Elucidation of abnormal fertilization by single-cell analysis with fluorescence in situ hybridization and polymorphic marker analysis

Objective: To analyze the genetic composition of oocytes and embryos presenting abnormal fertilization. Design: Case report. Setting: In vitro fertilization unit of a university-affiliated hospital. Patient(s): A couple with unexplained infertility with abnormal fertilizations in nine failed IVF-intracytoplasmic sperm injection cycles characterized by the presence of embryos with only one pronucleus and nonextrusion of the second polar body. Intervention(s): All first polar bodies and blastomeres were analyzed by fluorescence in situ hybridization for chromosomes 13, 18, 21, X, and Y. Because some of the one-pronucleus embryos were found to be diploid, they were subjected further to single-cell polymerase chain reaction analysis with use of a panel of highly polymorphic markers from chromosomes 6, 7, 17, 19, X, and Y. Main Outcome Measure(s): Fluorescence in situ hybridization analysis of polar bodies and blastomeres and polymorphic marker analysis of day 5 embryos. Result(s): Fluorescence in situ hybridization analysis of the first polar body demonstrated normal segregation of chromosomes in meiosis I. Fluorescence in situ hybridization analysis of two aspirated blastomeres demonstrated three diploid and two mosaic triploid embryos. Polymorphic marker analysis, however, demonstrated that all embryos, including the diploid ones, had two sets of maternal alleles. Conclusion(s): Single-cell genetic analysis routinely used for preimplantation genetic diagnosis may provide insight into the genetic composition of oocytes and embryos. These data may be used in cases of abnormal fertilization or impaired embryo development for evidence-based fertility counseling regarding prognosis and treatment options.