Open versus closed systems for vitrification of human oocytes and embryos

A compact, high-throughput semi-automated embryo vitrification system based on hydrogel

RESEARCH QUESTION

What is the efficiency and efficacy of the novel Biorocks semi-automated vitrification system, which is based on a hydrogel?

DESIGN

This comparative experimental laboratory study used mouse model and human day 6 blastocysts. Mouse oocytes and embryos were quality assessed post-vitrification.

RESULTS

The Biorocks system successfully automated the solution exchanges during the vitrification process, achieving a significantly improved throughput of up to 36 embryos/oocytes per hour. Using hydrogel for cryoprotective agent delivery, 12 vessels could be processed simultaneously, fitting comfortably within an assisted reproductive technology (ART) workstation. In tests involving the cryopreservation of oocytes and embryos, the system yielded outcomes equivalent to the manual Cryotop method. For example, the survival rate for mouse oocytes was 98% with the Biorocks vitrification system (n = 46) and 95% for the manual Cryotop method (n = 39), of which 46% and 41%, respectively, progressed to blastocysts on day 5 after IVF. CC-grade day 6 human blastocysts processed with the Biorocks system (n = 39) were associated with a 92% 2 h re-expansion rate, equivalent to the 90% with Cryotop (n = 30). The cooling/warming rates achieved by the Biorocks system were 31,900°C/minute and 24,700°C/minute, respectively. Oocyte quality was comparable or better post-vitrification for Biorocks than Cryotop.

CONCLUSIONS

The Biorocks semi-automated vitrification system offers enhanced throughput without compromising the survival and developmental potential of oocytes and embryos. This innovative system may help to increase the efficiency and standardization of vitrification in ART clinics. Further investigations are needed to confirm its efficacy in a broader clinical context.

The Effect of Open and Closed Oocyte Vitrification Systems on Embryo Development: A Systematic Review and Network Meta-Analysis

Background/Objectives: Open and closed vitrification systems are commonly employed in oocyte cryopreservation; however, there is limited evidence regarding a comparison of their separate impact on oocyte competence. This study uniquely brings to the literature, data on the effect of open versus closed vitrification systems on laboratory and clinical outcomes, and the effect of cooling and warming rates. Methods: A systematic search of the literature was performed using the databases PubMed/MEDLINE and the Cochrane Central Library, limited to articles published in English up to January 2023. A network meta-analysis was conducted comparing each vitrification system versus fresh oocytes. Results: Twenty-three studies were included. When compared to fresh oocytes, both vitrification devices resulted in lower fertilization rates per MII oocyte retrieved. When comparing the two systems in terms of survival rates, no statistically significant difference was observed. However, interestingly open systems resulted in lower cleavage and blastocyst formation rates per 2 pronuclear (2PN) oocyte compared to fresh controls, while at the same time no statistically significant difference was detected when comparing closed devices with fresh oocytes. Conclusions: In conclusion, closed vitrification systems appear to exert a less detrimental impact on the oocytes' competence, which is reflected in the blastocyst formation rates. Proof of superiority of one system versus the other may lead to standardization, helping to ultimately determine optimal practice in oocyte vitrification.

Effect of post-vitrification cryopreservation duration on singleton birth-weight in frozen-thawed blastocysts transfer cycles

Introduction

This study aimed to explore the effect of cryopreservation duration after blastocyst vitrification on the singleton birth-weight of newborns to assess the safety of long-term preservation of frozen-thawed blastocyst transfer (FBT) cycles.

Methods

This was a retrospective observational study conducted at the Gynecological Endocrinology and Assisted Reproduction Center of the Peking Union Medical College Hospital. Patients who gave birth to singletons between January 2006 and December 2021 after undergoing FBT cycles were included. Five groups were formed according to the duration of cryopreservation of embryos at FBT: Group I included 274 patients with a storage time < 3 months. Group II included 607 patients with a storage time of 3-6 months. Group III included 322 patients with a storage time of 6-12 months. Group IV included 190 patients with a storage time of 12-24 months. Group V included 118 patients with a storage time of > 24 months. Neonatal outcomes were compared among the groups. Multivariate linear regression analysis was performed to evaluate birth-weights and other birth-related outcomes.

Results

A total of 1,511 patients were included in the analysis. The longest cryopreservation period was 12 years. The birth-weights of neonates in the five groups were 3344.1 ± 529.3, 3326.1 ± 565.7, 3260.3 ± 584.1, 3349.9 ± 582.7, and 3296.7 ± 491.9 g, respectively (P > 0.05). The incidences of preterm birth, very preterm birth, low birth-weight, and very low birth-weight were similar in all groups (P > 0.05). The large-for-gestational-age and small-for-gestational-age rates did not differ significantly among the groups (P > 0.05). After adjusting for confounding factors that may affect neonatal outcomes, a trend for an increased risk of low birth-weight with prolonged cryopreservation was observed. However, cryopreservation duration and neonatal birth-weight were not significantly correlated (P > 0.05).

Conclusion

The duration of cryopreservation after blastocyst vitrification with an open device for more than 2 years had no significant effect on the birth-weight of FBT singletons; however, attention should be paid to a possible increase in the risk of low birth-weight.

Review of human oocyte cryopreservation in ART programs: Current challenges and opportunities

Oocyte cryopreservation has notably increased in recent times, to become an essential part of clinical infertility treatment. Since the 1980s, many improvements in oocyte cryopreservation (OC) have been adopted, including the great advance with the application of vitrification. The commonly used vitrification protocol applies different cryoprotectants (Ethylene glycol and/or DMSO and/or PROH and sucrose and/or Trehalose) and two different steps: firstly, exposure in equilibration solution for 5-15 min, followed by a vitrification solution for 60-90 s at room temperature. The warming method includes a first step for 1 min at 37 °C and 3 subsequent steps at room temperature to remove the cryoprotectant for a total of 9-12 min. In addition, biosafety is a critical aspect to mention, and it is related to devices used during the vitrification, mainly in terms of whether the biological vitrified material comes in direct contact with liquid nitrogen (open vitrification) or not (closed vitrification), where LN2 may contain potentially contaminating viruses or pathogens. Furthermore, during early development major waves of epigenetic reprogramming take place. Recent literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by vitrification, including osmotic shock, temperature, rapid changes of pH and toxicity of cryoprotectants. It is, therefore, important to better understand the potential perturbations of epigenetic modifications that may be associated with the globally used vitrification methods. Therefore, we here discuss the benefits and efficiency of human oocyte vitrification; we also review the evidence surrounding oocyte cryopreservation-related epigenetic modifications and potential epigenetic dysregulations, together with long-term consequences for offspring health.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

The international transportation of frozen embryos does not affect IVF outcomes

PURPOSE

The regulated transportation of cryopreserved human embryos resulting from assisted reproduction treatments offers opportunities for patients undergoing embryo transfer in other regions/countries. However, the principal concern for fertility clinics is maintaining unaltered embryo quality to ensure satisfactory clinical outcomes. The aim of the study was to evaluate the efficacy of the transportation process comparing the survival rate and competence of transported embryos to embryos produced and transferred on-site, in frozen embryo transfer cycles.

