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.

Clinical outcomes of personalized blastocyst embryo transfer after endometrial receptivity analysis: A multicenter, retrospective cohort study.

Purpose: To evaluate clinical outcomes after endometrial receptivity analysis (ERA). Methods: This was a multicenter, retrospective cohort study involving 861 women who underwent ERA testing at certified fertility clinics in Japan, and who received subsequent personalized blastocyst embryo transfers (ET) between 2018 and 2020. Clinical outcomes, including pregnancies, miscarriages, and live births, were evaluated according to receptivity status for ERA. Results: Mean patient age was 37.7 years (SD = 4.0), and the median number of previous ETs was 2 (interquartile range, 2-3). 41.0% (353/861) of patients were non-receptive for ERA testing. Clinical pregnancy, miscarriage, and live birth rates for personalized blastocyst ET were 44.5% (226/508), 26.1% (59/226), and 26.8% (136/508) for receptive patients, and 43.1% (152/353), 28.3% (43/152), and 28.9% (102/353) for non-receptive patients, all statistically nonsignificant. Multiple logistic regression demonstrated similar nonsignificant associations between receptivity and clinical outcomes. Greater patient age, smoking, and longer duration of infertility were significantly and negatively associated with receptivity, whereas a history of delivery was positively associated and statistically significant. Conclusions: Clinical outcomes after ERA testing were similar between receptive and non-receptive patients. Further prospective study including an appropriate comparison group are warranted to evaluate the efficacy of ERA testing.

Anthropometric measurements of term singletons at 6 years of age born from fresh and frozen embryo transfer: A multicenter prospective study in Japan.

Purpose: The purpose of this study is to compare anthropometric measurements between term singletons conceived via fresh embryo transfer (FreET) and frozen embryo transfer (FET) and those born via natural conception (NC) or fertility treatments milder than assisted reproductive technology (non-ART) at 6 years of age. Methods: A total of 8149 children were enrolled, and questionnaires about anthropometric measures (weight, height, BMI) were addressed to parents, when the children were 1.5, 3, and 6 years of age. A total of 3299 term singletons were enrolled at birth: 533, 476, 916, and 1374 in the NC, non-ART, FreET, and FET groups, respectively. Results: A total of 1635 term singletons (290, 176, 467, and 702 in the NC, non-ART, FreET, and FET groups respectively) were enrolled until 6 years of age (follow-up rate, approximately 50%). When non-ART group was used as control, the FreET children were 1.0 cm taller than the non-ART children at 6 years of age, after adjusting for confounding factors. However, no differences were observed in the anthropometric data among the non-ART, ART, and NC children at 6 years of age. Conclusion: At 6 years of age, term singletons were taller in the FreET group than in the non-ART group, after adjusting for confounders.

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.

Assessment of developmental potential of human single pronucleated zygotes derived from conventional in vitro fertilization.

PURPOSE: The aim of this study was to non-invasively validate the developmental potential of human single pronucleated (1PN) zygotes derived from conventional in vitro fertilization (c-IVF) at the zygote stage. METHODS: Fifty 1PN zygotes derived from 45 patients undergoing c-IVF were used. Immunohistochemistry and fluorescence live cell imaging were used to confirm normal chromosome segregation during the first mitosis. The usefulness of measuring pronuclear diameter was assessed on the basis of the presence or absence of a proper first cleavage and validated by subsequent development. RESULTS: Although approximately 80% (15/19) of 1PN zygotes contained a diploid genome, immunohistochemistry revealed an unequal distribution of paternal and maternal genomes at the first mitosis. Fluorescence live imaging revealed that 73% (8/11) of 1PN zygotes formed a functional mitotic spindle at the first mitosis resulting from diploid genomes, with 25% (2/8) of these forming a tripolar spindle. 1PN zygotes in which the pronucleus disappeared and that subsequently underwent cleavage had a pronuclear diameter ≥ 32.2 µm. The selection of 1PN zygotes based on pronuclear diameter resulted in zygotes that all formed mitotic spindles with poles during cleavage. Furthermore, 63% (5/8) of these zygotes reached the blastocyst stage. CONCLUSIONS: This study demonstrates the usefulness of a non-invasive assessment of 1PN zygotes derived from c-IVF as an indicator of developmental potential. Furthermore, diploid 1PN zygotes do not always exhibit normal chromosome segregation at the first mitosis. A pronuclear diameter ≥ 32.2 µm just before PN breakdown might be a useful criterion to assess 1PN zygotes that are capable of further development.

