Morphokinetic features in human embryos: Analysis by our original high-resolution time-lapse cinematography-Summary of the past two decades.

Background: The pioneering work by Dr. Payne et al. in time-lapse cinematography for observation of the morphokinetic features of human embryos inspired us to develop a new in vitro culture system with high-resolution time-lapse cinematography (hR-TLC) back in 2001. Methods: This in vitro culture system was capable of maintaining stable culture and was constructed on an inverted microscope stage. Embryos were observed and photographed noninvasively for an extended period, up to 7 days. The obtained images were displayed at a speed of 30 frames per second and individually analyzed. Results: Using hR-TLC, human fertilization and subsequent embryonic development were visualized, revealing the time course of phenomena and many unusual dynamics. Conclusion: In this review, we summarize the results of our hR-TLC analysis of early human embryonic development over the past 20 years. In the near future, it is expected that the vast amount of information obtained by hR-TLC will be integrated into the AI system for further analysis and to provide feedback that will have the potential to improve clinical practice. In the era of SDGs and environmental awareness, we should be cautious about the direction in which AI can be utilized to avoid any further harm to the planet.

Unstable osmolality of microdrops cultured in non-humidified incubators.

PURPOSE: To investigate the stability of osmolality in non-humidified and humidified incubators for assisted reproductive technologies (ART). METHODS: Drops of three single-step culture media (media A, B, and C) were incubated for 5 or 6 days covered with four different mineral oils (oils A, B, C, and D) in non-humidified incubator A, non-humidified incubator B, or humidified incubator C to investigate the effects of incubator environment (humidification), drop volume, culture media, and mineral oil on the stability of osmolality in microdrops. RESULTS: A significant and linear increase was shown in the osmolality of 50-µL and 200-µL microdrops covered with mineral oil during 5 days incubation in non-humidified benchtop incubators. The maximum increase was 20 mOsm/kg, and the extent of the increase was affected by microdrop volume and possibly by the type of mineral oil used to cover the drops. In contrast, the osmolality of 50-µL and 200-µL microdrops did not change during 5 days incubation in a humidified benchtop incubator. CONCLUSIONS: Mineral oil alone may not adequately prevent gradual changes in the osmolality of low-volume microdrops during extended in vitro culture of human embryos in non-humidified incubators. As a result, the osmolality may increase to high enough levels to stress some human embryos and adversely affect clinical outcomes. We therefore recommend that the stability of osmolality should be given more consideration to ensure optimal culture conditions for ART.

Analysis of compaction initiation in human embryos by using time-lapse cinematography.

PURPOSE: To analyze the initiation of compaction in human embryos in vitro by using time-lapse cinematography (TLC), with the goal of determining the precise timing of compaction and clarifying the morphological changes underlying the compaction process. METHODS: One hundred and fifteen embryos donated by couples with no further need for embryo-transfer were used in this study. Donated embryos were thawed and processed, and then their morphological behavior during the initiation of compaction was dynamically observed via time-lapse cinematography (TLC) for 5 days. RESULTS: Although the initiation of compaction occurred throughout the period from the 4-cell to 16-cell stage, 99 (86.1 %) embryos initiated compaction at the 8-cell stage or later, with initiation at the 8-cell stage being most frequent (22.6 %). Of these 99 embryos, 49.5 % developed into good-quality blastocysts. In contrast, of the 16 (13.9 %) embryos that initiated compaction prior to the 8-cell stage, only 18.8 % developed into good-quality blastocysts. Embryos that initiated compaction before the 8-cell stage showed significantly higher numbers of multinucleated blastomeres, due to asynchronism in nuclear division at the third mitotic division resulting from cytokinetic failure. CONCLUSIONS: The initiation of compaction primarily occurs at the third mitotic division or later in human embryos. Embryos that initiate compaction before the 8-cell stage are usually associated with aberrant embryonic development (i.e., cytokinetic failure accompanied by karyokinesis).