P-126 Investigation of the deterministic value of presence of visible spindle on fertilization and blastocytes utilization potential in frozen/thawed oocyte cycle

Abstract

Abstract Study question Does presence or absence of birefringent spindle after warming of the oocytes has deterministic value on fertilization and early embryonic development potentiaL? Summary answer The warmed oocytes with birefringent spindle seem to have a higher potential to fertilize and become good quality blastocytes. What is known already To date, characteristics of the meiotic spindles in human oocytes were studied by several authors by using a non-invasive method (PolScope) and shown that they are associated with fertilization, embryo quality, pregnancy, and live birth rates. Also, it has been known that meiotic spindle structures are very susceptible to cryodamage and can be disassembled and re-assembled depending on the change in temperature. Thus, studying spindle characteristics of the vitrified-warmed oocytes is important and can provide information about the full recovery of the oocytes, fertilization, embryo development, and pregnancy, which the data is limited in the literature. Study design, size, duration A retrospective study consisting 40 egg donation cycles by using vitrified-warmed oocytes between December 2017 and December 2019 at British Cyprus IVF Hospital. Participants/materials, setting, methods Spindle morphologies of vitrified-warmed oocytes were analyzed by PolScope (RI) combined with an image analysis system after approximately 1.5 hours post-warming. The data is divided into two according to the presence or absence of visible nucleus and correlation with embryonic development analyzed accordingly. To make a comparison in groups a new numerical scoring system for embryo quality on days 5 and 6 was created where embryos scored depending on the stage of expansion, Main results and the role of chance In total, 587 out of 648 vitrified/warmed oocytes survived (90.6%) and 447 of them were fertilized (75.0%). Among the survived oocytes, 503 (85.5%) oocytes were containing detectable spindle (Group I) while spindles were missing in 84 oocytes (Group II). The results showed that the fertilization rate (78.1% vs. 64.3%, p < 0.01), the proportion of good PN morphology (Z Score: Z1 and Z2 over other parameters: 50.4% vs 35.2%, p = 0.036), and viable embryo count (40.6% vs 15.1%, p < 0.01) which is defined as embryos that good enough to transfer or freezing, were higher in group I. Similarly, the degree of expansion on day 5/6 (p = 0.013, p = 0.015 respectively) and the quality of the cells in ICM and TE (p < 0.01) were found higher in group I. We further investigated the differences in embryo quality between groups by converting the embryo grades to numerical value starting from arrested (Score=0) to 6AA (Score=22) and found that embryo scores on day 5 (p = 0.01) and day 6 (p = 0.013) were higher in group I. Limitations, reasons for caution The main limitation of this study is the lack of data regarding the spindle status of the frozen oocytes before vitrification where some of the oocytes might not have visible spindle due to incomplete maturation rather than cryodamage. Wider implications of the findings The present data showed that the presence of birefringent meiotic spindles in warmed oocytes is a very important sign for a full recovery and early embryonic development potential, which can be useful for egg banks and IVF clinics. Trial registration number not applicable