well i had a sexing scan and 4d scan at the same appointment, i was 21 weeks and we went private for it although the sexing scan was black and white then after she done that she gave us a 4d for 20 min, it did cost £140 for both but so worth it, i wanted to have it done at 17 weeks but she told me to wait until 20 when it is much more accurate, the cool thing was that a week afetr we went for the private scan i had my nhs anomaly scan and had it confimed again that im carrying a girl, i feel better that iv had it confirmed twice, less chance of them being wrong...lol