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.

Removing the zona pellucida can decrease cytoplasmic fragmentations in human embryos: a pilot study using 3PN embryos and time-lapse cinematography.

PURPOSE: The aim of this study was to establish a new method of decreasing cytoplasmic fragmentation in early-stage human embryos. METHODS: The zona pellucida (ZP) of abnormally-fertilized oocytes (zygotes with three pronuclei (3PN)), which were donated by patients, was removed at the pronuclear stage. ZP-free embryos were observed in a time-lapse imaging and culturing system in order to examine developmental morphology and embryonic quality. RESULTS: Based on a modification of Veeck's criteria, 47 of 69 ZP-free 3PN embryos (68.1%) showed fragmentation of less than 20% of the total volume of cytoplasm at the first cleavage (grades 1 and 2), 17 (24.6%) showed 20-40% cytoplasmic fragments (grade 3), and only 5 (7.2%) showed more than 40% fragments (grade 4). These results suggest that the rate of fragmentation is decreased by ZP removal before the first cleavage, compared with normal (ZP-intact) 3PN and 2-pronuclear/2-polar body embryos. CONCLUSIONS: This study revealed that the ZP is not always necessary for normal development after the pronuclear stage because the ZP-free embryos studied herein developed normally, maintained their cell adhesion well, and showed a decreased rate of fragmentation. This innovative culture system might provide the major breakthrough needed for patients who have difficulty obtaining good-quality embryos.

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.