I was 41 when I was carrying my first baby, I skipped the Oscar test but my Dr checked did the Nucal Scan anyway ( like a normal ultrasond scan) it was low risk. I went ahead with the Amniocentesis as I read in this article the risks of miscarriage could be as low as 0.1%. And I trust my Dr will do a good job.
The 0.5 - 1 % rate are old figures, according to here: http://www.medicalnewstoday.com/articles/55680.php
The results came back as normal, although I was worried.
If you want 100% accuracy, only CVS and Amniocentesis can tell you that.