L26/P-169 Comparable euploidy rates in embryos derived from in vitro matured MI and in vivo matured MII oocytes: a 1:1 matched analysis of 214 oocytes

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Abstract Study question Does the spontaneous in vitro maturation (IVM) of MI oocytes affect the ploidy of resulting embryos compared to sibling in vivo matured MII oocytes? Summary answer Embryos from MI oocytes matured in vitro show euploidy rates comparable to those from vivo matured MII oocytes (48.6% vs 45.8%, aOR=0.9, 95% CI:0.5-1.7, p = 0.758) What is known already While in vivo matured MII oocytes are known to reliably produce euploid embryos, the chromosomal competence of MI oocytes that mature spontaneously in culture is less clear. Evaluating euploidy in embryos derived from these oocytes is essential to understand their intrinsic developmental potential. Study design, size, duration Retrospective multicenter 1:1 matched cohort study including 214 PGT-A tested blastocysts from IVF cycles between 2019 and 2026. Among 10,125 tested embryos, 107 derived from MI MIV oocytes were matched to 107 derived from in vivo matured MII oocytes using propensity score matching. Matching covariates included maternal age, oocyte type, origin, and clinic. Participants/materials, setting, methods Blastocysts from IVF cycles at two Spanish clinics were derived from MI oocytes cultured using the same protocol as MII oocytes and that matured in vitro (extruding the first polar body before ICSI). They were matched with blastocysts from MII in vivo oocytes. Cohorts were balanced for age (median 36), type (97.2% fresh), origin (66.4% own), and clinic. Ploidy was assessed by PGT-A via NGS; analysis included Stuart-Maxwell tests and conditional logistic regression. Main results and the role of chance After perfect matching (all p = 1.000), euploidy rates were comparable: 45.8% (MII) vs 48.6% (IVM). Aneuploidy rates: 50.5% vs 49.5%. Global Stuart-Maxwell test showed no distribution differences (p = 0.679). Conditional logistic regression revealed no significant aneuploidy risk increase with IVM (aOR=0.9, 95% CI:0.5-1.7, p = 0.758). Mosaics were rare (3.7% vs 1.9%, insufficient for analysis). Limitations, reasons for caution Retrospective design limits causal inference. Mosaic embryos were too few for meaningful analysis. Single genetic testing platform was used. Generalizability to all patient populations requires confirmation. Despite matching, residual confounding cannot be excluded. Wider implications of the findings The spontaneous in vitro maturation of MI oocytes in standard culture medium does not reduce euploidy in resulting embryos. This demonstrates that MI oocytes reaching MII in culture retain chromosomal competence comparable to in vivo matured MII oocytes, highlighting their intrinsic developmental potential. Trial registration number No

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