L.,
I am not Jewish, and don't have experience with this but I do have something I thought my be helpful.
When pregnant with my son, my second pregnancy in under five months (miscarried and got pregnant even when trying not to), that blood test we get done early on came up with the results that there was a 40% chance my child would be born with downs syndrome. So, my doctor at the time recommended I get a Amnio done to verify.
I really didn't have a lot of information on the process or how it would help, but I followed my doc's advice and went to the specialist. We sat down with a counselor who explained the results, and told us the whole thing about genetics and disorders, syndromes and how all the works. She said that there was a good chance the even the Amnio would not present results that would be definite.
I was even more confused about why were there! When the specialist came in and did his ultrasound he told us that we were having a boy and that he could not see anything conclusive...so, did we want the Amnio??
In a split second, I said 'no'. After getting all the facts about the test and how it's done and that even after all that, I still might not know for sure??? After all, this was my baby and what was I going to do if I found out that he was going to be challenged??
I decided that either knowing or not, wouldn't change that I was already in love with this person who I had created and if there was a challenge ahead of us greater than just raising a child, I would deal with it when the time came.
My son was born premature, 8 wks, but now is now a happy and healthy little boy of 2 years old. No disorders or syndromes...just allergies and lactose intolerance!!
Good luck with your decision!