METHODS

This retrospective study assessed the outcomes of 621 blastocysts thawed at IVI Roma (Italy) between March 2021 and March 2022. Autologous or donated oocytes fertilized in vitro, cultured to the blastocyst stage, and cryopreserved in IVI Roma clinic (Group A, n = 450), were compared to embryos generated in IVI Spain clinics and transported to IVI Roma (Group B, n = 171).

RESULTS

Groups A and B respectively showed no significant difference in embryo survival rates after thawing (N = 440/450, 97.8% vs. N = 168/171, 98.2%, p = 0.71), pregnancy rates (N = 221/440, 50.23% vs. N = 77/168, 45.83%, p = 0.33), clinical pregnancy rates (N = 200/440, 45.45% vs. N = 62/168, 36.90%, p = 0.06), and miscarriage rates (N = 42/221, 19,00% vs. 21/77, 28.57%, p = 0.13), even after stratification for the source of the oocyte. Logistic binomial regression considering donor oocytes, preimplantation genetic testing, and patients' age, did not show any significant results on embryo survival and IVF outcomes.

CONCLUSION

The regulated transport of cryopreserved blastocysts did not affect embryo survival rate or IVF outcomes. Our data support the safety of embryo cryopreservation and medical transportation services, allowing clinics and patients to transport embryos with no significant risk to embryo competence.

Cryostorage management of reproductive cells and tissues in ART: status, needs, opportunities and potential new challenges

Among the wide range of procedures performed by clinical embryologists, the cryopreservation of reproductive cells and tissues represents a fundamental task in the daily routine. Indeed, cryopreservation procedures can be considered a subspecialty of medically assisted reproductive technology (ART), having the same relevance as sperm injection or embryo biopsy for preimplantation genetic testing. However, although a great deal of care has been devoted to optimizing cryopreservation protocols, the same energy has only recently been spent on developing and implementing strategies for the safe and reliable storage and transport of reproductive specimens. Herein, we have summarized the content of the available guidelines, the risks, the needs and the future perspectives regarding the management of cryopreservation biorepositories used in ART.

Different Impacts of Cryopreservation in Endothelial and Epithelial Ovarian Cells

The aim of our laboratory-based study was to investigate the extent of delayed-onset cell death after cryopreservation in endothelial and epithelial cell lines of ovarian origin. We found differences in percentages of vital cells directly after warming and after cultivation for 48 to 72 h. A granulosa cell line of endothelial origin (KGN) and an epithelial cell line (OvCar-3) were used. In both DMSO-containing and DMSO-free protocols, significant differences in vitality rates between the different cell lines when using open and closed vitrification could be shown (DMSO-containing: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.001; DMSO-free: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.031). Furthermore, there was a marked difference in the percentage of vital cells immediately after warming and after cultivation for 48 to 72 h; whereas the KGN cell line showed a loss of cell viability of 41% using a DMSO-containing protocol, the OvCar-3 cell loss was only 11% after cultivation. Using a DMSO-free protocol, the percentages of late-onset cell death were 77% and 48% for KGN and OvCar-3 cells, respectively. Our data support the hypothesis that cryopreservation-induced damage is cell type and cryoprotective agent dependent.

A comprehensive review and update on human fertility cryopreservation methods and tools

The broad conceptualization of fertility preservation and restoration has become already a major concern in the modern western world since a large number of individuals often face it in the everyday life. Driven by different health conditions and/or social reasons, a variety of patients currently rely on routinely and non-routinely applied assisted reproductive technologies, and mostly on the possibility to cryopreserve gametes and/or gonadal tissues for expanding their reproductive lifespan. This review embraces the data present in human-focused literature regarding the up-to-date methodologies and tools contemporarily applied in IVF laboratories' clinical setting of the oocyte, sperm, and embryo cryopreservation and explores the latest news and issues related to the optimization of methods used in ovarian and testicular tissue cryopreservation.

Effect of interval between oocyte retrieval and resuscitation embryo transfer on pregnancy outcomes

Objectives

Resuscitation transfer of embryos after elective cryopreservation has been widely applied in in vitro fertilization-embryo transfer (IVF-ET) therapy for human infertility or sterility owing to higher embryo implantation rates. This method separates oocyte retrieval from embryo transfer. The optimal time for frozen embryo transfer (FET) remains unknown. Therefore, this study mainly compares the advantages and disadvantages of delayed FET and immediate FET through retrospective analysis.

Methods

We analyzed real world data of patients who underwent resuscitation transplantation between October 2019 and July 2021 at the Reproductive Center of Chengdu Jinjiang Hospital for Women's and Children's Health. Propensity score matching was applied to control potential confounding factors. A total of 5,549 patients who received at least one FET were analyzed. Patients undergoing transplantation within 60 days of oocyte retrieval were included in the immediate FET group (n = 1,265) and those undergoing transplantation > 60 days after retrieval were included in the delayed FET group (n = 4,284).

Results

Live birth rates between the two groups were comparable (45.25% vs. 45.76%, p = 0.757). Moreover, no difference was observed in the rates of biochemical pregnancy (64.50% vs. 66.80%), clinical pregnancy (55.24% vs. 56.83%), ectopic pregnancy (1.47% vs. 1.39%), early miscarriage (14.41% vs. 16.20%), late miscarriage (2.21% vs. 2.09%), singleton premature delivery (16.67% vs. 18.29%), and neonatal deformity (1.97% vs. 1.80%). After stratifying the patients based on the type of embryo transferred, number of embryos transferred, FET protocol, and good prognosis criteria, live birth rates remained comparable between the two groups (p > 0.05).

Conclusion

Pregnancy outcomes were comparable between the immediate and delayed FET groups.

High pressure frozen oocytes have improved ultrastructure but reduced cleavage rates compared to conventionally fixed or vitrified oocytes

Context Live birth rates are lower for cryopreserved oocytes than for fresh IVF cycles, indicating a need for improved methodologies. Aims The aim of this study was to determine if high pressure freezing (HPF) could improve both ultrastructural preservation and cryopreserved oocyte quality when compared to conventional fixation and vitrification methods. Methods Sheep oocytes and embryos were prepared by HPF or vitrification, with or without cryoprotectants. Frozen oocytes were prepared for transmission electron microscopy or warmed, in vitro fertilised and the recovery and cleavage rates recorded. Key results Blastocyst rates were similar between fresh, HPF and vitrified embryos. HPF oocytes had improved ultrastructure compared to conventional fixation or vitrification, but had poorer survival and cleavage rates compared to vitrified oocytes. Freeze-substitution of cryopreserved oocytes and transmission electron microscopy demonstrated disruption of the oocyte ultrastructure in the presence of cryoprotectants. Conclusions Superior preservation of ultrastructure was observed in HPF oocytes compared to vitrification or conventional fixation methods. In the presence of CP, both embryos and oocytes could survive HPF and warming but oocytes had reduced development. Implications The HPF method has potential to be developed and lead to improved oocyte and embryo cryopreservation and outcomes for assisted reproduction.

