Nicolee, I would suggest against it. There is a small risk of miscarriage associated with the test, so if you would keep the baby regardless then don't have the test. Your next scan also looks for Down markers (as well as markers for Patel and Edward Syndromes) so you will have time to get your head around it then if needs be. Another point to note is that any other chromosomal abnormality will spontaneously miscarry - if you miscarry then you can have the foetus checked for a chromosomal problem. This usually occurs in the first trimester, so as you are in the second trimester (congratulations!) then the risk is substantially lower for that. An amnio won't stop you miscarrying, there is no treatment currently to stop that.

However, it is your choice and only you can decide. I wish you all the best for making your decision and sticky vibes for the rest of your pregnancy.