ZONA PELLUCIDA DYSMORPHOLOGY IS ASSOCIATED WITH LOWER FERTILIZATION RATES IN ICSI

Abstract

Although cytoplasmic dysmorphology of oocytes affects clinical outcomes, the relationship between the dysmorphology of the zona pellucida (ZP) observed during ICSI and clinical outcomes is still unclear. In this study, we aimed to clarify the clinical implications of dysmorphologies of ZP. We studied 3758 non-donor cycles who underwent oocyte retrieval at our private fertility center between January 2018 and September 2020. ZP dysmorphologies included ellipsoid ZP shape, partially overlapping ZP, and misshapen ZP. We defined the 383 cycles in which one or more ZP dysmorphological oocytes were observed in the ICSI procedure as the dys-ZP cycles, whereas 3375 cycles with normal-ZP were defined as the normal-ZP cycles for control. The patient characteristics were compared between the two groups to investigate the causes of ZP dysmorphologies. Furthermore, we compared fertilization rates, embryonic development and clinical outcomes for 550 dys-ZP oocytes and 10,228 normal-ZP oocytes. Fisher's exact test and Mann-Whitney U tests were used for statistical analysis. P<0.05 was considered statistically significant. There were no differences in maternal age or BMI between the two groups. The AMH level (2.41±2.39 vs 2.07±2.72 ng/ml), peak estradiol level at the time of hCG priming (1301.0±874.9 vs 1014.6±785.7 pg/ml), total dose of gonadotropins (2006.4±846.5 vs 1784.3±904.8 IU/ml), and the number of retrieved oocytes (8.69±5.94 vs 6.40±5.25) were significantly higher in the dys-ZP cycle than in the normal-ZP cycle. The incidence of ZP dysmorphologies was significantly lower in low ovarian stimulation (12.3%, 47/382 vs 17.2%, 580/3379). Fertilization rate was significantly lower with dys-ZP oocytes than with normal-ZP oocytes (72.9%, 401/550 vs 77.2%, 7893/10228). Embryo development and clinical outcomes did not differ between these two groups. In seventeen patients with observed ZP dysmorphology in multiple oocyte retrieval cycles (3 or more times), the normal fertilization rate was low (66.1%, 381/585 vs 77.2%, 7893/10228) and more than 3PN rate, degeneration rate, and non-fertilization rate were high (6.8%, 40/585 vs 3.2%, 327/10228; 8.9%, 52/585 vs 5.0%, 507/10226; 14.7%, 86/585 vs 11.7%, 1194/10228) even in oocytes without ZP dysmorphology, compared to other cycles. It was assumed that the AMH level, the dosage of the gonadotropins, and higher estradiol level may be positively correlated with the incidence of ZP dysmorphology. Since ZP dysmorphology can be associated with lower fertilization rates, embryologists should carefully evaluate ZP morphology during ICSI.