kel ... this sucks.

Make a decision from your heart. Obviously figures are giving you nothing right now, so I think you and your DH need to make a choice about the amnio just based on your mummy instinct.
My heart would be saying don't do it; do all the other tests, but don't do that one. I can't back it up; it's just what I feel.

And maybe at your 2nd ultrasound everything will be fine and it turns out it was just a bug squashed on that part of the screen... (OK, completely stupid, I know. But I would love for this never to have happened to you)