Confined placental mosaicism for 22q11.2 deletion as the etiology for discordant positive NIPT results.

22q11.2 deletion, the most common microdeletion syndrome within the general population, is estimated to have a prevalence of 1 in 3000 to 6000. Non-invasive prenatal testing has recently expanded to include screening for several microdeletions including 22q11.2. Given the expansion of prenatal screening options to include microdeletions, it is important to understand the limits of this technology and the variety of reasons that a discordant positive result can occur. Here, we describe a case of a pregnant woman who received a positive non-invasive prenatal maternal plasma screen for 22q11.2 deletion. Maternal and postnatal neonatal peripheral blood cytogenetic, PCR, and fluorescence in situ hybridization studies were normal, but the placenta was mosaic for 22q11.2 deletion in two of three biopsy sites. This case illustrates both the complexities of pre- and post-test counseling for microdeletion screening and the potential for a discordant positive microdeletion result because of confined placental mosaicism.