Try not to worry, my risk factor for Down's syndrome came back the next day as 1:650, which is more down to age than anything (I'm 33). My fold measurement was also 2.3mm but that is normal so I'm not worried about that. Have been offered the harmony test to know for sure but I wouldn't change anything even if the baby did have downs. Try not to stress about things, it will only make you feel worse. That measurement is normal for your babies size and each pregnancy is different so try not to compare with any other x