I am feeling that it is really important to clarify some things -

Nuchal Translucency Test is an ultra sound combined with a blood test for "free bhcg" and PAPP-A. In babies with chromosomal abnormalities the hcg is within higher limits and the pappA is low. The nuchal fold measurement will be higher in most but not all babies with chromosomal abnormalities.

Nuchal Translucency is not right or wrong - you cannot get a positive or a negative. Itis inaccurate and misleading to think the test was wrong if you got a less favourable result. For example you may have a nuchal measurement of 4.7 combined with a hcg of 46 and a PappA of 3.6. This may give you a risk of 1:170. In many practices a risk of lower than 1:200 a woman may be advised to seek a cvs or amniocentesis. If the results (of the invasive testing) came back clear this does not mean the NT was incorrect - it means you fell within that 1:170 but thankfully all was well.

You will get a risk for age asessment that may look something like: 1:700 - meaning of 700 women with this result 1 will have a child with a chromosomal abnormality.

This test is NOT a "downs syndrome test". Trisomy 21 is coloquially known as "Down's Syndrome (after the doctor that named the disorder). Other Trisomies also manifest with enlarged nuchal fold and blood tests. There are many other chromosomal abnormalities beside Trisomy 21. Trisomy 21 is the most common.

CVS has a higher miscarriage rate than amnio - mainly because the test requires a small amount of the placenta to be snipped and tested. CVS can be done earlier than amnio.