Relationship between morphology of tripronuclear embryo and chromosomal abnormalities potential in intracytoplasmic sperm injection cycles

Introduction: Tripronuclear (3PN) zygote is a frequently observed abnormal outcome in vitro fertilization/intracytoplasmic sperm injection (ICSI) technology. They are usually discarded because of concerns about their abnormal chromosomal constitution. However, in rare cases when availability of the embryos is limited, evidence-based information on the suitability 3PN zygotes for implantation will be valuable. Materials and Methods: In this study, we analyzed the chromosomal constitution of 3PN to investigate the relationship between their morphology and chromosomal status. Thirty 3PN zygotes developed into embryos from 18 cycles were reviewed during 6 months. Biopsies were performed on day 5/6 and were subsequently screened for chromosomal status using a next-generation sequencing method. Results: Of the 30 3PN screened, 66.7% were chromosomally abnormal. At the cleavage stage, there was no association between any of the morphological features and chromosomal status. In contrast, at the blastocyst stage, a grade <3 blastocyst expansion had a significantly higher chromosomal abnormality (90%, P = 0.05) than the other grades of expansion. Embryos with grade non A (grade B and C) for both inner cell mass and tropectoderm, had significantly higher chromosomal abnormalities (100%, P = 0.001 and 93.3%, P = 0.001, respectively). Conclusion: We concluded that chromosomal status and 3PN morphology are linked at the blastocyst stage, and thus morphological assessment of 3PN blastocysts can be used in conjunction with preimplantation genetic screening to select which embryo should be transferred when no other embryos from two pronuclear ICSI zygotes are available.