Expat, I agree completely.
Whilst this thread is abvout the twenty week scan and what it can pick up, it is also important to realise what it doesn't tell you. (I do think that all should have one btw)My son has di georges syndrome a chromosome abnormality that will affect him all of his life. I sailed through that pregnancy thinking all was well, when in fact it wasn't.
Our experience has taught me that whilst he will always have di-georges, it isn't all that he is iyswim, and he will still have a good life.
Twenty week scans are very important though for picking up conditions that are incompitable with life, or those that require immediate treatment after birth.
Good luck with getting your scan makingdo.