I am very sorry to hear you are going through this. This pregnancy we also had ver low Papp-a, but ours was a bit higher than yours at about 0.25. Our HCG was also abnormal in the sense it was 2x the average. As a result we were given a 1:59 chance of DS. We chose to have an amino at 18 weeks (which I honestly imagined would be much worse than it was) and we were given the all clear 1 day later. I understand that it is a very stressful and depressing time. Take care and I hope that you get good results. Please let us know how you go. Like you said, the odds are heavily in your favour, so I hope you get some good news soon.