Outcome data for non‐invasive prenatal testing suggestive of an atypical sex chromosome abnormality of fetal/placental origin

This study was designed to identify outcome data for non‐invasive prenatal testing ( NIPT ) results suggestive of an atypical sex chromosome abnormality of fetal/placental origin. A single‐center descriptive case series was performed between January 1, 2022 and August 1, 2024, which identified 16 cases, 11 of which completed diagnostic testing. Of those 11 cases, only 2 were found to have detectable chromosomal abnormalities of the fetus (monosomy X and mosaic monosomy X). The majority of the 9 cases without detectable fetal chromosome abnormalities cannot be assessed for the presence of confined placental mosaicism due to the lack of CVS testing; however one confirmed case was identified. While this case series is limited in size, it highlights examples that can be used by clinicians in counseling patients about possible outcomes for these atypical NIPT results. These cases also showcase the importance of pre and post‐test counseling, due to the complexity of results. Larger studies are needed to elucidate the mechanisms underlying these findings and to further guide patient counseling.