Observation of human embryonic behavior in vitro by high-resolution time-lapse cinematography.

Assisted reproductive technology (ART) has yielded vast amounts of information and knowledge on human embryonic development in vitro; however, still images provide limited data on dynamic changes in the developing embryos. Using our high-resolution time-lapse cinematography (hR-TLC) system, we were able to describe normal human embryonic development continuously from the fertilization process to the hatched blastocyst stage in detail. Our hR-TLC observation also showed the embryonic abnormality of a third polar body (PB)-like substance likely containing a small pronucleus being extruded and resulting in single-pronucleus (1PN) formation, while our molecular biological investigations suggested the possibility that some 1PN embryos could be diploid, carrying both maternal and paternal genomes. Furthermore, in some embryos the extruded third PB-like substance was eventually re-absorbed into the ooplasm resulting in the formation of an uneven-sized, two-PN zygote. In addition, other hR-TLC observations showed that cytokinetic failure was correlated with equal-sized, multi-nucleated blastomeres that were also observed in the embryo showing early initiation of compaction. Assessment combining our hR-TLC with molecular biological techniques enables a better understanding of embryonic development and potential improvements in ART outcomes.

Diagnosis of abnormal human fertilization status based on pronuclear origin and/or centrosome number.

PURPOSE: Normally fertilized zygotes generally show two pronuclei (2PN) and the extrusion of the second polar body. Conventional in vitro fertilization (c-IVF) and intracytoplasmic sperm injection (ICSI) often result in abnormal monopronuclear (1PN), tripronuclear (3PN), or other polypronuclear zygotes. In this study, we performed combined analyses of the methylation status of pronuclei (PN) and the number of centrosomes, to reveal the abnormal fertilization status in human zygotes. METHOD: We used differences in DNA methylation status (5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC)) to discriminate between male and female PN in human zygotes. These results were also used to analyze the centrosome number to indicate how many sperm entered into the oocyte. RESULT: Immunofluorescent analysis shows that all of the normal 2PN zygotes had one 5mC/5hmC double-positive PN and one 5mC-positive PN, whereas a parthenogenetically activated oocyte had only 5mC staining of the PN. All of the zygotes derived from ICSI (1PN, 3PN) had two centrosomes as did all of the 2PN zygotes derived from c-IVF. Of the 1PN zygotes derived from c-IVF, more than 50 % had staining for both 5mC and 5hmC in a single PN, and one or two centrosomes, indicating fertilization by a single sperm. Meanwhile, most of 3PN zygotes derived from c-IVF had a 5mC-positive PN and two 5mC/5hmC double-positive PNs, and had four or five centrosomes, suggesting polyspermy. CONCLUSIONS: We have established a reliable method to identify the PN origin based on the epigenetic status of the genome and have complemented these results by counting the centrosomes of zygotes.

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).

Possible mechanism of polyspermy block in human oocytes observed by time-lapse cinematography.

PURPOSE: To analyze the fertilization process related to polyspermy block in human oocytes using an in vitro culturing system for time-lapse cinematography. METHODS: We had 122 oocytes donated for this study from couples that provided informed consent. We recorded human oocytes at 2,000 to 2,800 frames every 10 s during the fertilization process and thereafter every 2 min using a new in vitro culture system originally developed by the authors for time-lapse cinematography. We displayed 30 frames per second for analysis of the polyspermy block during fertilization. RESULTS: Three oocytes showed the leading and following sperm within the zona pellucida in the same microscopic field. The dynamic images obtained during the fertilization process using this new system revealed that once a leading sperm penetrated the zona pellucida and attached to the oocyte membrane, a following sperm was arrested from further penetration into the zona pellucida within 10 s. CONCLUSIONS: The present results strongly suggest the existence of a novel mechanism of polyspermy block that takes place at the zona pellucida immediately after fertilization. These findings are clearly different from previous mechanisms describing polyspermy block as the oocyte membrane block to sperm penetration and the zona reaction. The finding presented herein thus represents a novel discovery about the highly complicated polyspermy block mechanism occurring in human oocytes.

Time-lapse cinematography of dynamic changes occurring during in vitro development of human embryos.

