With my DD at the 19 weeks scan it showed an echogenic focus in the left ventrical. Also found to have only a 2 vessel cord, not 3 vessels. So that was 2 markers for Down's. So i had a follow up scan with a specialist at 21 weeks. After, i had a 1:2900 chance of her having Down's, which for my age at the time(18) was quite high risk. But decided not to have an amniocentisis. DD is now a perfectly healthy 20 month old. So for us, it wasn't an indicator that she had it. Apparntly about 4% of fetus' have this and go on to be a healthy baby.