Search

Purpose: Recent evidence showed that the phase between pronuclear fading and the first cleavage is a perilous bridge connecting the zygote and the embryo. Indeed, delay in the short interval between pronuclear breakdown (PNBD) and the first cytokinesis may result in chromosome segregation errors. We tested the hypothesis that delays in this final phase of fertilization are associated with a detrimental impact on embryo development., Methods: This is a retrospective study of 1315 zygotes cultured using time lapse technologies generated in 205 first ICSI-cycles., Results: We observed an association between increasing times of the pronuclear fading-first cleavage interval (t2-tPNf) and the rates of trichotomous/direct unequal cleavage at the first (DUC-1) and second (DUC-2) mitotic cycle. Moreover, we observed a reduced blastulation rate. No significant associations were observed between rates of direct unequal cleavage at the third mitotic cycle (DUC-3) and top-quality blastocysts, euploidy, and live births. To evaluate whether the interval t2-tPNf could have a predictive value for the onset of DUC-1 and DUC-2, ROC curve analyses were performed. The area under the curve values obtained for DUC-1 showed a significant prediction accuracy. The best cut-offs to identify zygotes with a high risk of DUC-1 and DUC-2 occurrence were t2-tPNf > 2.78 (hours) and t2-tPNf > 2.50 (hours), respectively., Conclusion: Delay in the short interval between PNBD and the first cytokinesis result in trichotomous cleavage and early developmental arrest. However, if the embryos reach the blastocyst stage, rates of euploidy and live birth do not appear to be compromised., Competing Interests: Declarations. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Cell cycle regulation is crucial to assure expansion of a cell population, while preserving genome integrity. This notion is especially relevant to fertilization and early embryo development, a time when the cell cycle transforms from meiotic into mitotic cycles. Zygote-to-embryo transition is acutely error-prone, causing major developmental perturbations, including cleavage delays, tri- and multi-chotomous cleavages, and cell fragmentation. Another such alteration is bi- and multinucleation, consisting of the simultaneous formation of two or more nuclei at interphase. Indeed, multinucleation affects a large proportion of early human embryos, typically at the two-cell stage. Mechanistically, several factors, including spindle dysfunction, failed cleavage, and cell fusion, may generate this cell anomaly. In assisted reproduction treatment, multinucleation is associated with reduced developmental rates and lower implantation rates in Days 2-3 embryo transfers. However, many multinucleated embryos can develop to the blastocyst stage. In blastocyst transfers, the current evidence does not suggest a major impact of a previous history of multinucleation on the odds of euploidy or successful treatment outcomes. Human embryo multinucleation remains a not-fully-understood but developmentally relevant and intriguing phenomenon which requires further research of its generative mechanisms and clinical implications., (© The Author(s) 2024. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Purpose: To assess the relation between number of inseminated oocytes and cumulative live birth rate (CLBR) in order to provide guidance for limiting the number of surplus blastocysts., Methods: The study was a retrospective, single-center cohort analysis of 1223 ART complete cycles. Cycles were stratified according to female age (≤ 34, 35-38, and 39-42 years) and number of inseminated oocytes (1-5, 6-10, and > 10). Inclusion criteria were indication for IVF/ICSI with own spermatozoa and blastocyst culture up to day 6 of all embryos., Results: In patients younger than 35 years, insemination of more than ten oocytes produced an increase in overall blastocyst number, CLBR (40.3%, 54.3%, and 75.8%, respectively, for each oocyte group) and surplus embryo rate (12.9%, 27.8%, and 49.7% of cases for each group). Instead, in the middle age group, the use of more than ten oocytes was solely associated with an increase in the rate of surplus embryos (1.25%, 21.33%, and 28.68% of cases after stratification for oocyte number). In older patients, neither CLBR (9.1%, 23.9%, and 24.7%, respectively) nor rate of surplus embryos (2.0%, 7.1%, and 13.4% of cases for each group) were higher in cycles with more than ten inseminated oocytes., Conclusion: In women up to 38 years, sustainable CLBR are achieved while limiting the number of inseminated oocytes and the resulting blastocysts remaining unused. Based on this notion, novel treatment strategies could pursue high outcome rates, while alleviating the problems derived from surplus stored embryos., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Study Question: What clinical and laboratory differences emerge from parallel direct comparison of embryos reaching the blastocyst stage between Days 4, 5, 6, and 7 (Days 4-7)?, Summary Answer: Increasing times to blastocyst formation are associated with a worse clinical outcome and perturbations in developmental patterns appear as early as the fertilization stage., What Is Known Already: Previous evidence indicates that later times to blastocyst development are associated with a worse clinical outcome. However, the vast majority of these data concern Day 5 and Day 6 blastocysts, while Day 4 and Day 7 blastocysts remain less thoroughly investigated. In addition, studies comparing in parallel the developmental patterns and trajectories of Day 4-7 blastocysts are lacking. This leaves unanswered the question of when and how differences among such embryos emerge. Acquisition of such knowledge would significantly contribute to understanding the relative impact of intrinsic and extrinsic causes of embryo developmental kinetics and competence., Study Design, Size, Duration: This retrospective study involved time-lapse technology (TLT) monitoring of Day 4 (N = 70), Day 5 (N = 6147), Day 6 (N = 3243), and Day 7 (N = 149) blastocysts generated in 9450 ICSI cycles. Oocyte retrievals were carried out after clomiphene citrate-based minimal ovarian stimulation, between January 2020 and April 