Ultrastructural Evaluation of the Human Oocyte at the Germinal Vesicle Stage during the Application of Assisted Reproductive Technologies

After its discovery in 1825 by the physiologist J.E. Purkinje, the human germinal vesicle (GV) attracted the interest of scientists. Discarded after laparotomy or laparoscopic ovum pick up from the pool of retrieved mature oocytes, the leftover GV was mainly used for research purposes. After the discovery of Assisted Reproductive Technologies (ARTs) such as in vitro maturation (IVM), in vitro fertilization and embryo transfer (IVF-ET) and intracytoplasmic sperm injection (ICSI), its developing potential was explored, and recognized as an important source of germ cells, especially in the case of scarce availability of mature oocytes for pathological/clinical conditions or in the case of previous recurrent implantation failure. We here review the ultrastructural data available on GV-stage human oocytes and their application to ARTs.

Relevance of Aquaporins for Gamete Function and Cryopreservation

Simple Summary

The interaction between cells and the extracellular medium is of great importance; changes in medium composition can drive water movement across plasma membranes. Aquaporins (AQPs) are membrane channels involved in the transport of water and some solutes across membranes. When sperm enter the female reproductive tract after ejaculation, they encounter a drastic change in extracellular composition, which leads to water flowing across the plasma membrane. This triggers a series of events that are crucial to allowing fertilization to take place, such as regulation of sperm motility. In the context of assisted reproduction techniques (ART), long-term storage of gametes is sometimes required, and, during cryopreservation, these cells undergo drastic changes in extracellular medium composition. As a result, AQPs are crucial in both sperm and oocytes during this process. Cryopreservation is of considerable importance for fertility preservation in livestock, endangered species and for individuals undergoing certain medical treatments that compromise their fertility. Further research to fully elucidate the roles and underlying mechanisms of AQPs in mammalian sperm is therefore warranted.

Abstract

The interaction between cells and the extracellular medium is of great importance, and drastic changes in extracellular solute concentrations drive water movement across the plasma membrane. Aquaporins (AQPs) are a family of transmembrane channels that allow the transport of water and small solutes across cell membranes. Different members of this family have been identified in gametes. In sperm, they are relevant to osmoadaptation after entering the female reproductive tract, which is crucial for sperm motility activation and capacitation and, thus, for their fertilizing ability. In addition, they are relevant during the cryopreservation process, since some members of this family are also permeable to glycerol, one of the most frequently used cryoprotective agents in livestock. Regarding oocytes, AQPs are very important in their maturation but also during cryopreservation. Further research to define the exact sets of AQPs that are present in oocytes from different species is needed, since the available literature envisages certain AQPs and their roles but does not provide complete information on the whole set of AQPs. This is of considerable importance because, in sperm, specific AQPs are known to compensate the role of non-functional members.

An expert commentary on essential equipment, supplies and culture media in the ART laboratory

The ART laboratory is a complex system designed to sustain the fertilization, survival, and culture of the preimplantation embryo to the blastocyst stage. ART outcomes depend on numerous factors, among which are the equipment, supplies and culture media used. The number and type of incubators also may affect ART results. While large incubators may be more suitable for media equilibration, bench-top incubators may provide better embryo culture conditions in separate or smaller chambers and may be coupled with time-lapse systems that allow continuous embryo monitoring. Microscopes are essential for observation, assessment, and micromanipulation. Workstations provide a controlled environment for gamete and embryo handling and their quantity should be adjusted according to the number of ART cycles treated in order to provide a steady and efficient workflow. Continuous maintenance, quality control and monitoring of equipment is essential and quality control devices such as the thermometer, and pH-meter are necessary to maintain optimal culture conditions. Tracking, appropriate delivery and storage conditions, and quality control of all consumables is recommended so that the adequate quantity and quality is available for use. Embryo culture media have evolved: preimplantation embryos are cultured either by sequential media or single-step media that can be used for interrupted or uninterrupted culture. There is currently no sufficient evidence that any individual commercially-available culture system is better than others in terms of embryo viability. In this review, we aim to analyse the various parameters that should be taken into account when choosing the essential equipment, consumables and culture media systems that will create optimal culture conditions and provide the most effective patient treatment.

Semi-automated versus manual embryo vitrification: inter-operator variability, time-saving, and clinical outcomes

PURPOSE

Does semi-automated vitrification have lower inter-operator variability and better clinical outcomes than manual vitrification?

METHODS

Retrospective analyses of 282 patients whose embryos had been cryopreserved, manually with Irvine®-CBS® (MV) or semi-automatically vitrified with the GAVI® method (AV) (from November 2017 to September 2020). Both techniques were performed during the same period by 5 operators. Inter-operator variability was statistically analyzed between operators who performed the vitrification and those who performed the warming process to compare the intact survival rate (% embryos with 100% intact blastomeres) and the positive survival rate (at least 50% intact blastomeres). Additionally, the complete vitrification time was assessed for the 2 techniques according to the number of vitrified embryos.

RESULTS

Manual vitrification involved warming 338 embryos in 266 cycles for 181 couples compared to 212 embryos in 162 AV cycles for 101 patients. The positive survival rate was higher (p < 0.05) after MV (96%; 323/338) than after AV (90%; 191/212). The intact survival rate (86 vs 84%) and the clinical pregnancy rate (27 vs 22%) were not significantly different between MV and AV. Regarding the inter-operator variability, no significant difference in positive and intact survival rate was evident between the 5 technicians, neither by vitrification nor by warming steps with MV and AV. Concerning time-saving, the MV technique proved to be quicker than AV (minus 11 ± 9 min).

CONCLUSIONS

Manual vitrification exhibited favorable total survival rates and was more time efficient, while both MV and AV cooling and warming treatments showed little operator variability.

ISAR Consensus Guidelines on Add-Ons Treatment in In vitro Fertilization

STUDY QUESTION

What are the good practices for the use of ADD-ON Treatments in IVF cycles in INDIA?

WHAT IS ALREADY KNOWN

Add on treatments in IVF are procedures and technologies which are offered to patients in hope of improving the success rates. A lot of add on treatments exist; most of them have limited evidence and data for the Indian patient population is miniscule. These interventions may have limited effects, so it is imperative that any new technology that is offered is evaluated properly and has enough evidence to suggest that it is safe and effective.

STUDY DESIGN SIZE DURATION

This is the report of a 2-day consensus meeting where two moderators were assigned to a group of experts to collate information on Add on treatments in IVF in INDIA. This meeting utilised surveys, available scientific evidence and personal laboratory experience into various presentations by experts on pre-decided specific topics.

PARTICIPANTS/MATERIALS SETTING METHODS

Expert professionals from ISAR representing clinical and embryology fields.

MAIN RESULTS AND THE ROLE OF CHANCE

The report is divided in various components including the health of the Offspring, the various ADD ons available to an ART center, consensus points for each technology & qualifications and trainings for embryologists, the report and recommendations of the expert panel reflect the discussion on each of the topics and try to lay down good practice points for labs to follow.

LIMITATIONS REASONS FOR CAUTION

The recommendations are solely based on expert opinion. Future availability of data may warrant an update of the same.

WIDER IMPLICATIONS OF THE FINDINGS

These guidelines can help labs across the country to standardise their ART services and improve clinical outcomes, it will also motivate clinics to collect data and report the use of Add ons to the national registry.

