P-224 Efficiency of MI oocytes matured in MII on the egg retrieval day

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Abstract Study question Are the clinical outcomes of matured MI-eggs (MMI) comparable to MII oocytes? Summary answer The fertilisation and blastocyst rates are lower in MMI, but the proportion of good quality embryos and live birth outcomes are similar in both groups What is known already Controlled ovarian stimulation, combined with conventional in vitro fertilisation or intracytoplasmic sperm injection (ICSI), is considered to be the most effective combination of assisted human reproduction treatment. During gonadotropin stimulation and trigger medication, a large proportion of oocytes complete meiosis in the ovary and are extracted as metaphase II (MII). Oocytes that do not complete maturation are retrieved as germinal vesicles (GV) or metaphase I (MI) oocytes, often discarded in oocyte donation cycles due to their suboptimal quality. Study design, size, duration This retrospective study from January 2021 to December 2023 includes 1074 cycles with 7590 donor oocytes, where 7399 MII and 191 MMI oocytes were microinjected. For pregnancy outcomes, data were collected between January 2021 to December 2022. Clinical pregnancy, defined with a positive b-HCG and fetal heartbeat in 12 week of gestation ssw (FHB), and live birth rates (LB) of 752 transfers were recorded (747 for MII group and 5 for MMI group). Participants/materials, setting, methods Oocytes were denuded at 2h post retrieval and ICSI was performed 2h post denudation. Male factor was not taken into account. Embryos were cultured under the same conditions. Data were collected on fertilisation rates and the quality of obtained blastocyst, grouped into better quality(BQ) (AA, AB, BA, BB) and poorer quality(PQ) (BC, CB, AC and CA). The pregnancy outcomes were calculated with respect to the number of embryos transferred. Data were analysed using chi-square (SPSS26) Main results and the role of chance The obtained results showed significant differences in fertilization rate between MII (72.1%) and MMI (44.5%)(p < 0.001). Likewise, the blastocyst rate was notably higher in MII (54.4%) compared to MMI (22.4%) (p < 0.001). Concerning the distribution between day 5 and day 6, there were no significant differences in both groups (D5: 72.0%MII vs 73.7%MMI and D6: 28.0%MII vs 26.3%MMI; p = 0.870), as well as no differences in the distribution of quality (BQ: 82.0%MII vs 68.4%MMI and PQ: 18.0%MII vs 31.6%MMI; p = 0.124). Regarding transfer outcomes, PR was similar in both groups (63.6% MII and 60.0% MMI, p = 0.870). No significant difference was observed in the FHB rate (50.6% MII vs 60.0% MMI; p = 0.674) or LB rate (33.1% MII vs 40.0% MMI, p = 0.746). Limitations, reasons for caution Although the data suggest that IMM should be used, it should be noted that the number of transfers performed with embryos from IMM oocytes is low. Therefore, the number of embryos from this group should be increased for a more comprehensive evaluation. Wider implications of the findings The results obtained from this study show that MMI oocytes have lower fertilisation and blastocyst rates, but similar qualities and comparable transfer performance; therefore, the results obtained suggest its use Trial registration number Not applicable