Oh Iwonka, I'm sorry to hear that you're having such an unpsetting and stressful time. I went through similar stuff with DD, and I know how difficult it can be to get your head around what you're hearing.
A few things to keep in mind which may ease your anxiety:
Firstly the fact that everything looked good on your scan, means they didn't see a significantly high nucal fold measurement or any other soft markers for things like Downs. They also didn't see any fluid around organs or any under-development. This is all REALLY good news. They haven't actually SEEN anything worng with your baby.
Did they give you a ratio based on your bloods for the main trisomies?
If they just said 'high risk' it's worth bearing in mind that they consider a 1:250 chance of an abnormality as "high risk" - but that looked at another way, it also means that there's a 249:250 chance that everything is fine. If I was a betting person I know where I'd lay my cash.
All there are saying at the moment is that your blood results indicate it may be worth some further investigation. This is ALL they are saying, really. Try to keep that in mind and try and stop running worst case scenarios in your head.
An amnio is quite a scary prospect - I had something similar (called a CVS) with DD. I was dreading it, but it didn't end up being half as bad as I imagined. You'll probably see a really good consultant who can discuss the actual risks with you (not just the general ones we all hear about), his/her own opinions on the testing. They will probably also do a more thorough scan which may in itself help ease your concerns a bit. And you can decide not to go through with it AT ANY POINT. It may be worth going along to the appointment and talking to the consultant even if you've not made up your mind about whether to have the amnio.
And it might help to hear that even though we ended up with pretty terrible ratios (1:80 for Edwards and 1:150 for Downs, I think and another one I forget) our DD was and is perfectly healthy.
All is not gloomy - there is in fact every chance your baby is perfectly healthy and well. Try and hold on to the positives and try not to dwell on the what-ifs. Continue to love and cherish your little one as you have been - whatever the outcome they need that more than anything else.
Big hugs to you sweetheart. I know how awful it is, and that no-ones words can really offer much comfort.
Concentrate on the good things that you KNOW - there are many positives here.
((((hugs))))
db
xx