STUDY FUNDING/COMPETING INTERESTS

The consensus meeting and writing of the paper was supported by funds from CooperSurgical India.

Vitrifying multiple embryos in different arrangements does not alter the cooling rate

Vitrification is the most common method of cryopreservation of gametes in fertility clinics due to its improved survival rates compared to slow freezing techniques. For the Open Cryotop® vitrification device, the number of oocytes, or embryos, mounted onto a single device can vary. In this work, a mathematical model is developed for the cooling of oocytes and embryos (samples). The model is solved computationally, to investigate whether varying the number of samples mounted onto the Open Cryotop® affects the cooling rates, and consequently the survival rates, of vitrified samples. Several realistic spatial arrangements of samples are examined, determining their temperature over time. In this way we quantify the effect of spatial arrangement on the cooling rate. Our results indicate that neither the spatial arrangement nor the number of mounted samples has a large effect on cooling rates, so long as the volume of the cryoprotectant remains minimal. The time taken for cooling is found to be on the order of half a second, or less, regardless of the spatial arrangement or number of mounted samples. Hence, rapid cooling can be achieved for any number or arrangement of samples, as long as device manufacturer guidelines are adhered to.

Microbial occurrence in liquid nitrogen storage tanks: a challenge for cryobanking?

Abstract

Modern biobanks maintain valuable living materials for medical diagnostics, reproduction medicine, and conservation purposes. To guarantee high quality during long-term storage and to avoid metabolic activities, cryostorage is often conducted in the N₂ vapour phase or in liquid nitrogen (LN) at temperatures below − 150 °C. One potential risk of cryostorage is microbial cross contamination in the LN storage tanks. The current review summarises data on the occurrence of microorganisms that may compromise the safety and quality of biological materials during long-term storage. We assess the potential for the microbial contamination of LN in storage tanks holding different biological materials based on the detection by culture-based and molecular approaches. The samples themselves, the LN, the human microbiome, and the surrounding environment are possible routes of contamination and can cause cross contaminations via the LN phase. In general, the results showed that LN is typically not the source of major contaminations and only a few studies provided evidence for a risk of microbial cross contamination. So far, culture-based and culture-independent techniques detected only low amounts of microbial cells, indicating that cross contamination may occur at a very low frequency. To further minimise the potential risk of microbial cross contaminations, we recommend reducing the formation of ice crystals in cryotanks that can entrap environmental microorganisms and using sealed or second sample packing. A short survey demonstrated the awareness for microbial contaminations of storage containers among different culture collections. Although most participants consider the risk of cross contaminations in LN storage tanks as low, they prevent potential contaminations by using sealed devices and − 150 °C freezers. It is concluded that the overall risk for cross contaminations in biobanks is relatively low when following standard operating procedures (SOPs). We evaluated the potential sources in detail and summarised our results in a risk assessment spreadsheet which can be used for the quality management of biobanks.

Key points

• Identification of potential contaminants and their sources in LN storage tanks.

• Recommendations to reduce this risk of LN storage tank contamination.

• Development of a risk assessment spreadsheet to support quality management.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11531-4.

A randomised, multi-center, open trial comparing a semi-automated closed vitrification system with a manual open system in women undergoing IVF

STUDY QUESTION

What are outcome and procedural differences when using the semi-automated closed Gavi® device versus the manual open Cryotop® method for vitrification of pronuclear (2PN) stage oocytes within an IVF program?

SUMMARY ANSWER

A semi-automated closed vitrification method gives similar clinical results as compared to an exclusively manual, open system but higher procedure duration and less staff convenience.

WHAT IS KNOWN ALREADY

A semi-automated closed vitrification device has been introduced to the market, however, little evaluation of its performance in a clinical setting has been conducted so far.

STUDY DESIGN, SIZE, DURATION

This prospective, randomised, open non-inferiority trial was conducted at three German IVF centers (10/2017-12/2018). Randomization was performed on day of fertilization check, stratified by center and by indication for vitrification (surplus 2PN oocytes in the context of a fresh embryo transfer (ET) cycle or 'freeze-all' of 2PN oocytes).

PARTICIPANT/MATERIAL, SETTING, METHODS

The study population included subfertile women, aged 18-40 years, undergoing IVF or ICSI treatment after ovarian stimulation, with 2PN oocytes available for vitrification. The primary outcome was survival rate of 2PN oocytes at first warming procedure in a subsequent cycle and non-inferiority of 2PN survival was to be declared if the lower bound 95% CI of the mean difference in survival rate excluded a difference larger than 9.5%; secondary, descriptive outcomes included embryo development, pregnancy and live birth rate, procedure time and staff convenience.

MAIN RESULTS AND THE ROLE OF CHANCE

The randomised patient population consisted of 149 patients, and the per-protocol population (patients with warming of 2PN oocytes for culture and planned ET) was 118 patients. The survival rate was 94.0% (±13.5) and 96.7% (±9.7) in the Gavi® and the Cryotop® group (weighted mean difference -1.6%, 95% CI -4.7 to 1.4, P = 0.28), respectively, indicating non-inferiority of the Gavi® vitrification/warming method for the primary outcome. Embryo development and the proportion of top-quality embryos was similar in the two groups, as were the pregnancy and live birth rate. Mean total procedure duration (vitrification and warming) was higher in the Gavi® group (81 ± 39 min vs 47 ± 15 min, mean difference 34 min, 95% CI 19 to 48). Staff convenience assessed by eight operators in a questionnaire was lower for the Gavi® system. The majority of respondents preferred the Cryotop® method because of practicality issues.

LIMITATIONS, REASON FOR CAUTION

The study was performed in centers with long experience of manual vitrification, and the relative performance of the Gavi® system as well as the staff convenience may be higher in settings with less experience in the manual procedure. Financial costs of the two procedures were not measured along the trial.

WIDER IMPLICATIONS OF THE FINDINGS

With increasing requirements for standardization of procedures and tissue safety, a semi-automated closed vitrification method may constitute a suitable alternative technology to the established manual open vitrification method given the equivalent clinical outcomes demonstrated herein.

STUDY FUNDING/COMPETING INTERESTS

The trial received no direct financial funding. The Gavi® instrument, Gavi® consumables and staff training were provided for free by the distributor (Merck, Darmstadt, Germany) during the study period. The manufacturer of the Gavi® instrument had no influence on study protocol, study conduct, data analysis, data interpretation or manuscript writing. J.H. has received honoraria and/or non-financial support from Ferring, Merck and Origio. G.G. has received honoraria and/or non-financial support from Abbott, Ferring, Finox, Gedeon Richter, Guerbet, Merck, MSD, ObsEva, PregLem, ReprodWissen GmbH and Theramex. The remaining authors have no competing interests.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT03287479.

