I think my letter took about 2-3 weeks to come back with the combined test results, but they said they would phone me within a week of taking the bloods, if anything was looking unusual.
(I had a previous triploidy/molar pregnancy in 2009)
I had my bloods done the same day I had the NT scan though, so it might be different for you. Maybe you will get the results at your next MW appt? xx