Conclusion
The findings of this systematic review demonstrate that there is
extensive evidence supporting the use of cffDNA for prenatal screening
of the common autosomal trisomies (T21-T18-T13) and SCAs, in singleton
pregnancies. Amongst the autosomal trisomies, T21 had the highest
results, whereas T13 had the lowest ones. As for SCAs, its accuracy
needs to be greatly improved, especially for 45,X0. However, it is a
screening test and not a diagnostic test, hence, all positive cffDNA
results should be followed by a confirmatory procedure, as false
positives can occur. Similarly, a negative result does not discard an
aneuploidy, as false negatives can also occur. Finally, the main reason
for false results is placental mosaicism, and the main cause of no-call
results is an insufficient fraction of cffDNA.