2021., Participants/materials, Setting, Methods: Couples included in the study presented with different diagnoses, mainly male factor and unexplained infertility. Cases involving cryopreserved gametes or surgically retrieved sperm were excluded. Microinjected oocytes were assessed by a combined TLT-culture system. Day 4-7 blastocyst groups were compared in terms of morphokinetics (pronuclear dynamics, cleavage patterns and timings, and embryo quality) and clinical outcome. Clinically usable blastocysts were cryopreserved and transferred in single vitrified-warmed blastocyst transfers (SVBT)., Main Results and the Role of Chance: From 19 846 microinjected oocytes, 17 144 zygotes (86.4%) were obtained. Overall, the blastocyst development rate was 56.0%. Rates of blastocysts formation on Days 4, 5, 6, and 7 were 0.7%, 64.0%, 33.8%, and 1.6%, respectively. The average expanded blastocyst development times were 98.4 ± 0.4, 112.4 ± 0.1, 131.6 ± 0.1, and 151.2 ± 0.5 h in the Day 4-7 groups, respectively. Female age was positively associated with longer times to blastocyst development. Rates of both inner cell mass (ICM) and trophectoderm (TE) morphological grade A blastocysts were negatively associated with the day of blastocyst development (P < 0.0001). The differences in development times and intervals increased progressively until blastocyst expansion (P < 0.0001 for all development times). Strikingly, such differences were already markedly evident as early as the time of pronuclear fading (tPNf) (20.6 ± 0.3, 22.5 ± 0.0, 24.0 ± 0.0, 25.5 ± 0.3; Days 4-7, respectively; P < 0.0001). Rates of cleavage anomalies (tri-/multi-chotomous mitosis or rapid cleavage) occurring at the first or second/third division cycles were also positively associated with longer times to blastocyst development. Implantation, ongoing pregnancy, and live birth rates were progressively reduced with increasing blastocyst development times (P < 0.0001), even after stratification for maternal age. When controlled for female age, male age, number of previous embryo transfer cycles, morphological grade of the ICM and TE, and progesterone supplementation, the probabilities of implantation, clinical, and ongoing pregnancy and live birth were significantly decreased in Day 6 blastocysts in comparison to Day 5 blastocysts. Follow-up data on birth length, weight, and malformations were comparable among the four blastocyst groups., Limitations, Reasons for Caution: The study is limited by its retrospective design. Having been obtained from a single centre, the data require independent validation., Wider Implications of the Findings: This study extends previous data on the relation between time of blastocyst formation and clinical outcome. It also indicates that differences in developmental times and patterns of Day 4-7 blastocysts occur as early as the fertilization stage, possibly dictated by intrinsic gamete-derived factors., Study Funding/competing Interest(s): This study was supported by the participating institutions. The authors have no conflict of interest to declare., Trial Registration Number: N/A., (© The Author(s) 2023. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Purpose: To investigate whether high relative humidity conditions (HC), when using a time-lapse system (TLS) with sequential culture media, are beneficial to embryo culture, improving ongoing pregnancy rates., Methods: We included patients undergoing their first ICSI cycle treatment from April 2021 to May 2022. Patients assigned to dry conditions (DC) or HC were 278 and 218, respectively. We used a GERI TLS, three chambers configured in humidity conditions and three in dry conditions. The effect of HC on ongoing pregnancy rate was assessed by the propensity matched sample, to reduce potential differences between women undergoing either HC or DC and reduce biased estimation of treatment effect., Result: After adjusting for several confounding variables and applying the propensity score (PS), no significant differences were observed in the rates of normal (2PN) and abnormal (1PN and 3PN) fertilization, blastulation, top-quality blastocysts, frozen blastocysts, ongoing pregnancies, and miscarriages. The 2-cell (t2) and 4-cell (t4) stages and cell divisions between such stages occurred earlier and were more synchronous in the in DC., Conclusion: These results suggest that HC conditions do not improve the rate of ongoing pregnancy and several embryological outcomes, under the conditions used in this study based on a time-lapse system and sequential culture with day 3 medium change-over., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Purpose: To test the validity of the Vienna consensus laboratory key performance indicators (KPIs) to monitor the outcome of treatments involving women of different age ranges., Methods: The retrospective cohort study included 862 complete IVF/ICSI cycles carried out between January 2014 and May 2021. All embryos of each cycle cohort were subject to extended culture. The overall population was divided into two groups according to female age: the Vienna consensus (≤ 39 years) and older female age (≥ 40 years). We compared outcomes of a selection of the Vienna performance indicators (PIs) and KPIs, with a focus on measures relevant to embryo cleavage and blastocyst formation. A possible association between total good blastocyst development rate (TGBDR) and cumulative clinical pregnancy rate (CPR) was also assessed., Results: No differences were observed in fertilization and embryo cleavage KPIs between the Vienna consensus and the older female age group (standard IVF fertilization, 67.2 vs. 67.3; ICSI fertilization, 72.3 vs. 75.3; day 2 development, 57.6% vs 58.7%; day 3 development, 52.4% vs. 50.7%, respectively). TGBDR was lower in the older female age group (45.5% vs. 33.4% p < 0.001). Multivariate logistic regression analysis indicated female age as a factor independently associated with TGBDR. Clinical outcomes significantly decreased with increasing female age., Conclusion: The study suggests that, while most laboratory outcome measures are reliably applicable irrespective of female age, KPIs describing extended embryo culture should be fine-tuned in consideration of older female age., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)