TRIAL REGISTRATION DATE

19 September 2017.

DATE OF FIRST PATIENT’S ENROLMENT

10 October 2017.

"Comparison of two closed vitrification methods for vitrifying dromedary camel (Camelus dromedarius) embryos"

A total of 184 dromedary camel embryos were vitrified using a novel vitrification kit specifically developed for camel embryos. These embryos were vitrified using a 3-step process by exposing them to vitrification solutions (VS) containing 20% foetal calf serum (FCS) with (+) or without (-) the addition of bovine serum albumin (BSA). Embryos were then further divided into two groups (<or ≥ 500 μm), vitrified using a closed vitrification system and stored on a Cryolock® embryo storage device or vitrified using solid surface vitrification of the Cryologic Vitrification Method (CVM)™ and stored on a Fibreplug™ embryo storage device. Embryos were then warmed and transferred in pairs, of approximately equal size, into recipient camels on Day 6 after ovulation. A total of 92 embryos were vitrified using the Cryolock; 86 embryos (C-BSA, n = 46; C + BSA, n = 40) survived warming, and were then transferred into 43 recipients. The pregnancy rate (PR) per recipient was 17% (C-BSA: 4/23) and 45% (C + BSA: 9/20) at 20 days after transfer but reduced to 9% and 30% at 60 days of gestation, respectively. For the Fibreplug group, a total of 92 embryos were vitrified, 86 embryos (F-BSA, n = 44; F + BSA, n = 42) survived warming, and were transferred into 43 recipients. The PR per recipient was 73% (F-BSA: 16/22) and 48% (F + BSA: 10/21) at 20 days after transfer but reduced to 50% (11/22) and 33% (7/21) at 60 days of gestation, respectively. Of the 39 pregnancies at 20 days after transfer, 77% (30/39) resulted from embryos with a diameter of 300-450 μm and 23% (9/39) were from embryos with a diameter of 500-850 μm. In conclusion, 1) significantly higher pregnancy rates were achieved when embryos were vitrified using the Fibreplug than using the Cryolock; 2) the effect of BSA on embryo vitrification is dependent on embryo storage device type and embryo diameter; 3) smaller vitrified embryos (<500 μm) tend to produce higher pregnancy rates than larger embryos (≥500 μm), however, the negative effect of embryo size on embryo vitrification is reduced when embryos are frozen using the original novel vitrification kit (no BSA) solid surface vitrification using the CVM.

Comparison of Different Materials for Self-Pressurized Vitrification of Feline Oocytes-First Results

Cryobanking is a crucial part on species conservation. Nowadays, there is no suitable protocol for vitrification of feline oocytes. Self-pressurized rapid freezing of different cell types proved to mimic the advantages of high pressure freezing. As this method could also be applied for gamete rescue under field conditions, the aim here was to analyse the impact of self-pressurized vitrification on feline cumulus-oocyte-complexes (COCs) and to determine the appropriate material. Therefore, COCs of domestic cat were randomly vitrified (n = 189) in metal tubes of different materials: Aluminium, silver, and titanium. No significant differences were found on oocytes' competence after thawing. On average, 44% of the COCs presented normal morphology and 48.2% of them showed a polar body after in vitro maturation (IVM) and were subsequently fertilised. Aluminium tubes were positive on toxicity tests, producing the lowest cleavage rates. Silver tubes showed no toxic effect, but the cleavage rate was lower than with titanium tubes, and a previous association with embryotoxicity and biological alterations makes us aware of its indiscriminate use. Titanium seems to be the only inert material of them, presenting a slightly higher maturation (55.6%) and cleavage (20%) rates. Nevertheless, more studies should follow to increase embryo competence after warming.

ARTIFICIAL OOCYTE ACTIVATION IMPROVES THE LABORATORY AND CLINICAL OUTCOME IN VITRIFIED DONOR OOCYTE GROUP

Introduction: Oocyte donation is proved effective. Vitrification of donor eggs allows creation of donor egg banking. Simultaneously, for good clinical outcome it is recommended to thaw 10-15 oocytes at once. In the current study, we demonstrate the benefit of using artificial oocyte activation in order to reduce the number of thawed donor eggs for IVF program without any affect on laboratory and clinical outcome. Aim of study: To improve the good quality blastocyst formation rate using artificial activation with vitrified donor eggs. Is it possible to increase the clinical pregnancy rate (CPR) and live birth rate (LBR) thawing only 6-8 donor eggs? Materials and Methods: The retrospective cohort studyincluded 40 fresh (Group A) and 12 vitrified (Group B) donor egg programs. ICSI was conducted to all oocytes. In Group B, we also used artificial oocyte activation with calcium ionophore. Student T test was used to infer statistical significance. P value < 0.05 was considered significant. Results: The fertilization and good quality blastocyst formation rate is not different between the groups. The majority of usable blastocysts, 72% in Group A and 93% in Group B were formed on Day 5. The CPR is not statistically different between groups A and B and is 52.5% and 50% respectively. The IR is not statistically significant and is 39% in Group A and 42% in Group B. The LBR is higher in Group A (50%) comparing to Group B (25%), but the difference is not statistically significant. Conclusions: Considering our data, we suggest that artificial oocyte activation is feasible for use with vitrified donor eggs. It might decrease the expenses of patients on thawing less number of donor oocytes without negative impact on the laboratory and clinical outcome.

High-security closed devices are efficient and safe to protect human oocytes from potential risk of viral contamination during vitrification and storage especially in the COVID-19 pandemic

PURPOSE

The main purpose and research question of the study are to compare the efficacy of high-security closed versus open devices for human oocytes' vitrification.

METHODS

A prospective randomized study was conducted. A total of 737 patients attending the Infertility and IVF Unit at S.Orsola University Hospital (Italy) between October 2015 and April 2020 were randomly assigned to two groups. A total of 368 patients were assigned to group 1 (High-Security Vitrification™ - HSV) and 369 to group 2 (Cryotop® open system). Oocyte survival, fertilization, cleavage, pregnancy, implantation, and miscarriage rate were compared between the two groups.

RESULTS

No statistically significant differences were observed on survival rate (70.3% vs. 73.3%), fertilization rate (70.8% vs. 74.9%), cleavage rate (90.6% vs. 90.3%), pregnancy/transfer ratio (32.0% vs. 31.8%), implantation rate (19.7% vs. 19.9%), nor miscarriage rates (22.1% vs. 21.5%) between the two groups. Women's mean age in group 1 (36.18 ± 3.92) and group 2 (35.88 ± 3.88) was not significantly different (P = .297). A total of 4029 oocytes were vitrified (1980 and 2049 in groups 1 and 2 respectively). A total of 2564 were warmed (1469 and 1095 in groups 1 and 2 respectively). A total of 1386 morphologically eligible oocytes were inseminated by intracytoplasmic sperm injection (792 and 594 respectively, P = .304).

CONCLUSIONS

The present study shows that the replacement of the open vitrification system by a closed one has no impact on in vitro and in vivo survival, development, pregnancy and implantation rate. Furthermore, to ensure safety, especially during the current COVID-19 pandemic, the use of the closed device eliminates the potential samples' contamination during vitrification and storage.

