Alapala the same thing happened to me just a few weeks ago. Our NHS 12 week scan came back with a risk of 1:169. The sonographer told us she was terribly sorry and suggested we book CVS immediately. It was horrible.
We decided to go for a private scan, which is much more detailed - they can check presence of nasal bone, heart chambers etc which are also indicators. These seemed fine, but my blood test results came back with a risk of 1:19.
After much agonising we decided to go ahead with CVS. NOT because we would have terminated the pregnancy if it came back negative but simply because we couldn't face 6 months of worry and wanted to be prepared.
We did a lot of research and discussed it in detail with an NHS consultant and learned that the risk associated with invasive testing is largely to do with the skill of the practitioner. We decided to go to Professor Nikolaides at the Fetal Medicine Centre.
We had the test which wasn't fun but was quick and relatively painless and, thank god, the results came back negative.
That was three weeks ago and I'm so glad we did it. In the same situation, I would do it again. Incidentally on 1st November the NHS in the UK changed the marker for 'high' risk from 1:300 to 1:150 - so if we had our scan now we would be sent away and told not to worry.
I know it's a sensitive issue and people have very strong opinions for and against testing but you must do what is right for you and if you decide not to have any further tests remember it's just a statistic - actually the odds are very much in your favour.
I really feel for you. Hope our story helps.