Cell-free fetal DNA (cffDNA) is fetal DNA circulating freely in the maternal blood stream. It can be sampled by venipuncture on the mother. Analysis of cffDNA provides a method of non-invasive prenatal diagnosis and testing.
cffDNA originates from the trophoblasts making up the placenta. An average of 11%-13.4% of cell-free DNA in maternal blood is of fetal origin, although this varies widely amongst patients. The fetal DNA is fragmented and makes its way into the maternal bloodstream via shedding of the placental microparticles into the maternal bloodstream (figure 1). Studies have shown that cffDNA can first be observed as early as 7 weeks gestation, and the amount of cffDNA increases as the pregnancy progresses. cffDNA diminishes quickly after the birth of the baby, so that it is no longer detectable in the maternal blood approximately 2 hours after birth. cffDNA fragments are significantly smaller than the maternal DNA fragments in the bloodstream, with cffDNA fragments being approximately 200bp (base pairs) in size. Many protocols to extract the fetal DNA from the maternal plasma use its size to distinguish it from the maternal DNA.
Studies have looked at, and some have even optimized, protocols for testing for various issues, including non-compatible RhD factors, sex determination for X-linked genetic disordersand testing for single gene disorders. Current studies are now looking at determining aneuploidies in the developing fetus. These protocols can be done earlier than the current prenatal testing methods, and have no risk of spontaneous abortion, unlike current prenatal testing methods. Non-invasive prenatal diagnosis (NIPD) and Non-invasive prenatal testing (NIPT) have been implemented in the UK and parts of the US; it has clear benefits above the standard tests of chorionic villi sample (CVS), amniocentesis, and other techniques which have procedure-related miscarriage risks of about 1 in 100 pregnancies and 1 in 200 pregnancies, respectively.