Fetal Fraction – The Essential Factor in Non-Invasive Prenatal Testing
Non-Invasive Prenatal Testing (NIPT), the cell-free DNA-based blood test that screens for fetal chromosomal abnormalities, is fast becoming a routine part of obstetric care.
NIPT at a glance
During pregnancy, maternal plasma contains fragments of DNA from the mother and from the placenta (fetal DNA).
The proportion of DNA fragments from particular chromosomes is usually very stable throughout pregnancy. If there is an excess of fetal fragments from one chromosome, the proportion of fragments from that chromosome will be changed.
A key reason that NIPTs should precisely measures the amount of fetal DNA in the sample – the fetal fraction – is if there is insufficient fetal DNA, the result may merely reflect the genetic status of the mother.
NIPT assays should report a result only if there is sufficient fetal DNA to be confident of accuracy.