Kel, I think the OP's have given you great advice. Consider what you would do with the results of the amnio. If you would consider termination should the amnio show that something is wrong then perhaps the risk is worthwhile. If you would not consider termination but you are looking for information and/or reassurance then perhaps it would be better not to have the amnio but to go ahead and have the other tests which can provide you with information but not carry the same risk to you or bub.

If you simply cannot decide whether to go ahead with the amnio, is it possible to have the repeat US a week after the first (another 4 or 5 days, I think?) instead of two? Is a week long enough that the measurement is likely to have changed? You could then make the decision based on the result of the next US. If the measurement is less, no amnio. If the measurement is greater, perhaps that is the little push you need to decide to go ahead with the amnio. And if the measurement is the same then you have a few days up your sleeve to decide what you want to do.

I have also heard that the Monash Genetic Counseling Group are excellent, I know several people who have dealt with them. I don't know what area you are in but perhaps an appointment at Monash with a genetic counselor would provide you with more information?

I know it is little comfort Kel, but as you said the odds are all on your side that your bubba will be just fine. There is plenty of support here for you, whatever you decide to do.