Survival and post-warming in vitro competence of human oocytes after high security closed system vitrification

Embryology outcomes after oocyte vitrification with super-cooled slush nitrogen are similar to outcomes with conventional liquid nitrogen: a randomized controlled trial

OBJECTIVE

To determine whether the use of slush nitrogen (SN), a super-cooled form of nitrogen with a temperature from -207 to -210 °C, can improve oocyte survival after vitrification and warming compared with conventional liquid nitrogen (LN).

DESIGN

Randomized controlled trial.

SETTING

Academic-affiliated private practice.

PATIENT(S)

A total of 556 metaphase II oocytes from 32 oocyte donor cycles were included.

INTERVENTION(S)

Donor oocytes were block randomized to undergo vitrification with either SN or LN. Vitrification was followed by warming, fertilization with donor sperm, embryo culture to the blastocyst stage, and preimplantation genetic testing for aneuploidy via trophectoderm biopsy with targeted next-generation sequencing.

MAIN OUTCOME MEASURE(S)

The primary outcome was oocyte survival after vitrification and warming. Secondary outcomes included rates of fertilization, usable blastocyst formation, and whole chromosome aneuploidy.

RESULT(S)

Half of the metaphase II oocytes (n = 278) were randomized to undergo vitrification with SN, whereas the other half (n = 278) were randomized to undergo vitrification with LN. There were no statistically significant differences noted in oocyte survival rate (85.3% vs. 86.3%), fertilization rate (84.0% vs. 80.0%), rate of usable blastocyst formation (54.3% vs. 55.7%), or rate of whole chromosome aneuploidy (9.4% vs. 11.7%) between the SN and LN arms, respectively.

CONCLUSION(S)

The implementation of an SN oocyte vitrification protocol resulted in similar embryology outcomes compared with LN. The use of SN did not lead to any demonstrable improvement in oocyte survival after vitrification and warming.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04342364.

The effect of repeated cryopreservation and thawing using cryotip on the clinical outcomes of embryos

PURPOSE

To compare the clinical outcomes of embryo transfers that were cryopreserved and thawed two or three times with those cryopreserved and thawed once by CryoTip.

METHODS

Data for 388 single cryopreserved-thawed blastocyst transfer cycles, performed from April 2012 to March 2014, were assessed. The blastocysts were classified into three groups: blastocysts (A) cryopreserved once, (B) cryopreserved twice, and (C) cryopreserved three times.

RESULTS

The pregnancy rate was 43.8% (134/306) in group A and 46.3% (38/82) in group B, while the miscarriage rate was 29.1% (39/134) in group A and 23.7% (9/38) in group B. The rate of improvement/maintenance of blastocyst grade was 84.0% (257/306) in group A and 80.5% (66/82) in group B. The pregnancy and miscarriage rates of the blastocysts that showed improvement/maintenance in the grade were 45.9% (118/257) and 29.7% (35/118) in group A and 48.5% (32/66) and 21.9% (7/32) in group B, respectively. The pregnancy rate was 33.3% (2/6), while the miscarriage rate was 0.0% (0/2) in group C.

CONCLUSIONS

Pregnancy rates achieved with re-cryopreserved and rethawed blastocyst transfer were comparable to those achieved with single cryopreserved-thawed blastocyst transfer.

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.

'Two countries-two labs': the transnational gamete donation (TGD) programme to support egg donation

PURPOSE

To evaluate the effectiveness, efficiency, and safety of a transnational gamete donation (TGD) programme based on the shipping of vitrified donor oocytes.

METHODS

A retro-prospective observational study was conducted in the Assisted Reproductive Technology Center of the University Hospital of Florence, Italy. The study population included 622 consecutive donor oocyte cycles. A mean number of 6 vitrified oocytes per couple were shipped from two Spanish biobanks. In the receiving centre, gametes were warmed and inseminated and the subsequent embryo transfer (ET) was performed. The main outcome measurement was LBR. Secondary outcomes included oocyte survival rate, ICSI damage rate, normal fertilization, cleavage, and implantation rate (IR) in both 'fresh' and cryotransfer cycles.