Cryopreservation of equine oocytes: looking into the crystal ball

Invitro embryo production has evolved rapidly in the horse over the past decade, but blastocyst rates from vitrified equine oocytes remain quite poor and further research is needed to warrant application. Oocyte vitrification is affected by several technical and biological factors. In the horse, short exposure of immature oocytes to the combination of permeating and non-permeating cryoprotective agents has been associated with the best results so far. High cooling and warming rates are also crucial and can be obtained by using minimal volumes and open cryodevices. Vitrification of invivo-matured oocytes has yielded better results, but is less practical. The presence of the corona radiata seems to partially protect those factors that are necessary for the construction of the normal spindle and for chromosome alignment, but multiple layers of cumulus cells may impair permeation of cryoprotective agents. In addition to the spindle, the oolemma and mitochondria are also particularly sensitive to vitrification damage, which should be minimised in future vitrification procedures. This review presents promising protocols and novel strategies in equine oocyte vitrification, with a focus on blastocyst development and foal production as most reliable outcome parameters.

Oocyte cryopreservation - current scenario and future perspectives: A narrative review

Oocyte cryopreservation is a boon for women undergoing assisted reproductive technology. With the evolution in the technique of cryopreservation over the last three decades, there has been an exponential rise in the number of oocyte cryopreservation cycles for diverse indications. Apart from cancer patients, it has also been promoted as a mode of fertility insurance to overcome the age-related decline in fertility as well as post-surgical decline following endometriosis surgery. The objective of the review is to evaluate its clinical applications, ideal age at freezing, optimal oocyte number, freezing method of choice, efficacy, safety and recent advances. In the last decade, vitrification has surpassed slow freezing for oocyte cryopreservation. Although closed system of vitrification provides the aseptic environment, open vitrification is commonly followed in practice. Early to mid-thirties is a reasonable age group for planned oocyte cryopreservation, although it might be recommended at a younger age, in patients with diminished ovarian reserve. The patients should be motivated to preserve around 14–20 mature oocytes for successful live birth. Various studies have shown comparable fertilisation and pregnancy rates between Intracytoplasmic sperm injection with fresh and frozen-thawed oocytes. The available evidence has shown no increase in the incidence of congenital abnormalities in babies born through vitrified oocytes. In the future, image analysis using artificial intelligence, and spindle visualisation using poloscope may further enhance the outcome of oocyte cryopreservation.

A review of best practices of rapid-cooling vitrification for oocytes and embryos: a committee opinion

The focus of this paper is to review best practices for rapid-cooling cryopreservation of oocytes and embryos. The discussion of best practices includes the types of cryoprotectants and cryo devices typically used. Key performance indicators of rapid-cooling vitrification success are defined.

Equilibrium vitrification of mouse embryos using low concentrations of cryoprotectants

Previously, we developed a method for vitrification of mouse embryos in a near-equilibrium state using EFS35c, PB1 medium containing 35% (v/v) ethylene glycol, and 0.98 M sucrose. This method has advantages in both slow freezing and vitrification. However, since the vitrification solution in this method contains high concentrations of cryoprotectants and thus has high osmolality, the solution would injure oocytes and embryos with high sensitivity to chemical toxicity and high osmolality. In this study, we examined whether embryos could be vitrified in a near-equilibrium state using a solution containing low concentrations of cryoprotectants and thus with low osmolality. To investigate whether embryos were vitrified in a near-equilibrium state, 2-cell mouse embryos were vitrified with EDFS10/10a, PB1 medium containing 10% (v/v) ethylene glycol, 10% (v/v) DMSO, and 0.4 M sucrose, in liquid nitrogen, stored at -80 °C for 4-28 days, and warmed in water at 25 °C. The viability of the embryos was evaluated by the appearance of embryos after warming and developmental ability. When embryos were vitrified in liquid nitrogen using EDFS10/10a, the survival and developmental ability into blastocysts after storage at -80 °C for 7 days were high, indicating that embryos were vitrified in a near-equilibrium state. A high proportion of embryos vitrified with EDFS10/10a developed to term after transportation with dry ice, re-cooling in liquid nitrogen, and transfer to recipients. Therefore, new equilibrium vitrification developed in this study may be useful for oocytes and embryos that are highly sensitive to the toxicity of cryoprotectants and high osmolality.

Fertility preservation during the COVID-19 pandemic: mitigating the viral contamination risk to reproductive cells in cryostorage

Reopening fertility care services across the world in the midst of a pandemic brings with it numerous concerns that need immediate addressing, such as the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the male and female reproductive cells and the plausible risk of cross-contamination and transmission. Due to the novelty of the disease the literature contains few reports confirming an association of SARS-CoV-2 with reproductive tissues, gametes and embryos. Cryobanking, an essential service in fertility preservation, carries the risk of cross-contamination through cryogenic medium and thus calls for risk-mitigation strategies. This review aims to address the available literature on the presence of SARS-CoV-2 on tissues, gametes and embryos, with special reference to the possible sources of cross-contamination through liquid nitrogen. Strategies for risk mitigation have been extrapolated from reports dealing with other viruses to the current global crisis, for safety in fertility treatment services in general, and specifically for oncofertility.

Low cryoprotectant concentration rapid vitrification of mouse oocytes and embryos

Vitrification of mammalian oocytes and embryos is typically a two-step procedure involving two solutions of increasing concentrations of cryoprotectants. In the present study, we report a simple vitrification protocol that uses low cryoprotectant concentration and a single medium (LCSM). This medium, along with the traditional high concentration two media (HCTM) protocol, was used to vitrify mouse oocytes, zygotes, and blastocysts using silica capillary, cryotop, cryolock, and 0.25 ml straws. Survival rates, two-cell rates, and blastocyst formation rates were compared for oocytes and zygotes vitrified using both protocols. Results show that the LCSM protocol was as good as or better than the traditional HCTM protocol for vitrifying mouse MII oocytes and zygotes using silica capillary, cryotop, and cryolock. On the other hand, for blastocysts, only silica capillary using LCSM had comparable results with the traditional HCTM protocol while cryolock and cryotop had significantly lower percentages of re-expanded and hatched blastocysts. Collapsing blastocysts prior to vitrification or longer duration for better cryoprotectant distribution in multicellular embryos may improve the outcome. In conclusion, the LCSM protocol, with one medium of much lower cryoprotectant concentrations and shorter equilibration time, reduces exposure to cryoprotectant toxicity while improves efficiency, consistency and reliability for mammalian oocyte and embryo preservation.

Does duration of cryostorage affect survival rate, pregnancy, and neonatal outcomes? Large-scale single-center study of slush nitrogen (SN2 ) vitrified-warmed blastocysts

OBJECTIVE

To evaluate the effects of the duration of cryostorage on clinical outcomes after embryo transfer of vitrified blastocysts stored in an open-device slush-nitrogen (SN₂ ) system.

METHODS

A retrospective cohort study was carried out on 1632 autologous vitrified-warmed blastocyst transfer cycles between January 2013 and June 2014. Duration of cryostorage was divided into four groups: Group I: 0-6 months (n=937); Group II: 7-12 months (n=299); Group III: 13-24 months (n=165); and Group IV: ≥25 months (n=231). The effects of the duration of cryostorage on the survival rate (SR), clinical pregnancy rate (CPR), live birth rate (LBR), and neonatal outcomes of vitrified blastocysts stored in an open-device SN₂ system were evaluated.

RESULTS

There were no significant differences between groups in SR, CPR, LBR, and neonatal outcomes after autologous vitrified-warmed blastocyst transfer. Multivariate logistic regression analysis showed no effect on LBR from duration of cryostorage.

