Cell free DNA (cfDNA) analysis is revolutionising prenatal genetic testing. Rather than subjecting women to invasive tests with associated discomfort and increased risk of miscarriage, analysis of cfDNA (through non-invasive prenatal testing, NIPT and non-invasive prenatal diagnosis, NIPD) is offering pregnant women an earlier, safer alternative.
Because of the close contact between maternal and fetal circulations in utero, a small amount of cell-free fetal DNA (not encased in a cell or nucleus) enters the maternal blood stream.
It originates from the trophoblast (placenta). This can be detected and analysed by taking a blood sample from the mother. Fetal DNA makes up around 10-20% of the total circulating cell free
DNA in the maternal plasma.
The cell free DNA in the maternal plasma comprises both maternal and fetal cell free DNA fractions, and distinguishing one from the other is one of the main challenges of cell free DNA analysis.
The presence of cell-free fetal DNA in maternal plasma and serum was first described by Lo and colleagues in the Lancet back in 1997.
Lo also spoke about how the arrival of whole genome sequencing brought about groundbreaking developments in the field of prenatal diagnosis at the PHG Foundation 15th anniversary conference, ‘Translating genomics: making science work for health’ in 2012.
The earliest stage in gestation that cell-free fetal DNA can be detected 4-5 weeks gestation. How soon after delivery do the cell-free fetal DNA levels fall. It is cleared from the maternal circulation within 30 minutes of delivery.
NIPD refers to the use of cfDNA analysis to diagnose monogenic disorders or to determine fetal sex or rhesus status. It does not require an invasive test for confirmation of the result.
NIPT refers to the use of cfDNA analysis as an advanced screening test for aneuploidy. Whilst this provides an accurate screening test for aneuploidy from 10 weeks’ gestation, positive results require confirmation by invasive testing.
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