The NT test uses ultrasound to measure the clear (translucent) space in the tissue at the back of your developing baby's neck. Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average.
So if the measurment is above a certain amount of milimeteres, the risk is higher. Then, an amnio or CVS test can be performed to either confirm or disprove any abnormalities.
Needless to say this is one more thing I'm stressing over. I'm praying our Nugget has a normal scan. Please keep us in your thoughts tomorrow morning and I'll post the results in the afternoon sometime.