Aparrently the blood test is best done at 10 weeks and the u/s between 12 and 13 weeks. It was a bit annoying going back twice in two weeks to the OB but worth it as I got to see bubby on the u/s twice.
I've been trying to find the leaflet around here to share the info with you but I can't find it :-k
My results came back as 1:25000 risk of downs syndrome. They will still check for other markers at the 19wk scan but those odds are very good that all is clear. The fluid measurement was 1mm.