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Confined placental mosaicism
Mosaicism is where an individual, fetus or baby has more than one type of cell line (types of cell with the same number of chromosomes) is common within the placenta as a result of the high rate of cell division that takes place within this tissue. As a result approximately 1:100 CVS samples will show some evidence of a mosaic pattern, where some cells look normal (i.e. have a normal number of chromosomes down the microscope) and some abnorma. Usually this is a minority of the cells seen. To be sure the cells obtained from the CVS procedure are always grown in culture for 18 days, at which point they are re-examined; at this point the most accurate picture of the fetus/baby's chromosome structure can be obtained and the laboratory is able to give their final result which will either confirm the presence of mosaicism, or (more usually) give a clearer singel cell line result.
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