I had the AFP blood test done and it came back as "80 percent chance of Down syndrome". This blood test is not accurate but can help you decide whether you want to go for more accurate testing.
Amniocentesis and CVS tests are absolutely conclusive for genetic abnormalities such as Down Syndrome.
I opted to go for the CVS test rather than amnio when I got the blood results. CVS tests the same thing - the genetic structure of the baby - but its done earlier and its just a bit more risky - a 2 percent chance of miscarriage rather than a 1 percent chance that you have with amnio. But CVS is (or can be) done through the cervix and must be done between the 10th and 12th week of pregnancy. If you go for this test, I'd find out who is the very best at performing it and ask about their miscarriage rate. The amnio is done with a needle through the abdomen I think around the 16th or 18th week of pregnancy and its much easier for a doctor to perform (thats why its less risky).
Inshallah, you will find as I did, that the baby is just fine! I had the test done for all 3 of my boys. for some reason, I just have higher levels in my blood that down syndrome babies have - but my boys are normal.