I believe that CVS can be taken sooner than the Amnio, but has a higher risk of miscarriage. Amnio is done at approx 16weeks, results taking (in our area) 2 weeks to return.
I have had an amnio in this pregnancy and I would do it again faced with the same dilemma. We were able to afford the Harmony, but still chose Amnio instead as we needed a diagnostic yes or no. Although, I appreciate that the Harmony test comes back with a 1/10000 result which is also incredible results. A friend due a week after me went this route and is completely satisfied with her result.
We were also told that the hormone part of the test was likely to be giving us the high risk result (although I think my age also played a part) but that hormones change daily - so take the test one day and you could be high risk, take it another day and it could come in low, take it another and it could be even higher. Hence why it is a combination of all of the factors that gives the overall result.
The risk of miscarriage with amnio is 1/100 (1%) so is actually very low. You have a 99% chance of everything being absolutely fine, and as our councillor explained - if you had a 99% chance of winning the lottery, you would play. BUT, someone has to be the 1% and that is why there is a risk. The risk of miscarriage increases to 1% over the first 7 days following the procedure, day 3-7 being the riskiest and then reduces down until day 14 where you would go back to a 'normal' pregnancy, with the same associated risks as any other pregnancy.
I just did everything I could to reduce the risks. Work knew what was going on and I took two weeks off (which they kindly signed off as sick). I lay on the sofa and chilled (as much as I could with a 12month old!).
Our results came back clear of all conditions and we didn't miscarry. I am now 35weeks and everything is going smoothly.
We needed to know as its not just about Downs, but also about conditions that are unlikely to make your pregnancy full term or potential very short lifespans after labour.
I hope this isn't too much information, and only you can decide. But I felt that the more I knew, the more I could make an informed choice.
Good luck with whatever you decide xx