#148 : A Comprehensive Analysis of the Cells Originating from Tripolar Mitosis in the Preimplantation Embryo

Abstract

Background and Aims: Tripolar mitosis (TM) is cellular division resulting in three daughter cells instead of the typical identical two. Historically studies have grouped all types of aberrant mitosis together providing insufficient evidence to make clinical decisions. This study examined the fate of tripolar mitosis daughter cells and their impact on embryo development and clinical outcomes. Method: A retrospective analysis of 14,450 embryos cultured in EmbryoScope+ was conducted. Embryos were assessed for cleavage stage TM events; mitosis with two concurrent cleavage furrows. TM embryos were categorised by the mitotic cycle of the TM event; Mitosis 1 (TM1), Mitosis 2 (TM2), Mitosis 3 (TM3) or multiple TM (MTM). TM embryo clinical outcomes were compared to embryos from the same IVF cycles. Timelapse footage was used to assess TM daughter cells outcomes. Results: The incidence of TM embryos (n=448) was 3.1% (TM1 n=118, TM2 n=206, TM3 n=98, MTM n=26). TM1 embryos displayed significantly later pronuclei fade times than control embryos (26.7 vs 25.0 HPI, p<0.001) and first cleavage time (29.7 vs 28.1 HPI, p<0.001). Utilisation rate for TM1 (6.6%), TM2 (39.3%) and MTM (11.6%) was significantly reduced compared to control embryos (53.4%, n=2,432, p<0.001). TM3 embryos showed no reduction in utilisation (59.2%). TM embryos demonstrated significantly lower clinical pregnancy and live birth rate (26.8% & 19.6% respectively, n=56) compared to control embryos (45.7% & 34.5%, p<0.01). TM1 embryos had no clinical pregnancies (n=5). At the compaction stage 98.1% of TM embryos had excluded cells. In 97.0% of cases excluded cells originated from TM daughter cells. Trophectoderm biopsy yielded no significant difference in euploidy rate between TM (46.1%) and control (40.1%) embryos. Conclusion: TM1, TM2 and MTM embryos displayed significantly reduced developmental potential. TM3 did not appear to be detrimental to embryo development. Despite TM not affecting euploidy, TM embryos demonstrated lower implantation potential and live birth rate.