RESULTS

A total number of 3536 mature oocytes were warmed with 81.4% surviving oocytes. 2PN oocytes were 1941 with an ICSI normal fertilization rate of 70.4% and a cleavage rate of 93.4%; 857 day-3 embryos were transferred in 498 women, 63 blastocysts in 44. Couples with at least one vitrified embryo were 181 (32.3%). IR was 25.1% and 33.1% for day-3 ET and blastocyst stage respectively. Crude pregnancy rate and LBR after the first ET were 35.5% and 27% correspondingly with a conservative cumulative LBR of 34% and an optimal LBR of 51.4%.

CONCLUSION

Imported vitrified donor oocytes retain their competence and are capable of resulting in ongoing pregnancies and healthy babies in a proportion comparable to other existing systems as egg donation with vitrification/warming in the same laboratory and transnational fresh oocyte donation.

Cryopreservation of Mammalian Oocytes: Slow Cooling and Vitrification as Successful Methods for Cryogenic Storage

Two basic methods for the laboratory-focused cryopreservation of mammalian oocytes are described, based on work with murine oocytes. One method uses a relatively low concentration of the cryoprotectant propanediol plus sucrose and requires controlled rate cooling equipment to achieve a slow cooling rate. This method has also produced live births from cryopreserved human oocytes. The second method, which is described here, employs a high concentration of the cryoprotectant dimethyl sulfoxide plus a low concentration of polyethylene glycol. This is a vitrification method, which involves ultra-rapid cooling by plunging standard straws into liquid nitrogen vapor, hence avoiding the need for specialized equipment, but requires technical ability to manipulate the oocytes quickly in the highly concentrated cryoprotectant solutions. Murine oocytes that have been vitrified using this technique have resulted in live births. Vitrification using other cryoprotectant mixtures is now a popular clinically accepted method for cryobanking of human oocytes.

Closed vitrification system and egg donation: Predictive factors of oocyte survival and pregnancy

Although many studies have demonstrated the superiority of ultra-fast freezing compared with slow freezing, the debate is still ongoing concerning the best type of vitrification method: direct exposure to liquid nitrogen (i.e., open systems), or sterile system without contact with liquid nitrogen (i.e., closed systems). The aims of this study were to share our experience on closed vitrification systems in the framework of our egg donation programme with fully asynchronous cycles, and to identify predictive factors of successful outcome in this context. Logistic regression analysis indicated that the number of vitrified oocytes was the only factor predictive of the oocyte survival rate and of clinical pregnancy. The addition of one vitrified oocyte increased by 15 % the odds of oocyte survival. When the oocyte survival rate was considered as a continuous variable, the following results were obtained: 7 % of clinical pregnancy probability for 50 % survival rate, 15 % for 75 % survival rate, and 32 % for 100 % survival rate. The rates of oocyte survival and fertilization, embryo implantation, and clinical pregnancy were in agreement with the recommended values established by ALPHA Scientists in Reproductive Medicine in 2012. On the basis of these results, and according to the European directives on safety, we validate the routine use of closed oocyte vitrification systems for egg donation programmes. These results must be confirmed in larger samples before extrapolation to all patient types.

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 new vitrification device that absorbs excess vitrification solution adaptable to a closed system for the cryopreservation of mouse embryos

Several closed vitrification devices that avoid contact with liquid nitrogen have been reported. Recently, based on the Kitasato Vitrification System (KVS), we developed the Closed-KVS, which is a closed vitrification device. The KVS is an open vitrification device that can absorb excess vitrification solution. In this study, we performed two experiments to evaluate the efficacy of the Closed-KVS as a vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage. In the first experiment, the blastocysts were vitrified using either the Closed-KVS or the KVS (control device). The survival, re-expansion, and hatching rates were not significantly different between embryos vitrified using the Closed-KVS and those vitrified using the KVS. In the second experiment, we evaluated the embryonic development of the two-cell stage embryos vitrified using the Closed-KVS. There were no significant differences in the survival, blastocyst formation, or hatching rates between vitrified or non-vitrified embryos. Additionally, we evaluated the cooling and warming rates of these devices using a numerical simulation method. The cooling rates of the Closed-KVS were similar regardless of whether the outer cap was pre-cooled and were lower than those of the KVS. However, the warming rates of the Closed-KVS (irrespective of cap pre-cooling) were the same as those of the KVS (612,000 °C/min). In summary, the Closed-KVS is a novel closed vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage.

