Embryonic origin of XX/XY chimerism in an in vitro fertilization–conceived individual

Objective: To report an adult case of XX/XY chimera resulting from in vitro fertilization with transfer of three embryos, that was discovered with preconception genetic carrier screening. Design: Case report. Subject: A 33-year-old nulliparous woman who was conceived via in vitro fertilization with three embryos transferred presented for embryo banking for future family building. Exposure: Genetic carrier screening panel. Main Outcome Measures: Genomic analysis of recessive gene carrier status. Results: An inconclusive genetic carrier screening result led to further investigation that revealed two distinct cell lines, one containing Y-chromosome material, confirming the diagnosis of chimerism. Conclusion: There may be an undiagnosed population of human chimeras resulting from the transfer of multiple embryos with assisted reproductive technologies. The biologic and clinical implications of congenital chimerism are incompletely understood.