I had a high nt measurement (4.2) at my dating scan in April, and was fast tracked for a CVS. Unfortunately the fetal medicine consultant at UCH was unable to get a clear path to the placenta due to it's position, and my bowel loops being in the way, so we were faced with the prospect of having to wait until an amnio could be done at 16 weeks. As it was, the more detailed scan he did before attempting the test flagged up a number of issues (exomphalos, single artery cord, and smaller than expected foetus) which also pointed towards a serious problem.
We went back a week later for another attempt, because we could not face waiting another 3 weeks for an amnio, but the hb had stopped in the meantime. We've just had the results back from tests,
and they confirmed that our son had T13.
Like a pp, I was also told that the miscarriage risk with CVS is higher if there is a problem with the baby. Our combined risk for the main trisomies was 1:5 as my bloods were terrible, so a 1% mc risk was inconsequential to me at that point anyway.
Good luck, I hope things turn out better for you. Please contact ARC (Antenatal Results & Choices) if you need some support, they were really helpful.