My test results came back with a very high ratio (1:30 i believe) at risk for DS (it was a triple screen back then). I decided NOT to do the amnio for what many people below have stated. The risk of miscarriage was just too high and I didn't want to risk it. That was with #1 who is nearly 16 now.
With pregnancies #2 & #3, my results also returned to be in the high risk category. I again declined an amnio. I lost #2 about a week after that for unrelated reasons and #3 is just fine and is now turning 13.
I figured, whatever needs the child had, I was still their Mom and God needed me to parent that child. :) God wouldn't give me more than I can handle.
Whatever the results, hang in there and relax. Stress isn't good for the baby anyway ... :)