201 Correlation between metaphase II oocyte cytoplasmic granulation patterns and intracytoplasmic sperm injection fertilization outcome in older patients

Abstract

Cytoplasmic granulation is frequently observed in human MII oocytes in fertility clinics from women requiring early egg retrieval (also called highly individualized egg retrieval, with hCG trigger at lead follicle size 16.0-18.0 mm or even less) to avoid premature luteinization. Early retrieval is mostly done for older women (≥36 years old) or younger women with premature ovarian aging. However, only limited reports have focused on detailed analysis of the patterns of cytoplasmic granulation and their correlation with the quality of human oocytes. The aim of this report was to evaluate correlation between granulation patterns of human MII oocytes from early retrieval and the corresponding fertilization rates from intracytoplasmic sperm injection (ICSI). Each MII oocyte was imaged when ICSI was performed. The granulation pattern of each oocyte was reviewed, evaluated, and categorized by the same person as non-granulation (NG, homogeneous, sandy pattern, no granulation or granulation area <1/8 of total cytoplasm), central granulation (CG, ring pattern, a cluster of granules in centre with size >1/4 of oocyte diameter), uneven granulation (UG, sandy-rocky pattern, granulation area >1/8 but <3/4 of total cytoplasm), and dispersed granulation (DG, rocky pattern, granulation area >3/4 of total cytoplasm). Fertilization (pronucleus count, PN) results were then extracted from medical records and matched to the granulation categories. In total, 1759 oocytes done with ICSI in year 2018 were analysed. Fertilization (<2PN, 2PN or >2PN) rates of each group (n = 381, n = 1222, n = 156, respectively) were calculated. Student's t-test was used for group-group comparison analysis. Compared with the NG group, the UG and CG groups had lower 2PN rates (67.2% vs. 84.6%; P < 0.001; 73.0% vs. 84.6%; P < 0.05; respectively) and the DG group had a much lower 2PN rate (43.3% vs. 84.6%; P < 0.001). The UG and CG groups had higher <2PN rates (24.8% vs. 12.1%; P < 0.001; 24.3% vs. 12.1%; P < 0.001; respectively), and the DG group had a much higher <2PN rate (41.1% vs. 12.1%; P < 0.001) than the NG group. For >2PN rates, both UG and DG groups were higher than the NG group (8.0% vs. 3.3%; P < 0.05; 15.6% vs. 3.3%; P < 0.001; respectively), whereas the DG group was higher than the UG group (15.6% vs. 8.0%). These data demonstrated that dispersed granulation was the worst pattern for fertilization. Interestingly, many of the uneven-granulation group oocytes could become homogeneous (non-granulation) after hours or overnight IVM culture, suggesting that uneven granulation might be a sign of incomplete cytoplasmic maturity. Technically, performing ICSI through the less-granulation side was easier because of less resistance to membrane breaking and to pushing sperm out. Discovering the molecular nature of the granules and related cytoskeleton structures would extend our understanding of their existence and improve treatments by adjusting stimulation and trigger accordingly.