Comparison of two closed carriers for vitrification of human blastocysts in a donor program

The survival of human blastocysts to vitrification with two different carriers is compared. Both vitrification carriers used in this study are in the category of closed carriers, as they completely isolate the samples from direct contact with liquid nitrogen or its vapours during cooling and storage, until warming. This characteristic is appealing because it reduces or eliminates the theoretical risk of cross-contamination during that period of time. The two closed vitrification systems used present very different design and features: in the High Security Vitrification device, the carrier straw containing the embryos is encapsulated inside an external straw before plunging in liquid nitrogen, resulting in thermal insulation during cooling. On the other hand, in the SafeSpeed carrier embryos are loaded in a thin-walled, narrow capillary designed to maximize the thermal transference. Both closed carriers achieved comparable outcomes in terms of survival of blastocysts to the vitrification process, with 97.5% vs. 96.1% survival with HSV and SafeSpeed, respectively. In conclusion, the cooling and warming rates at which these carriers operate, in combination with the cytosolic solute concentration in the cells of the cryopreserved blastocysts attained after a cryoprotectant-loading protocol, result in successful vitrification of human blastocysts for human assisted reproduction.

Risk of Contamination of Gametes and Embryos during Cryopreservation and Measures to Prevent Cross-Contamination

The introduction and widespread application of vitrification are one of the most important achievements in human assisted reproduction techniques (ART) of the past decade despite controversy and unclarified issues, mostly related to concerns about disease transmission. Guidance documents published by US Food and Drug Administration, which focused on the safety of tissue/organ donations during Zika virus spread in 2016, as well as some reports of virus, bacteria, and fungi survival to cryogenic temperatures, highlighted the need for a review of the way how potentially infectious material is handled and stored in ART-related procedures. It was experimentally demonstrated that cross-contamination between liquid nitrogen (LN₂) and embryos may occur when infectious agents are present in LN₂ and oocytes/embryos are not protected by a hermetically sealed device. Thus, this review summarizes pertinent data and opinions regarding the potential hazard of infectious transmission through cryopreserved and banked reproductive cells and tissues in LN₂. Special attention is given to the survival of pathogens in LN₂, the risk of cross-contamination, vitrification methods, sterility of LN₂, and the risks associated with the use of straws, cryovials, and storage dewars.

Analysis of embryo intactness and developmental potential following slow freezing and vitrification

The aim of this study was to identify the parameters that are related to intactness and developmental potential of a day 3 embryo after warming to improve the selection criteria used to cryopreserve and transfer embryos. We also sought to compare slow freezing and vitrification methods of cryopreservation and to evaluate the viability of non-intact embryos. Embryos warmed following slow freezing (n=220) or vitrification (n=522) were divided into 3 groups according to the proportion of surviving blastomeres (I<50%; II=50-99%; and III=100%). The developmental potential of embryos, including the mitosis resumption rate, blastocyst formation rate, and formation rate of grade A blastocysts (i.e., fully expanded blastocysts with an inner cell mass and grade A or B trophectoderm) were retrospectively assessed in embryos. Cleavage-stage embryos with <50% blastomere survival were analyzed using next-generation sequencing (NGS). Logistic regression analysis showed that vitrification and grade 1 were independent predictive factors of embryo intactness and developmental potential (all p<0.05). On day 3, embryos with 4-6 cells or blastomere damage had lower developmental potential than those with 7-9 cells or intact blastomeres (all p<0.05). NGS results showed that the chromosomal status was completely normal in 8 embryos that developed into expanded blastocysts, whereas 4 out of 5 embryos in which development was arrested were abnormal. The results of this study suggest that vitrification is a better choice than slow freezing for embryo cryopreservation. Embryos showing poor quality (fragmentation >30% and/or a non-stage-specific cell size) and lower cell numbers (4-6 cells) on day 3 should be cultured to the blastocyst stage and then vitrified if they develop into good-quality blastocysts. The developmental potential of non-intact embryos is lower than that of intact embryos; however, after they are cultured to the fully expanded blastocyst stage, embryos with <50% blastomere survival appear to be better candidates for transfer. Abbreviations ART: assisted reproductive technology; grade A blastocyst: fully expanded blastocyst with an inner cell mass and grade A or B trophectoderm; NGS: next-generation sequencing; IVF: in vitro fertilization; ICSI: intracytoplasmic sperm injection; FET: frozen-thawed embryo transfer.

