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  • Is There a Link Between Oocyte Meiotic Spindle Normality and Embryo Euploidy?
    (2019) Tilia, Liza
    Thesis
    Aim: To explore the relationship between oocyte meiotic spindle (OMS) morphology, visualised by polarised light microscopy (PLM) at the time of intracytoplasmic sperm injection (ICSI), with the genetic make-up of the resulting embryo as determined by preimplantation genetic testing (PGT). Method: Three separate studies were performed using similar methodologies. For all studies, the OMS was visualised by PLM at the time of ICSI and classified as normal or abnormal (dysmorphic, translucent, telophase and not visible). The resulting embryos were cultured and PGT was performed by whole genome analysis. Study 1: A single blastomere was biopsied from suitably developed cleavage stage embryos. PGT was performed by whole genome analysis (WGA). Study 2: Trophectoderm cells (3-5) were biopsied from suitably developed blastocysts and PGT performed by WGA. Study 3: Oocytes at metaphase II and late-maturing oocytes (metaphase I at denudation) were compared for developmental markers such as fertilisation, embryo quality and OMS morphology. The data from these studies was analysed by generalised estimating equation to assess the association of OMS morphologies with developmental markers and the resulting embryo ploidy. Result: The probability of embryo euploidy was associated with a normal compared to abnormal OMS whether embryo ploidy was determined at cleavage or blastocyst stage. The sub-classifications of OMS morphology resulted in similar associations with embryo euploidy at both cleavage and blastocyst stage: There was no significant difference in euploidy rate between normal and dysmorphic OMSs. Translucent and no visible OMSs were associated with embryo aneuploidy. No euploid embryos resulted from oocytes with a telophase OMS. The frequency of all OMS morphology types in late-maturing oocytes was significantly different to their sibling mature oocytes. Conclusion: A link does exist between OMS normality and embryo euploidy. Normal OMS morphology is associated with cleavage and blastocyst stage embryo euploidy compared to oocytes with abnormal OMS morphology. Translucent and not visible OMS morphologies are significantly more likely to be associated with aneuploidy, while oocytes identified in telophase were never associated with a euploid embryo, regardless of the developmental stage of PGT. This is the first study to find an association between OMS morphology and embryo ploidy and a non-invasive method of predicting the resulting embryo ploidy.