OBJECTIVE: The purpose of this study was to clarify developmental changes of early human embryos by using time-lapse cinematography (TLC). STUDY DESIGN: For human ova, fertilization and cleavage, development of the blastocyst, and hatching, as well as consequent changes were repeatedly photographed at intervals of 5-6 days by using an inverse microscope under stabilized temperature and pH. Photographs were taken at 30 frames per second and the movies were studied. RESULTS: Cinematography has increased our understanding of the morphologic mechanisms of fertilization, development, and behavior of early human embryos, and has identified the increased risk of monozygotic twin pregnancy based on prolonged incubation in vitro to the blastocyst stage. CONCLUSION: Using TLC, we observed the fertilization of an ovum by a single spermatozoon, followed by early cleavages, formation of the morula, blastocyst hatching, changes in the embryonic plates, and the development of monozygotic twins from the incubated blastocysts.

Age as a limiting factor for successful sperm retrieval in patients with nonmosaic Klinefelter's syndrome.

OBJECTIVE: To determine factors affecting successful sperm retrieval by testicular sperm extraction in patients with nonmosaic Klinefelter's syndrome. DESIGN: Medical record analysis for nonmosaic Klinefelter's syndrome patients who underwent testicular sperm extraction. SETTING: Three university-based tertiary centers. PATIENT(S): Fifty-one patients with nonobstructive azoospermia related to nonmosaic Klinefelter's syndrome. INTERVENTION(S): Testicular sperm extraction. MAIN OUTCOME MEASURE(S): Correlation of patient characteristics; serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T); as well as testicular volume with success in testicular sperm extraction. RESULT(S): We succeeded in obtaining spermatozoa in 26 patients and failed in 25. Levels of LH, FSH, and T and testicular volume did not differ between patient groups defined by success and failure. Median ages for successful and failed testicular sperm extraction were 31 and 38 years, respectively (statistically significant difference). When we analyzed success rates of testicular sperm extraction between two patient groups (<35 and > or =35 years old), the percentage of successful recovery of spermatozoa decreased after the age of 35 years (statistically significant difference). CONCLUSION(S): Testicular sperm extraction should be recommended before the critical age of 35 years.

Morphometric and cytogenetic characteristics of testicular germ cells and Sertoli cell secretory function in men with non-mosaic Klinefelter's syndrome.

BACKGROUND: Klinefelter's syndrome is the most frequent chromosomal abnormality in infertile men. In this study, the chromosomes of round spermatids and spermatogonia/primary spermatocytes from men with non-mosaic Klinefelter's syndrome were examined, together with the Sertoli cell secretory function and sperm morphometry. METHODS: Twenty-four men with non-mosaic Klinefelter's syndrome and nine men with obstructive azoospermia underwent therapeutic testicular biopsy. When spermatozoa in the final filtrate were present, they were processed for sperm morphometry or ICSI. Sperm morphometry was evaluated by the maximal length and width of the sperm head, the length of the midpiece and the ratio of the acrosomal region to the total surface area of the head. When round spermatids were present, they were processed for fluorescent in-situ hybridization (FISH). FISH was also applied to fragments of seminiferous tubules. Sertoli cell secretory function was measured by the amount of androgen binding protein (ABP) secreted in vitro. RESULTS: More than 93% of the evaluated round spermatids were normal. The proportions of 24,XY and of 24,XX round spermatids to the total number were significantly larger in men with Klinefelter's syndrome than in obstructed azoospermic men. Men with Klinefelter's syndrome who had spermatozoa in their testicular tissue (n = 12) were positive for both 46,XY and 47,XXY spermatogonia in their seminiferous tubules. In contrast, men with Klinefelter's syndrome without spermatozoa in their testicular tissue (n = 12) were positive for 47,XXY spermatogonia but negative for 46,XY spermatogonia in their seminiferous tubules. ABP profiles were significantly smaller in men with Klinefelter's syndrome who were negative for spermatozoa compared with men who were positive. Four pregnancies were achieved and five healthy babies were born. CONCLUSIONS: This study suggests that few 46,XXY spermatogonia undergo meiosis with an XX pairing and a Y univalent type of pairing. Hyperhaploid round spermatids (24,XY and 24,XX) may be produced by meiosis of 47,XXY spermatogonia. Men with Klinefelter's syndrome who are negative for testicular spermatozoa have a greater degree of Sertoli cell secretory dysfunction compared with men with Klinefelter's syndrome who are positive for spermatozoa. There are several defects in sperm morphometry with functional significance in men with Klinefelter's syndrome.