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The true biological father of the fetus should have all of
the paternal DNA markers inherited. The paternal DNA markers
are unique to the fetus, and are unlikely to have similar
matches with a random man within a specific human
population.
If the alleged father(s) lacks several of the fetal’s
paternal markers, he cannot be the true biological father,
and can therefore be excluded from paternity of the fetus.
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.
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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