Safety and efficiency of oocyte vitrification

As the oocyte is the starting point for a new life, artificial reproductive technology (ART) techniques should not affect the (ultra) structural and functional integrity, or the developmental competence. Oocyte vitrification -one of the most significant achievements in human ART during the past decade- should therefore be a safe and efficient technique. This review discusses the principles and developments of the existing and future techniques, applications possibilities and safety concerns. The broad range of vitrification media and devices that are currently available, show differences in their effects on the oocyte ultrastructure and preimplantation development. It is not yet fully decided whether this has an influence on the obstetric and neonatal outcome, since only limited information is available with different media and devices. For autologous oocytes, the obstetric and neonatal outcomes appear promising and comparable to pregnancies obtained with fresh oocytes. This however, is not the case for heterologous fresh or vitrified oocytes, where the immunological foreign foetus induces adverse obstetric and neonatal outcomes. Besides the oocyte vitrification process itself, the effect of multiple stimulations (for oocyte banking or for oocyte donors), seems to influence the possibility to develop gynaecological cancers further in life. Automated vitrification/warming should offer a consistent, cross-contamination free process that offers the highest safety level for the users. They should also produce more consistent results in survival, development and clinical pregnancies between different IVF clinics.

Thermal and clinical performance of a closed device designed for human oocyte vitrification based on the optimization of the warming rate

Although it was qualitatively pointed out by Fahy et al. (1984), the key role of the warming rates in non-equillibrium vitrification has only recently been quantitatively established for murine oocytes by Mazur and Seki (2011). In this work we study the performance of a closed vitrification device designed under the new paradigm, for the vitrification of human oocytes. The vitrification carrier consists of a main straw in which a specifically designed capillary is mounted and where the oocytes are loaded by aspiration. It can be hermetically sealed before immersion in liquid nitrogen for vitrification, and it is warmed in a sterile water bath at 37 °C. Measured warming rates achieved with this design were of 600.000 ºC/min for a standard DMEM solution and 200.000 ºC/min with the vitrification solution for human oocytes. A cohort of 143 donor MII sibling human oocytes was split into two groups: control (fresh) and vitrified with SafeSpeed device. Similar results were found in both groups: survival (97.1%), fertilization after ICSI (74.7% in control vs. 77.3% in vitrified) and good quality embryos at day three (54.3% in control vs. 58.1% in vitrified) were settled as performance indicators. The pregnancy rate was 3/6 (50%) for the control, 2/3 (66%) for vitrified and 4/5 (80%) for mixed transfers.

Closed vitrification of human oocytes and blastocysts: outcomes from a series of clinical cases

PURPOSE

High survival rates and clinical outcomes similar to those from fresh oocytes and blastocysts have been observed with open oocyte vitrification systems. It has been suggested that the extremely fast cooling rates that are only achieved with open systems are necessary for human oocyte and blastocyst vitrification. However, there is a potential risk of introducing contamination with open systems. The aim of this study was to assess whether similar survival and subsequent implantation rates could be achieved using a closed vitrification system for human oocytes and blastocysts.

METHODS

Initially, donated immature oocytes that were matured in vitro were vitrified using the cryoprotectants ethylene glycol (EG) + dimethyl sulphoxide (DMSO) + sucrose and either a closed system (Rapid-i®) or an open system (Cryolock). The closed system was subsequently introduced clinically for mature oocyte cryopreservation cases and blastocyst vitrification.

