Well, I haven't had an amnio, although I did do the CVS (chorionic villus sampling) with my 28 month old. That was done between 10-13 weeks and is considerably more risky (1:200 miscarriage chance vs. approx. 1:400 for amnio) and although the information was reassuring and I got it very early, by 13 weeks (I was 40 at the time) and I know many women who have also done CVS, it was stressful for me.
I understand the earliest you can do an amnio is around 15 weeks; ok this takes me off track a bit to ask how pregnant are you now, do you live near a large university hospital, would you be interested in a much less invasive, although not totally absolute method of determining whether or not an amnio is even necessary? That is, an early ultrasound and two blood draws.
That's what I did with this baby (now 32 weeks), got very reassuring results and so did not do an amnio.
Write me back, or pm me and I'll tell you more if you're interested.
I can also write more about the practicalities of amnio - when it's done, what you do afterwards, etc.
It's big stuff to think about - I've been there a couple of times...