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This test uses both fetal cells and fetal DNA isolation from
maternal blood. During pregnancy, a variety of cell types of
fetal origin, as well as fetal DNA, cross the placenta and
circulate within maternal peripheral blood. This fetal
material is a source of information about the gender and
genetic makeup of the developing fetus. Fetal genetic
material can be detected in maternal blood early in
gestation.
The rarity of fetal nucleated
cells in maternal blood has made their isolation
particularly challenging. To obtain quantities
sufficient for analysis, the use of enrichment techniques is required. The
investigators begin with a 30 ml maternal venous blood
sample.
An initial enrichment step facilitates removal of
many maternal non-nucleated cells through density gradient
centrifugation. Subsequent "purification" of fetal cells is
performed by:
- efficient magnetic cell separation technology and;
- cultivation of fetal progenitor cells.
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The detection of fetal cells in
maternal plasma is much simpler and more robust than the
detection of fetal nucleated cells in maternal blood, and
does not require prior enrichment. In fact, the
concentration of fetal DNA in maternal plasma expressed as a
percentage of total DNA has been measured from 0.39% (the
lowest concentration measured in early pregnancy), to as
high as 11.4% (in late pregnancy).
This approach has been shown
to have application in the prenatal diagnosis of fetal
rhesus D status, sex-linked disorders, fetal sex
determination, and paternally inherited genotyping. In
addition to maternal plasma, fetal DNA can also be detected
in maternal urine; however, the sensitivity of detection is
lower.
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