Two cases of placental T21 mosaicism: challenging the detection limits of non-invasive prenatal testing

What's already known about this topic? Confined placental mosaicism (CPM) is a known biological phenomenon that can lead to false positive non-invasive prenatal test results. The small number of false negative non‐invasive prenatal test results reported to date are believed to be because of a low fetal DNA fraction in maternal plasma and/or placental mosaicism What does this study add? The degree and compartmentalization of placental mosaicism can potentially reduce the effective output of fetal DNA into the maternal circulation to steady state levels below the detection limit of non‐invasive prenatal testing, leading to a false negative result