Just because the measurement is "good" doesn't mean no DS. The measurements are important yes, but the reason the nuchal scan is done IN CONJUNCTION with blood, is to get a more accurate picture for DS and trisomies 13 and 18. Not to scare you or anyone but I just went through this and had been so excited for a good measurement, but then my blood came back high risk. A DS baby CAN have a "good" nuchal measurement.
Do many women of AMA receive false positives for their nuchal scan? Yes. It's NOT a dignostic test, it just exists to tell you odds and so that if your odds are HIGH you can make a choice as to how you would like to proceed with additional testing (or not)
I just want people to be informed of this in case they think "oh my measurement was good, I don't have to worry" You need to get the measurement AND blood, see what the two combined tell you and then decide if you want either to leave it all alone and not do anything, or go on to have a CVS, Amnio or MaterniT21.
I know I have gone on and on about this...I will shut up from now on