The recent discovery of the presence of fetal DNA and fetal cells
in maternal blood has offered new approaches to non-invasive prenatal paternity testing. The concentration of fetal DNA
in maternal plasma was found to be much higher than that present in the cellular fraction. Since fetal DNA in maternal
plasma circulates within the background of maternal DNA, it has been used mainly for non-invasive prenatal diagnosis of paternally inherited
disorders as well as fetal gender.
Fetal cells under microscope
©Health Genetic Center Corp.
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By the use of Y-chromosomal sequences which are unique to a male fetuses a marker, a number of scientific groups
were able to demonstrate that fetal DNA is indeed present in the plasma of pregnant women. The detection rate for fetal DNA in
maternal plasma was much higher than that for DNA from nucleated blood cells extracted from a similar volume of whole blood.
Using real-time quantitative polymerase chain reaction (PCR) technology, investigators have further demonstrated that fetal DNA
is present at very high fractional concentrations in maternal plasma. This high relative concentration suggests that fetal DNA could
be robustly detected in maternal plasma using modern molecular technology. This point has now been confirmed by many groups who
have reported a close to 100% sensitivity at detecting fetal genetic material from maternal blood samples.
As it has been demonstrated that fetal cells can persist for years following delivery, a question has initially been raised
regarding the possible persistance also of circulating fetal DNA from one pregnancy into the next, which may jeopardize the accuracy of
a plasma based DNA test carried out during the second pregnancy. By serial monitoring of women following delivery, scientists have shown
that fetal DNA is cleared very rapidly from maternal plasma following delivery, with a half-life in the order of minutes. These
results indicate that unlike fetal cells in maternal blood, plasma fetal DNA analysis is not complicated by the effects of persistance
prior pregnancies. Both cell-free fetal DNA and fetal cells can be a source of fetal genetic material for non-invasive prenatal DNA testing. To understand the differences between non-invasive (blood test) and invasive (CVS or amniocentesis) prenatal paternity tests, please review the following webpage: Comparison Table
Additional information: read an article in the Science magazine about the non-invasive prenatal technology.
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