a method for concentrating and isolating nucleated cells , such as a maternal and fetal nucleated red blood cells , in a maternal whole blood sample . the invention also provides methods and apparatus for preparing to analyze and analyzing the sample for identification of fetal genetic material as part of prenatal genetic testing . the invention also pertains to methods and apparatus for discriminating fetal nucleated red blood cells from maternal nucleated red blood cells obtained from a blood sample taken from a pregnant woman .