From the results of our present study, if none of these four risk factors (a risk of trisomy 21 > 1 in 100, a high risk of both trisomy 21 and trisomy 18, a low PAPP-A and an NT ≥3.5 mm) are present, which occurs in approximately half of cFTS-positive pregnancies, the prevalence of common and atypical abnormalities will be approximately 1.1 and 0.6% respectively, and the residual risk after a negative cfDNA testing will thus be small. This evidence concerns the gene PAPPA and trisomy 18.