Evaluating Open and Closed Vitrification Systems: Impacts on Oocyte Competence and Cryopreservation Practices

Abstract:

Open and closed vitrification systems are commonly used for oocyte cryopreservation, but their impact on oocyte competence is not well understood. This study compares these systems, examining laboratory and clinical outcomes and the influence of cooling and warming rates. A systematic review of English-language studies up to January 2023 was conducted, involving 23 studies and a network meta-analysis. Both systems showed lower fertilization rates compared to fresh oocytes. Open systems had lower cleavage and blastocyst formation rates, while closed systems showed no significant difference. Closed systems appear less harmful to oocyte competence, suggesting their potential for standardization in practice

1. Introduction: Since the approval of oocyte vitrification in 2013, its use has increased significantly, replacing slow freezing due to superior outcomes. Vitrification, using ultrarapid cooling and high cryoprotectant concentrations, has applications in fertility preservation and donation programs. However, variations in protocols (e.g., open vs. closed systems) contribute to inconsistencies in results. Open systems offer ultrarapid freezing but risk contamination, while closed systems reduce contamination risk but may have slower cooling rates.
2. Methods: A systematic search of PubMed/MEDLINE and Cochrane Central Library databases identified 5,519 studies, narrowed to 23 based on inclusion criteria. Studies included prospective designs, focused on embryological (fertilization, cleavage, blastocyst rates) and clinical outcomes (pregnancy and live birth rates).
3. Results: The meta-analysis covered 27,204 oocytes. Open systems showed lower cleavage and blastocyst rates than fresh oocytes, while closed systems demonstrated similar outcomes to fresh. The cooling and warming rates of open systems may enhance developmental potential, but contamination concerns persist. Closed systems avoid contamination but may have slower cooling rates, impacting survival.
4. Discussion: The study highlights the importance of refining vitrification protocols to improve oocyte and embryo developmental competence. Open systems, while achieving higher cooling rates, may negatively influence oocyte dynamics due to direct contact with liquid nitrogen. Closed systems provide added safety against contamination and show improved blastocyst formation rates, supporting their potential for broader clinical adoption.
5. Conclusion The primary focus of cryopreservation is evolving beyond immediate clinical outcomes to encompass neonatal and adult health implications of offspring conceived using vitrified oocytes. This meta-analysis revealed that while open and closed systems perform similarly in clinical outcomes, closed systems exhibit advantages in safety and blastocyst formation rates. These findings, coupled with the closed system's reduced contamination risk, highlight its potential for standardization in cryopreservation practices. Further research should aim to clarify the biological effects of vitrification, focusing on understanding the mechanisms behind the differences observed between systems. Such efforts will guide the establishment of best practices, ensuring the safety and efficacy of cryopreservation as it continues to expand within assisted reproductive technologies.

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Source J Clin Med - PubMed