P-184 Morphokinetic analysis of cases with vitrified-warmed oocytes in oocyte donation program

Abstract

Abstract Study question Does vitrification of oocytes in oocyte donation program alter the morphokinetic pattern of human embryos? Summary answer Both the extrusion of the second polar body (tPB2) and the appearance of the pronuclei (tPNa) occur earlier in vitrified oocytes without affecting further development. What is known already Vitrification of oocytes has been a breakthrough in oocyte cryopreservation and significantly altered practices in IVF labs. Oocyte vitrification/warming has become an integral part of daily routine and thorough assessment of its efficiency is crucial. Though, studies of vitrified-warmed oocytes have shown similar fertilization, cleavage, blastulation, pregnancy and live birth rates to fresh oocytes, the morphokinetic pattern of embryos originating from vitrified oocytes has not been thoroughly studied. According to some studies vitrification may be related to delayed blastocyst formation while others failed to see any alteration in the morphokinetic pattern between embryos derived from fresh or frozen oocytes. Study design, size, duration This retrospective observational study was performed at Embryolab Fertility Clinic, in Thessaloniki, Greece between April 2020 and September 2021 and included 590 vitrified oocytes from 68 oocyte donation cycles. Control group consisted of 31 good prognosis cases (oocyte donation cycles or homologous oocyte cycles of women under 35 years old). Participants/materials, setting, methods 68 vitrified oocyte donation cycles and 31 fresh control cycles were analyzed. All oocytes after ICSI were cultured in Embryoscope time-lapse incubator up to blastocyst stage. Key time parameters and dynamic events were analyzed using generalized estimating equations (GEE) regression analysis for the non-independent nature of the data. Moreover, the following comparisons were performed between groups: fertilization, cleavage, top cleavage, blastocyst, top blastocyst and pregnancy rates. Main results and the role of chance There was no significant difference in fertilization rates between control and frozen oocytes (77.79% ± 15.73 vs 71.26% ± 21.50 respectively, p = 0.15). Cleavage rate and top cleavage rate (more than 6 cells, equal size, with no or minor fragmentation), were higher in frozen oocytes with this difference being significant (p = 0.02 for cleavage rate and p = 0.015 for top cleavage rate). Blastocyst rate and top blastocyst (2AA, 3AA, 3AB, 4AA, 4AB according to Gardner criteria) rate, though, showed similar rates with no statistically significant difference (Blastocyst rate: 74,15% ± 17.19-control vs 76.42% ± 30.75-frozen oocytes, p = 0.6 & Top blastocyst rate: 45.54% ± 24.04-control, 45.30% ± 32.04-frozen oocytes, p = 0.82). Pregnancy rates were not significantly different (control:85.19%, frozen oocytes:75.38%, p = 0.29). The comparison for key time parameters and dynamic events that were analyzed (tPB2, tPNa, tPNf, t2, t3,t4, t5, t6, t7, t8, t9+, tSC, tM, tSB, tB, tEB, S2, S3, S5, CC1, CC2, CC3,Compaction and Blastulation) showed significant difference in 2 time parameters: tPB2 (4.62 hours-control, 3.67 hours-frozen, Coef: -1.09, p = 0.015) and tPNa (9.07 hours-control, 8.25 hours-frozen oocytes, Coef: -1.06, p = 0.043). Limitations, reasons for caution The fact that the oocytes under comparison were not sibling as well as its retrospective nature, constitute the main limitations of the present study. Moreover, the number of cases included in this study was limited and the available information about ongoing pregnancy and live births is still pending. Wider implications of the findings tPB2 and tPNa seem to occur earlier in vitrified oocytes without affecting further development, implying a need for reviewing timings between OPU/vitrification/warming/ICSI. Moreover, vitrified oocytes displayed higher cleavage and top cleavage rates with unaffected blastocyst or pregnancy rates. Overall, vitrification of oocytes seems to be safe and reliable. Trial registration number N/A