Impact of meiotic spindle imaging on fertilization, embryo development, clinical outcome and morphokinetic parameters: an analysis of 415 in-vivo matured and 317 in-vitro matured human oocyte siblings

To evaluate the relationship between meiotic spindle imaging of in-vivo and in-vitro matured human oocytes and intracytoplasmic sperm injection (ICSI) outcomes. This study was a retrospective observational study conducted at Kyono ART Clinic in Japan from September 2012 to January 2019. This study included a total of 259 ICSI cycles in which were retrieved six or fewer mature oocytes and at least one immature oocyte. ICSI was performed on matured oocytes immediately after denudation. After denudation, MⅠ oocytes were cultured for 4 hours to allow oocyte maturation. We categorized each sibling MII oocyte into an in-vivo matured oocyte group (n=415 oocytes) and an in-vitro matured oocyte group (n=317 oocytes). Both groups, the oocytes’ meiotic spindles were visualized with a Polscope before ICSI. We compared fertilization rate, embryo development and clinical pregnancy rate between the two groups with or without a spindle. Furthermore, 196 embryos (96 in-vivo matured oocytes with spindle, and 7 without spindle; 39 in-vitro matured oocytes withspindle, and 44 without spindle) were analyzed for morphokinetic parameters and incidence of direct unequal cleavage (DUC) by time-lapse imaging (TLS, EmbryoScope+TM). Statistical comparisons between the experimental groups were performed through Fisher’s exact test. Statistical difference was considered to be significant at P<0.05. The mean patient age was 39.0±4.1years (range: 25-45years). The spindle was detected in 85.3% (325/381) and 22.1% (70/317) of the in-vivo and in-vitro matured oocytes, respectively. In both groups, fertilization, blastocyst formation, and good-quality blastocyst rates were significantly higher when spindles were detected (Table). When the spindle was detected, there were no significant differences in fertilization rate or embryo development competence between in-vivo matured and in-vitro matured oocytes. Also, there was no significant difference in clinical pregnancy rate in each group (Table). In the morphokinetic parameters analysis, there were no significant differences in time points of cell division (tPNf to t8), interval of cell cleavage (CC2 and S2), or incidence of DUC. Meiotic spindle imaging may be useful for prediction in both in vitro and in vitro-matured oocyte development. When meiotic spindle is detected in matured oocytes, developmental competence may not be influenced by whether maturation occurs in vivo or in vitro.TableFertilization rate, embryo development and clinical outcomesMeiotic spindle in in-vivo matured oocytesMeiotic spindle in in-vitro matured oocytesDetectedNot detectedDetectedNot detectedNo. of oocytes3255670247Fertilization rate73.2%* (273/373)45.2% (19/42)69.4% * (50/72)49.4% (121/245)Blastocyst rate45.6% * (93/204)28.6% (4/14)34.3% * (12/35)17.7% (17/96)Good quality blastocyst20.1% * (41/204)0.0% (0/14)8.6% * (3/35)0.0% (0/96)No. of vitrified oocytes8331214No. of transferred oocytes6371021Clinical pregnancy rate (fresh and vitrified)28.2% (29/103)25.0% (2/8)16.7% (3/18)8.0% (2/25)*P<0.05 Open table in a new tab