Yeh when I went for my second scan they said there is a big difference with what they can see between 19 and 20 weeks and to book closer to the 20 week mark. I went in at about 19 weeks 3 days and they were able to do all the diagnostic tests they needed as well as tell the sex of bubs too. It is amazing the detail they actually go into at this one. Looking at the chambers of the heart, measuring the parts of the brain etc. Good luck..maybe change your booking to a bit later. Better than having to pay twice
Mel