To take trisomy 21 as an example (Down's syndrome cause), this means the fetus has three copies of chromosome 21. After a CVS or amnio, the lab will look at the

To take trisomy 21 as an example (Down's syndrome cause), this means the fetus has three copies of chromosome 21. After a CVS or amnio, the lab will look at the cells under the microscope and look for two copies of each chromosome. If they find three instead, that's a chromosome abnormality. If you break open the cells and end up with DNA fragments floating around, it's possible to sequence the DNA but there's not any information that can tell you whether a cell had an extra copy of a chromosome. It's like asking whether the apples to make a cup of juice were all packed in the same box or multiple boxes. Apparently this same researcher does have a down syndrome test, but it is based on measuring RNA ratios and does not seem to rely on sequencing the fetus's DNA at all. http://www.nytimes.com/2008/10/07/health/research/07down.html?_r=1&pagewanted=2 http://www.nytimes.com/2008/10/07/health/research/07down.htm... So I am now confused as to what is being reported in this story. Is this using DNA or fetal RNA?