L26/P-164 First quantitative study of oocyte microinjection-cone shape: impact on fertilization and early embryo development

Le résumé fourni par la source

Abstract Study question Does the oocyte microinjection-cone geometry (deformation angle and area), conditioned by oocyte quality, influence fertilization and early embryo development in ICSI cycles? Summary answer Larger microinjection-cone angles impair fertilization and development, especially in low-quality oocytes. Fertilization appears to be the stage most sensitive to microinjection technique–related factors. What is known already During ICSI, the oocyte membrane forms a characteristic ‘microinjection cone’ as the pipette penetrates the oolemma. Its shape reflects how the membrane breaks and the level of mechanical resistance the oocyte provides. A well-defined, elastic cone suggests normal membrane behavior, whereas an irregular or weak cone indicates increased fragility and a poorer prognosis for fertilization or embryo development. These mechanical patterns are likely influenced by intrinsic oocyte quality and by technical characteristics of the ICSI microinjection process. However, they have rarely been quantified or systematically analyzed, and their potential value as objective, reproducible predictors of reproductive outcomes remain largely unexplored. Study design, size, duration We included 160 ICSI videos comprising 939 MII oocytes. For each oocyte, we captured an image at the moment of microinjection under 20X, 33X or 40X magnification to assess membrane deformation, specifically the shape of the microinjection cone. Poorly focused images were excluded (34%). Biological outcomes were then studied according to the quartiles of the measured oocyte parameters, enabling evaluation of potential associations between mechanical deformation and subsequent developmental results. Participants/materials, setting, methods Fiji program was used to measure the microinjection-cone angle (vertex) and deformed oocyte area (area of the microinjection-cone) using a 120-µm oocyte diameter as scale. Oocyte quality was assessed with Magenta (Future Fertility; score 0-10), to evaluate whether these measurements and their association with reproductive outcomes differed by quality (<5 low; >5 good). Additionally, we fitted generalized estimating equation (GEE) models to quantify the independent and interaction effects of deformation variables and oocyte quality. Main results and the role of chance Our analysis showed that quartiles based on microinjection-cone angle were associated with differences in fertilization and embryo development. Oocytes in Q4 (largest deformation angles) had lower fertilization (FR = 72.65%), blastocyst (BR = 46.58%*), usable blastocyst (UB = 29.91%*), and transferable blastocyst rates (TB = 20.94%*) compared with Q1 (FR 80.85%, BR 59.15%, UB 41.70%, TB 34.04%) and Q2 (FR 78.72%, BR 60.00%, UB 42.12%, TB 28.94%). For microinjection-cone area, Q4 showed higher FR, BR, UB and TB than Q1, with significance for UB (41.28%* versus 27.52%). When stratifying by oocyte quality, poor quality oocytes (score<5) showed that Q4 angles had lower fertilization and developmental rates than Q1, significantly for FR (61.60%* vs 78.71%). For area-based quartiles, Q3 (53.58%*) and Q4 (48.48%) had higher transferable blastocyst rates than Q1 (25.64%) and Q2 (32.43%). In good-quality oocytes (score>5), no significant differences were observed across quartiles. GEE models revealed that oocyte quality assessed by AI-image analysis is the main determinant of embryonic outcomes. However, the microinjection angle shows a significant effect on fertilization, with a non-linear behavior, which is more pronounced in low-quality oocytes (OR = 0.021*,[0.003, 0.040]), indicating that fertilization outcomes are particularly sensitive to the ICSI microinjection technique, whereas at later developmental stages biological factors appear to predominate. (*)=p<0.05. Limitations, reasons for caution Measurements were obtained from static, two-dimensional images, which may not fully reflect dynamic membrane behavior. In addition, quartile thresholds depend on this dataset and may limit generalizability. Finally, operator-dependent technical patterns may partly account for the observed variability in microinjection-cone geometry, which was not included in the GEE models. Wider implications of the findings These findings indicate that high microinjection angles and very small cone areas reflect minimal oolemma resistance, likely associated with both embryologist performance and membrane fragility. Consequently, deformation patterns observed during ICSI may capture underlying oocyte biomechanical properties, providing a potential noninvasive indicator of oocyte and subsequent embryo competence. Trial registration number No

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.