I would wait for your scan and blood tests, I am currently 31+2 weeks and have been given a 1 in 5 chance of my baby having t21 we refused an amnio and have continued with the pregnancy I don,t feel stressed about waiting but at the end of the day everyone is diffrent and u need to do what is right for u and ure partner, I also have a very healthy 5 year old so I do think these things are one offs and don,t happen twice good luck
Do what ever will make you worry less. Would you worry more during the week or so waiting for the results of the blood test or during the whole 40 weeks until baby is born. I went through the struggle & stress of waiting for the results of a level 2 u/s once my blood screen came back abnormal for T18 but I think that would be easier than worrying the whole pregnancy. & you are right there is a less than 1 % chance of it happening again.
I don't know what the odds are. My only advice is to do what feels right for you.