Originally Posted by jlross67
Hi everyone, I'm new here and hope you can help. I am 21 weeks pregnant and my FISH test came back 90% normal and 10% with a "mosaic" pattern. I have no idea what to make of this. There is little to no information available on the FISH. The results of the amnio probably won't be back until early next week but it would be nice to know what this means. Help!
The FiSH test works by labeling specific chromosomes (by targeting unique DNA sequences in them). Because the point of FISH is to get a quick result they do not culture the cells the same way they do for full karyotyping [chromosome characterization] and thus, they do not necessarily "capture" the cells during the part of the cell cycle when they have exactly 23 pairs of chromosomes [called metaphase] and by necessity some of the cells will have more chromosomes [because they are caught in the stage of DNA replication before division]. Therefore, to be able to get a meaningful result they count the chromosomes present in a number of cells [in the hundreds]. The result you are quoting says that of the hundreds of cells they counted, 90% of them are normal. The remaining 10% showed mosaicism, which means that in those cells there have been chromosomal rearrangements. Since the amniotic cells are cells that have been shed, the way I would interpret these results is that that 10% is the precent of cells that are the oldest in terms of when they were shed by the fetus and are in either the process of dying -something totally normal, that's why they are shed...because the fetus doesn't need them. When cells die like this they do all kinds of crazy things and undergo dramatic changes -including changes to the chromosomes themselves.
If my wife and I get these results we'd be jumping up and down with joy...