P867: A cautionary tale of fetoplacental discrepancies: The impact of mosaicism in prenatal diagnosis

Both cases feature non-mosaic abnormalities in the fetus, likely due to postzygotic errors occurring early in development, and a mix of normal and abnormal cell lines in the placenta. This contrasts with more common scenarios where a rescue mechanism restores diploidy in the lineage that gives rise to the fetus, resulting in the confinement of abnormal cells to the placenta and a normal fetal outcome. These cases highlight the complexity of prenatal diagnosis and the challenges of interpreting discrepant results in the presence of mosaicism.