Hmm, so the testing isn't high sensitivity? It appears that the initial couple had the foetus tested and then did not abort but found that they had a child with Down Syndrome in the end. Interesting.
My daughter was tested (non invasively) as at high risk of downs (the doctor said 50/50) we decided we didn't care... lo and behold: she doesn't have downs. I don't know enough about the area to make judgements, but I am definitely concerned that it's not a slamdunk that the doctors are getting this right.
There is a huge agenda of control around pregnancy in the UK - our consultant was so arsey about us not doing the follow-up that I had to get him changed out (it later turned out that he was struck off 2 years later for more or less murdering a woman and child, but that's another story).
It works by testing tiny amounts of the baby's DNA that can be found in the mother's blood. It is close to 100% effective for detecting Down's Syndrome.
It needs only a blood sample, so carries no meaningful risk for mother or fetus, but it's more expensive than the older amnio or sampling methods, so is usually only available privately (at least in the UK).