RESULTS

Using in vitro matured oocytes, a similar survival was achieved with the open system of 92.4 % (73/79) and with the closed system of 89.7 % (35/39). For clinical oocyte closed vitrification, high survival rate of 90.5 % (374/413) and an implantation rate of 32.7 % (18/55) from the transfer of day 2 embryos was achieved, which is similar to fresh day 2 embryo transfers. Blastocysts have also been successfully cryopreserved using the Rapid-i closed vitrification system with 94 % of blastocysts having an estimated ≥75 % of cells intact and a similar implantation rate (31.5 %) to fresh single blastocyst transfers.

CONCLUSION

Closed vitrification can achieve high survival and similar implantation rates to fresh for both oocytes and blastocysts.

[A prospective study to compare the efficiency of oocyte vitrification using closed or open devices]

OBJECTIVES

Oocyte vitrification using an open device is thought to be a source of microbiological and chemical contaminations that can be avoided using a closed device. The principal purpose of this study was to compare the two vitrification protocols: closed and open system. The secondary aim was to study the effects of the storage in the vapor phase of nitrogen (VPN) on oocytes vitrified using an open system and to compare it to those of a storage in liquid nitrogen (LN).

METHODS

Forty-four patients have been included in our study between November 2014 and May 2015. Two hundred and fourteen oocytes have been vitrified at germinal vesicle (GV), metaphase I (0PB) and metaphase II (1PB) stages. We vitrified 96 oocytes (59 GV/37 0PB) using a closed vitrification device and 118 oocytes (57 GV/31 0PB/30 1PB) using an open device. The vitrified oocytes were then stored either in LN or in VPN. The main outcome measures were the survival rate after warming (SR), meiosis resumption rate (MRR) and maturation rate (MR).

RESULTS

The global post-thaw SR was significantly higher for oocytes vitrified using an open system (93.2%) compared to those vitrified using a closed one (64.5%; P<0.001). On the contrary, there was no significant difference in terms of global MRR and MR (82.1% vs. 87.5% and 60.7% vs. 61.2% using closed and open system respectively). The SR, MRR and the MR were not significantly different when vitrified oocytes were stored in VPN or LN (91.6, 83.8, 64.5% vs. 93.9, 89.8, 59.1% respectively).

CONCLUSION

Taking into account the limits of our protocol, the open vitrification system remains the more efficient system. The use of sterile liquid nitrogen for oocyte vitrification and the subsequent storage in vapor phase of nitrogen could minimize the hypothetical risks of biological and chemical contaminations.

Open versus closed oocyte vitrification in an oocyte donation programme: a prospective randomized sibling oocyte study

STUDY QUESTION

Is the survival of donor oocytes with the CryotopSC device superior to the survival with the closed CBSvit device?

SUMMARY ANSWER

The CryotopSC device and the CBSvit device showed similar survival rates.

WHAT IS KNOWN ALREADY

Health authorities are cautious about possible cross contamination during liquid nitrogen storage or handling when working with open vitrification devices. At present, the use of open devices is still allowed since little information is available on the efficiency of closed devices.

STUDY DESIGN, SIZE, DURATION

A prospective randomized sibling oocyte study was performed in the Centre for Reproductive Medicine (UZBrussel) between January 2014 and July 2015. The survival after warming and the embryological outcome of donor oocytes vitrified using two devices was compared: the CBSvit device (closed vitrification and closed storage) and the CryotopSC device (open vitrification and closed storage). A difference of 10% was defined to prove the superiority of the CryotopSC device. In total, 250 warmed oocytes were needed in each arm.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oocytes from 48 donors were included in the study: 253 vitrified with the CBSvit device and 257 with the CryotopSC device. Equal numbers of oocytes from both devices and originated from the same donor cycle were allocated to each of 78 recipients, in order to exclude donor and recipient (male factor) effects.

