The discovery of cell-free fetal DNA (cffDNA) in maternal blood and high-throughput DNA sequencing technologies (Next-Generation Sequencing, NGS) have paved the way for new non-invasive testing in prenatal medicine (NIPT). Thanks to NGS, cell-free DNA in maternal circulation can be isolated and sequenced after enrichment. All NIPTs require an adequate fraction of fetal DNA which increases during pregnancy and should not be below 2.7% of total cell-free DNA.
Given that fetal and maternal DNA differ from each other, a quantitative analysis of a sufficient amount of sequence reads allows a highly reliable detection of fetal aneuploidies such as trisomy 21 (Down Syndrome), trisomy 18 (Edwards Syndrome), trisomy 13 (Patau Syndrome) or gonosomal defects (Klinefelter Syndrome, Ullrich-Turner Syndrome).
The statistical evaluation yields an adjusted risk or Normalized Chromosome Value (NCV) with threshold value. If the result is not adequately precise (i.e. due to a low fetal fraction), it is recommended to repeat the test or to confirm the result by invasive prenatal diagnostics.
Chromosomal structural changes, translocations or mutations in single genes cannot be detected by NIPT.