LAUSR

Does the total cytoplasmic volume (TCV) of the zygote and time of pronuclei disappearance (tPNf) affect blastocyst development potential and blastocyst quality? The total cytoplasmic volume of zygote and the time of pronuclei disappearance strongly affect blastocyst development as well as blastocyst quality. Extended embryo culture with blastocyst transfer is considered a useful method for selecting embryos with a high implantation potential. One of the main concerns in the German Embryo Protection Act is that the choice of embryos that have a high potential for successful implantation must be made at the pronucleus stage. The introduction of time-lapse technology enabled comprehensive information regarding the morphology and kinetics of the embryo. Although for the past years, strong correlations between embryo morphokinetics and positive outcomes have been demonstrated, some disagreement concerning the wide application of these parameters into an early-stage embryo selection is still present. The injection time of ICSI was designated as “time zero”, and computer software was used to calculate the time frame between the injection and the moment of pronuclei disappearance (tPNf). The total cytoplasmic volume was calculated 16–18 h after injection based on manually drawn diameters of the zygotes, by the computer. Obtained measurements were later associated with the blastocyst formation potential as well as with blastocyst quality. A total of 187 oocytes from 34 patients undergoing the antagonist cycle for ICSI treatment were evaluated. All blastocysts were cultured in Embryoscope™ according to the manufacturer’s specifications (Vitrolife, Sweden). The Gardner and Schoolcraft scoring system was used to describe blastocyst quality. Statistical analyses were performed using IBM SPSS version 24. Data were reported as median and range. Differences between groups were tested using the Mann-Whitney U test. Statistical significance was defined as p < 0.05. Obtained data showed that the total cytoplasmic volume values were significantly higher in zygotes that reached the blastocyst stage compared with those that did not [708376,268µm³ (560564,412µm³ - 838602,605µm³) vs 674349,917 (415749,353- 823640,638) respectively; p < 0.0001]. Furthermore, this parameter as well significantly affect blastocyst quality where zygotes which formed better blastocyst quality had smaller cytoplasmic volume [685568,079 µm³ (560564,412- 790112,397µm³) vs 745514,662 µm³ (616581,339- 838602,605) respectively; p < 0.0001]. Time of pronuclei disappearance (tPNf) was significantly different (p < 0.0001) in successfully formed blastocysts [22.00h (17–29 h)] versus arrested or non-blastulating embryos [23.00h (17–56 h)]. Zygotes who had a shorter time frame between injection and pronuclei disappearance showed better blastocyst quality values compared with those who had longer time frame [21.00h (17–28h) vs 23.00h (18–29h) respectively; p < 0.01]. The limitation of the presented study was that due to the double-embryo transfer correlation between morphokinetic parameters and pregnancy rate was not possible to be calculated. Further research should link these morphokinetic parameters with pregnancy rate and live birth rate as well. Wider implications of the findings: The potential of the present findings is considerable, especially for countries with strict Embryo Law Regulation. Obtained results might be highly useful for selecting embryos with high implantation potential. In addition, the present work illustrates the possibility of additional information that can potentially be incorporated into an embryo classification model. Not applicable