Injection funnel persistence time and oolemma resistance during intracytoplasmic sperm injection and subsequent embryo development

OBJECTIVE This study aimed to investigate whether the injection funnel persistence time and oolemma resistance during the intracytoplasmic sperm injection (ICSI) are associated with subsequent embryo quality. DESIGN A prospective observational study at a university hospital. METHODS One hundred and twenty normal-appearing metaphase II oocytes were collected from 54 ICSI cycles. Injection funnel was observed at 0, 30, 60, and 90 s after ICSI, and the injection funnel persistence time was assigned to "no funnel," "0-30," "30-60," "60-90," and ">90 s." The degree of oolemma resistance during ICSI was recorded as "no," "mild," "moderate," and "severe." Subsequent embryos on day 3 after ICSI were evaluated morphologically, and formation of top-quality embryo and embryo score was assessed. We newly developed "oolemma score," based on the injection funnel persistence time and oolemma resistance, and the predictability of top-quality embryo was assessed. RESULTS Among the five groups by injection funnel persistence time, the proportion of top-quality embryo and embryo score (64.3%, 32) was highest in the "30-60 s," but not significant. Among the four groups by oolemma resistance, the proportion of top-quality embryo and embryo score (53.7%, 32) was highest in "no group." The proportion of top-quality embryo in "no group" was significantly higher than "moderate group" (p = 0.012) and "severe group" (p = 0.043). The median embryo score in "no group" was significantly higher than "severe group" (p = 0.041). Newly developed "oolemma score" could predict well the formation of top-quality embryo with a statistical significance (cutoff >14.5, area under the curve 0.695, p < 0.001). CONCLUSION Embryo quality or score is more closely associated with oolemma resistance during ICSI. New "oolemma score" would help to identify embryo developmental potential of each mature oocyte in ICSI cycles.