CONCLUSION

Vitrification using SN₂ and long-term cryostorage in an open-device system are safe and effective and do not significantly affect clinical outcomes after embryo transfer.

Analyses of human granulosa cell vitality by fluorescence activated cell sorting after rapid cooling

In reproductive medicine, the technique of rapid cooling becomes increasingly important for the preservation of tissue and cells. In order to protect the cells, incubation in different cryopreservation solutions is essential. The speed of the cooling process also makes a pivotal contribution to the success of this method. Using Flourescence Activated Cell Sorting (FACS), we investigated the impact of an open rapid and a closed rapid cooling technique on the vitality of human granulosa cells. Furthermore, we examined effects of the different solutions used for rapid cooling and warming before and after rapid cooling. We found a significant lower proportion of vital cells after rapid cooling compared to untreated controls independently of the technique and the tube size. However, we did not find any significant differences between open and closed rapid cooling. In both, a lower proportion of vital granulosa cells were found after incubation in rapid cooling solution only compared to warming solution only. Our results lend support to the conclusion that the difference of cooling-speed between open and closed rapid cooling is, in our settings, not crucial for the success of the procedure and that cryoprotective agents in the rapid cooling solutions have a higher potential to cause severe cell damage than agents used for warming.

Aseptic Cryoprotectant-Free Vitrification of Human Spermatozoa by Direct Dropping into a Cooling Agent

Spermatozoa cryopreservation is used for the management of infertility and some other medical conditions. Routinely applied cryopreservation techniques depend on permeating cryoprotectants and relatively slow freezing rates. Cryoprotectant-free vitrification is an alternative and cost-effective method that is based on rapid cooling of spermatozoa by direct plunging into a cooling agent to prevent lethal intracellular ice crystallization and the detrimental effects of high salt concentrations. One of the problems with this technique is that full sterilization of commercially produced liquid nitrogen, which could be contaminated with different pathogens, is not possible. Here we use a benchtop device for the production of sterile liquid air with the same temperature as liquid nitrogen (-195.7 °C). This has been used to develop aseptic technology for cryoprotectant-free vitrification of human spermatozoa.

Managing and preventing blood-borne viral infection transmission in assisted reproduction: a Canadian Fertility and Andrology Society clinical practice guideline

Fertility care providers have an obligation to provide safe and effective care to patients. When a user of assisted reproductive technology (ART) is living with a blood-borne viral infection (BBVI: HIV, hepatitis C or hepatitis B), physicians and ART laboratory personnel need to know the requirements for providing quality care. Recent developments in the treatment of BBVI and understanding of transmission have changed these requirements. This guideline from the Canadian Fertility and Andrology Society (CFAS) provides comprehensive, evidence-based guidelines for reducing horizontal transmission and cross-contamination in the ART setting.

Cryopreservation of human embryos and oocytes for fertility preservation in cancer and non cancer patients: a mini review

The term 'cryopreservation' illustrates the process of freezing cells and storing at very low temperature in liquid nitrogen (-196 °C). Cooling is not a physiological condition for human cells especially due to the high concentration of water in the living matter, whose conversion to ice crystals may be associated with cell death. Human oocytes are particularly sensitive to the freezing process, primarily because of their large size and the presence of the meiotic spindle, which at low temperature can degenerate. In the last decade, the cryopreservation technology has become highly important as an option for fertility preservation (FP) in women with cancer. Anticancer therapy might promote premature ovarian failure and negatively affects the reproductive outcome. Over the years, scientists have proposed different cryopreservation strategies in the effort to maintain the physiological functions of oocytes and embryo. However, despite the first success obtained in the 1980s with frozen oocytes, it was not until recently that a new approach has been proposed: the 'Vitrification' which allowed a breakthrough in this procedure. FP is a major determinant for cancer survivor women in the reproductive age. This article describes the FP options currently available, focusing mainly on oocyte and embryo cryopreservation.

How does temperature play a role in the storage of extracellular vesicles?

Extracellular vesicles (EVs) contain specific proteins, lipids, and nucleic acids that can be passed to other cells as signal molecules to alter their function. However, there are many problems and challenges in the conversion and clinical application of EVs. Storage and protection of EVs is one of the issues that need further research. To adapt to potential clinical applications, this type of problem must be solved. This review summarizes the storage practices of EVs in recent years, and explains the impact of temperature on the quality and stability of EVs during storage based on current research, and explains the potential mechanisms involved in this effect as much as possible.

Human sperm vitrification: the state of the art

Sperm cryopreservation has been widely used in assisted reproductive technology (ART) and has resulted in millions of live births. Two principal approaches have been adopted: conventional (slow) freezing and vitrification. As a traditional technique, slow freezing has been successfully employed and widely used at ART clinics whereas the latter, a process to solidify liquid into an amorphous or glassy state, may become a faster alternative method of sperm cryopreservation with significant benefits in regard to simple equipment and applicability to fertility centers. Sperm vitrification has its own limitations. Firstly, small volume of load is usually plunged to liquid nitrogen to achieve high cooling rate, which makes large volume sample cryopreservation less feasible. Secondly, direct contact with liquid nitrogen increases the potential risk of contamination. Recently, new carriers have been developed to facilitate improved control over the volume and speed, and new strategies have been implemented to minimize the contamination risk. In summary, although sperm vitrification has not yet been applied in routine sperm cryopreservation, its potential as a standard procedure is growing.

State of the Art in Fertility Preservation for Female Patients Prior to Oncologic Therapies

Quality of life improvement stands as one of the main goals of the medical sciences. Increasing cancer survival rates associated with better early detection and extended therapeutic options led to the specific modeling of patients’ choices, comprising aspects of reproductive life that correlated with the evolution of modern society, and requires better assessment. Of these, fertility preservation and ovarian function conservation for pre-menopause female oncologic patients pose a contemporary challenge due to procreation age advance in evolved societies and to the growing expectations regarding cancer treatment. Progress made in cell and tissue-freezing technologies brought hope and shed new light on the onco-fertility field. Additionally, crossing roads with general fertility and senescence studies proved highly beneficial due to the enlarged scope and better synergies and funding. We here strive to bring attention to this domain of care and to sensitize all medical specialties towards a more cohesive approach and to better communication among caregivers and patients.

Vitrification of in vitro-derived bovine embryos: targeting enhancement of quality by refining technology and standardising procedures

Bovine invitro fertilisation technology has been widely exploited in commercial settings. The majority of invitro-derived cattle embryos are transferred into recipient cows as recently collected (i.e. 'fresh') embryos due to the lack of a reliable cryopreservation method that results in favourable pregnancy rates following transfer of thawed embryos. This is a primary reason for the poor industry uptake of this extreme temperature freezing process. Numerous investigations into vitrification have revealed the importance of rapid cooling and warming rates, enhancing embryo viability after cryopreservation compared with conventional slow freezing. Those studies spawned a considerable assortment of cryovessels and diversity of procedures, delivering variable rates of success, which makes performing vitrification consistently a practical challenge. Hence, further research is required in order to both optimise and standardise vitrification methodology and to design a cryovessel that enables direct transfer of vitrified embryos to recipients after warming. In parallel with improvements in vitrification, it is important to continue to raise the quality of invitro-derived cattle embryos through modifications in laboratory culture techniques. The twin goals of methodology refinement and standardisation, leading to embryo quality enhancement, are each imperative if invitro fertilisation technology is to be adopted in the field.

