I had my blood done on a Tuesday and the scan the following Wednesday (8 days later). My scan ended up being done when I was 12wk+5 as the dating scan was a few days off apparently.

My Dr said that it really didn't matter if I had the blood taken before or at the same time as the scan but if I wanted the results quicker ie 30mins after scan, get the bloodwork done a few days beforehand.

HTH!