Hi Meus
I was pregnant when I was 36; i got a "low" statistical risk (1/550) from the blood test, but i was really obsessed with a possible anormality (just like you seem to be). I decided to do the amniocentesis, whose result indicated everything was normal.
I had discussed with my OBGYN about my decision to do the amniocentesis and she told me that since I was thinking so much about anormality and was so stressed about it, i was right to have the amnio. I was ready to take the risk of miscarriage.
I started to enjoy pregnancy only after the amnio result.
It is really a personal choice, but the key question is, as mentioned sherwes, is whether you would continue the pregnancy regardless of the result of the amnio; if the answer is yes, then what is the point of taking the risk of a miscarriage.