have maybe tried to claim against them, so make it their policy not to do it. I know a friend had a boy as her first and was told it was a girl the second baby. So all the blue stuff was given away and pink things brought. Little shocked when a boy arrived. OOOPPPPSSSS. May i just add they are not the sort of people that claimed, but i guess there are some out there that do.