Slow Freezing Versus Vitrification of Mouse Ovaries: from Ex Vivo Analyses to Successful Pregnancies after Auto-Transplantation

Slow freezing (SF) is the reference method for ovarian tissue cryopreservation. Vitrification (VT) constitutes an alternative but controversial method. This study compares SF and VT (open [VTo] and closed [VTc] systems) in terms of freezing damage and fertility restoration ability. In vitro analyses of C57Bl/6 SF or VTo-ovaries, immediately after thawing/warming or after culture (cult), revealed that event though follicular density was similar between all groups, nuclear density was decreased in VTo-ovaries compared to CT-ovaries (CT = 0.50 ± 0.012, SF = 0.41 ± 0.03 and VTo = 0.29 ± 0.044, p < 0.01). Apoptosis was higher in VTo-cult ovaries compared to SF-cult ovaries (p < 0.001) whereas follicular Bmp15 and Amh gene expression levels were decreased in the ovaries after culture, mostly after VTo (p < 0.001). Natural mating after auto-transplantation of SF, VTo and VTc-ovaries revealed that most mice recovered their oestrous cycle. Fertility was only restored with SF and VTo ovaries (SF: 68%; VTo: 63%; VTc: 0%; p < 0.001). Mice auto-transplanted with SF and VTo-ovaries achieved the highest number of pregnancies. In conclusion, in vitro, no differences between SF and VTo were evident immediately after thawing/warming but VTo ovaries displayed alterations in apoptosis and follicular specific proteins after culture. In vivo, SF and VTo ovary auto-transplantation fully restored fertility whereas with VTc-ovary auto-transplantation no pregnancies were achieved.

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification.

A brief history of oocyte cryopreservation: Arguments and facts

The term "cryopreservation" refers to the process of cooling cells and tissues and storing them at subzero temperatures in order to stop all biological activity and preserve their viability and physiological competences for future use. Cooling to subzero temperatures is not a physiological condition for human cells; this is probably due to the high content of water in the living matter, whose conversion to ice crystals may be associated with severe and irreversible damage. Among reproductive cells and tissues, metaphase II oocytes are notably vulnerable to cryopreservation, mainly because of their large size, low surface area to volume ratio, relatively high water content and presence of the meiotic spindle. As human biological systems lack efficient internal defense mechanisms against chilling injuries, it is of the utmost importance to supply adequate external support, in terms of cryoprotectant additives, appropriate cooling/warming rates, and suitable long-term storage. Over the years, scientists have proposed different cryopreservation strategies in the effort to achieve an optimized recipe ensuring cell survival and, at the same time, maintenance of the physiological functions and abilities necessary to continue life. However, despite the first success obtained in the 1980s with frozen oocytes, it was not until recently that notable improvements in the cryopreservation technique, thanks to the advent of vitrification, allowed a breakthrough of this fine procedure.

Open versus closed vitrification system of human oocytes and embryos: a systematic review and meta-analysis of embryologic and clinical outcomes

BACKGROUND

The objective of this study was to carry out a systematic review and meta-analysis of embryologic and clinical outcomes following open versus closed vitrification of human oocytes and embryos.

METHODS

An electronic literature search was conducted in main electronic databases up to June 30, 2018 using the following key terms: 'oocyte', 'embryo', 'blastocyst', 'vitrification', 'cryopreservation', 'device', 'survival rate', 'pregnancy rate', etc. A meta-analysis was performed using a random effect model to estimate the value of risk ratios (RRs) and 95% confidence interval (CI). Subgroup analyses and sensitivity analyses were carried out to further confirm the results.

RESULTS

Twelve (Eight prospective and four retrospective) studies comparing open versus closed vitrification of human oocytes or embryos were included. For prospective studies on oocytes, no evidence for a significant difference in cryosurvival rate (RR = 0.91, 95% CI: 0.80-1.03, P = 0.14; n = 2048) or clinical pregnancy rate (RR = 1.29, 95% CI: 0.80-2.06, P = 0.30; n = 150) was observed. Additionally, there were no significant differences between the two methods concerning secondary endpoints included positive βHCG rate, implantation rate, miscarriage rate, ongoing pregnancy rate, live birth rate, cancellation rate, babies born per transferred blastocysts, or multiple birth rate (P > 0.05). The results of the retrospective studies were similar as the prospective studies.

CONCLUSIONS

It is still impossible to conclude that closed vitrification system could be a substitution for open system in human oocyte and embryo cryopreservation based on current evidence. Therefore, more well-designed prospective studies addressing these issues are still warranted.

Comparison of pregnancy in cattle when non-vitrified and vitrified in vitro-derived embryos are transferred into recipients

The present study was conducted in cattle to test the null hypothesis that the pregnancy rate of recipient females is similar when in vitro-derived embryos are transferred either fresh (non-vitrified) or after being subjected to vitrification. Cumulus-oocyte complexes, collected twice (6 weeks apart) from 10 donor cows were matured in vitro and inseminated with frozen-thawed sperm from a single proven bull per donor collection. Cleaved embryos were cultured in vitro until day 7 and any resulting blastocysts were graded for stage [early (unexpanded), advanced (expanded, hatching, hatched)] and/or quality and either discarded (poor quality), or, if deemed suitable, transferred fresh or vitrified for later warming and transfer. All blastocysts were transferred singly to oestrus-synchronized cows and pregnancy monitored by transrectal palpation on days 35, 60 and 90. From 20 collections, 818 cumulus-oocyte complexes were aspirated; however, after grading, only 462 (56.5%) were ranked as suitable quality for maturation and insemination. From those 462 complexes inseminated, 363 (78.6%) cleaved during the process and 243 (52.6%) developed to the blastocyst stage with 194 (42.0%) deemed utilizable, of which 85 were vitrified and 109 were transferred fresh. There was a median of 13 (range 0-24) utilizable blastocysts per cow. Of the 109 non-vitrified blastocysts transferred, there were 45 (41.3%) and 41 (37.6%) recipients that were detected to be pregnant on day 35 and day 90, respectively, subsequent to transfer. Thus, an 8.9% abortion rate was observed (4/45). Of the 85 transferred vitrified-warmed blastocysts, 34 were detected to be pregnant (40.0%) on day 35 following transfer, and all pregnancies were maintained at day 90 (0% abortion rate), which was similar to non-vitrified transfers (P > 0.05, Chi-square test). There was no significant difference in pregnancy rate on day 90 in advanced compared to early blastocysts for either the non-vitrified transfers (9/23, 39.1% vs 33/86, 38.3%) or the vitrified transfers (30/72, 41.6% vs 4/13, 30.8%) (P > 0.05 in each case). In summary, these data show that vitrification of in vitro-derived early and advanced blastocysts is a suitable method of cryopreservation of bovine embryos, and, furthermore, that subsequent transfer of all vitrified/warmed blastocysts into recipient females results in pregnancy rates no different to those attained by non-vitrified transfers into recipient females.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.