MAIN RESULTS AND THE ROLE OF CHANCE

There were no differences found between the CBSvit and the CryotopSC in terms of survival after warming (93.7 versus 89.9%) or fertilization per injected oocyte (74.3 versus 81.4%). The degeneration rate after ICSI was significantly higher for the CBSvit device: 11.4 versus 6.1% (P = 0.041). A significantly higher number of zygotes in the CryotopSC group finished their first mitosis 25-27 h post-injection (34.1 versus 52.1%, P = 0.001). On Day 3, the overall embryo quality distribution did not vary between groups, but a significantly higher cell number was obtained in the CryotopSC device: 6.8 ± 2.8 versus 7.6 ± 2.8 (P = 0.01). The utilization rate per mature oocyte, per surviving oocyte or per fertilized oocyte did not differ. The embryos with the highest quality were selected for transfer on Day 3. The clinical pregnancy rate per transfer cycle was 36.5%.

LIMITATIONS, REASONS FOR CAUTION

The results of this study should not be extrapolated to other female groups, since oocytes from young fertile donors were used in this study.

WIDER IMPLICATIONS OF THE FINDINGS

In many countries, the use of open devices is still allowed due to the limited reports on the efficiency of closed devices. Knowing the caution of health authorities about the use of open devices, there is an urgent need for efficiency studies with closed devices. The results obtained in the current study shows the efficiency of a safe closed vitrification device, leaving behind any concern about possible cross contamination during handling or storage.

STUDY FUNDING/COMPETING INTERESTS

No funding was obtained. The authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

NCT01952184.

TRIAL REGISTRATION DATE

24 September 2013.

DATE OF FIRST PATIENT'S ENROLMENT

23 January 2014.

Neonatal outcomes after the implantation of human embryos vitrified using a closed-system device

PURPOSE

Closed vitrification poses a risk of adversely affecting embryo development, while it may minimize the risk of contamination. We assessed the effects of closed-system human embryo vitrification on fetal development after implantation, neonatal outcome, and clinical safety.

METHODS

This was a retrospective cohort study conducted at a private fertility clinic. A total of 875 vitrified-warmed blastocysts that were single-transferred under hormone-replacement cycles between November 2011 and December 2013 were randomly divided into two groups (closed vitrification, n 313; open vitrification, n 562) after receiving the patients' consent forms. Developmental competence after implantation, including gestational age, birth weight, sex, Apgar score, and anomalies of newborns, after the transfer of blastocysts vitrified by closing vitrification was compared with that obtained in the case of open vitrification.

RESULTS

There were no significant differences between the use of closed and open vitrification systems in embryo development after implantation, gestational age, birth weight, sex ratio, Apgar score, and congenital anomalies of newborns.

CONCLUSION

Human embryos can be vitrified using a closed vitrification system without impairment of neonatal development.

A closed system supports the developmental competence of human embryos after vitrification : Closed vitrification of human embryos

PURPOSE

Closed-system vitrification may enable the risk of contamination to be minimised. We performed three studies to compare the developmental competence of human embryos vitrified using either a closed vitrification system (CVS; Rapid-i®) or an open vitrification system (OVS; Cryo-top®).

METHODS

The first study was performed in vitro using 66 zygotes previously vitrified at pronuclear stage. These were warmed and randomised 1:1 to revitrification using either the OVS or the CVS. After re-warming, embryo development and blastocyst cell number were assessed. For the second study, also performed in vitro, 60 vitrified-warmed blastocysts were randomised 1:1:1 into three groups (OVS or CVS revitrification, or no revitrification). The proportion of dead cells was assessed by staining. The third study was performed in vivo, using 263 high-grade blastocysts randomly assigned to vitrification using either the CVS (n = 100) or the OVS (n = 163). After warming, single blastocyst transfer was performed.

RESULTS

There were no differences between the CVS and the OVS in survival rate (100 % vs. 97 %), blastulation rate (96 h: 50 % vs. 50 %; 120 h: 68 % vs. 56 %), proportion of good blastocysts (96 h: 32 % vs. 22 %, 120 h: 47 % vs. 41 %), or mean number of cells (137 vs. 138). The proportion of dead cells in blastocysts re-vitrified by CVS (31 %) was similar to that for OVS (38 %) and non-revitrification (32 %). In vivo, the implantation rate for blastocysts vitrified using the CVS (54 %) was similar to that with the OVS (53 %).

CONCLUSION

Our studies consistently indicate that human embryos may be vitrified using a CVS without impairment of developmental competence.