it also seems reassuring that your ultrasounds came back normal.
i'm no expert but i've heard that the blood tests are frequently inaccurate and can cause more stress and worry than necessary. i have also heard of people who did all of the tests and it came back positive for down's, etc., and that when their child was born it was perfectly healthy. it is for this reason that i am not going to have genetic screening.
i'm also sorry that you are going through this worry, but i would look at the stats on accuracy for the tests themselves.