I'm so very sorry you had an abnormal screen and I know "statistically" that things are more than likely to be fine for you. On the other hand, for my own sanity, I have to have to have the amnio and know for sure, rather than rely on statistics for a test that I now know I should probably not have been offered.
I was very much aware of the false postive and negative rates with this test in the general population before I had it, but not that the Quad test is essentially meaningless in IVF pregnancies due to there not being accurate reference levels for HCG in IVF pregnancies. You were lucky to have at least had some counselling.
I can certainly understand you reasons for not having the amnio and in that respect you are much braver than I am. I wish you the very best with it all.