Embryological characteristics and clinical outcomes of oocytes with different degrees of abnormal zona pellucida during assisted reproductive treatment

Abstract Abnormalities in the zona pellucida (ZP) adversely affect oocyte maturation, embryo development and pregnancy outcomes. However, the assessment of severity is challenging. To evaluate the effects of different degrees of ZP abnormalities on embryo development and clinical outcomes, in total, 590 retrieval cycles were scored and divided into four categories (control, mild, moderate and severe) based on three parameters: perivitelline space, percentage of immature oocytes and percentage of oocytes with abnormal morphology. As the severity of abnormal ZP increased, both the number of retrieved oocytes and mature oocytes decreased. The fertilization rate did not differ significantly among groups. The rates of embryo cleavage and day-3 high-quality embryos in the mild group and the moderate group did not vary significantly between the two groups but were significantly higher than those in the severe group. The blastulation rates of the abnormal ZP groups were similar; however, they were lower than those of the control group. Moreover, the cycle cancellation rate of the severe abnormal ZP group was as high as 66.20%, which was significantly higher than that of the other three groups. Although the rates of cumulative clinical pregnancy and live births were lower than those in the control group, they were comparable among the abnormal ZP groups. There were no differences in the neonatal outcomes of the different groups. Together, ZP abnormalities show various degrees of severity, and in all patients regardless of the degree of ZP abnormalities who achieve available embryos, there will be an opportunity to eventually give birth.