Effect of varying equilibration time in a two-step vitrification method on the post-warming DNA integrity of mouse blastocysts

Accumulation of Cleavage-Stage Embryos by Vitrification may Compromise Embryonic Developmental Potential in Preimplantation Genetic Testing

It was suggested that the embryo pooling was an alternative for patients with insufficient number of embryos for preimplantation genetic testing (PGT) in a single ovarian stimulation cycle. However, limited study noticed whether it is an efficient strategy to pool cleavage-stage embryos by vitrification. This study included 71 cycles with vitrified-warmed and fresh embryos simultaneously for PGT between May 2016 and May 2021. The embryos from the same patients were split into two groups based on the origin: warming group and fresh group. Embryo development, sequencing results, clinical and neonatal outcomes were compared. The results showed that the rate of high-quality embryos in the warming group was significantly higher than that in the fresh group (64.53% versus 52.61%, P = 0.011); however, the available blastocyst rate in this group was significantly lower than that in the fresh group (47.29% versus 57.83%, P = 0.026). There were 96 and 144 blastocysts that underwent trophectoderm (TE) biopsy in warming and fresh groups, respectively. The high-quality blastocyst rate was significantly lower in the warming group compared to the fresh group (57.29% versus 70.14%, P = 0.041). The rates of genetic transferable blastocyst were comparable between the two groups (P = 0.956). There were no statistical differences in terms of embryo implantation, clinical pregnancy, miscarriage rates, and neonatal outcomes between the two groups. In conclusion, this study demonstrated that the cleavage-stage embryo pooling strategy might be unfavorable for the maintenance of embryonic development potential. If not necessary, it is not recommended to pool cleavage-stage embryos for PGT.

Development of Optimized Vitrification Procedures Using Closed Carrier System to Improve the Survival and Developmental Competence of Vitrified Mouse Oocytes

The open carrier system (OC) is used for vitrification due to its high efficiency in preserving female fertility, but concerns remain that it bears possible risks of cross-contamination. Closed carrier systems (CC) could be an alternative to the OC to increase safety. However, the viability and developmental competence of vitrified/warmed (VW) oocytes using the CC were significantly lower than with OC. We aimed to improve the efficiency of the CC. Metaphase II oocytes were collected from mice after superovulation and subjected to in vitro fertilization after vitrification/warming. Increasing the cooling/warming rate and exposure time to cryoprotectants as key parameters for the CC effectively improved the survival rate and developmental competence of VW oocytes. When all the conditions that improved the outcomes were applied to the conventional CC, hereafter named the modified vitrification/warming procedure using CC (mVW-CC), the viability and developmental competence of VW oocytes were significantly improved as compared to those of VW oocytes in the CC. Furthermore, mVW-CC increased the spindle normality of VW oocytes, as well as the cell number of blastocysts developed from VW oocytes. Collectively, our mVW-CC optimized for mouse oocytes can be utilized for humans without concerns regarding possible cross-contamination during vitrification in the future.

A Shorter Equilibration Period Improves Post-Warming Outcomes after Vitrification and in Straw Dilution of In Vitro-Produced Bovine Embryos

This study was designed to the optimize vitrification and in-straw warming protocol of in vitro-produced bovine embryos by comparing two different equilibration periods, short equilibrium (SE: 3 min) and long equilibrium (LE: 12 min). Outcomes recorded in vitrified day seven (D7) and day eight (D8) expanded blastocysts were survival and hatching rates, cell counts, apoptosis rate, and gene expression. While survival rates at 3 and 24 h post-warming were reduced (p < 0.05) after vitrification, the hatching rates of D7 embryos vitrified after SE were similar to the rates recorded in fresh non-vitrified blastocysts. The hatching rates of vitrified D8 blastocysts were lower (p < 0.05) than of fresh controls regardless of treatment. Total cell count, and inner cell mass and trophectoderm cell counts were similar in hatched D7 blastocysts vitrified after SE and fresh blastocysts, while vitrified D8 blastocysts yielded lower values regardless of treatment. The apoptosis rate was significantly higher in both treatment groups compared to fresh controls, although rates were lower for SE than LE. No differences emerged in BAX, AQP3, CX43, and IFNτ gene expression between the treatments, whereas a significantly greater abundance of BCL2L1 and SOD1 transcripts was observed in blastocysts vitrified after SE. A shorter equilibration vitrification protocol was found to improve post-warming outcomes and time efficiency after in-straw warming/dilution.

Effect of equilibration time on clinical and neonatal outcomes in human blastocysts vitrification

PURPOSE

Prolonged exposure to equilibration solutions may be detrimental to an embryo's developmental potential, whereas a shorter exposure may affect the penetration of cryoprotectants into blastomeres. The purpose of this study was to evaluate the effects of different equilibration times on the clinical and neonatal outcomes of human blastocyst vitrification.

METHODS

This is a retrospective study based on data collected between November 2008 and November 2015. A total of 192 blastocysts (80 non-expanded and 112 expanded) obtained from 167 patients were analyzed. The blastocysts were divided into two groups according to their equilibration time: 8-11 minutes or 12-15 minutes. The clinical and neonatal outcomes of warmed blastocysts were evaluated.

RESULTS

The survival, implantation, and live birth rates of non-expanded blastocysts were not different between the two groups, but they significantly improved for the expanded blastocysts in the 12-15 minutes group compared to the 8-11 minutes group. The results were similar for the neonatal outcomes after vitrified embryo transfer, when partitioned by equilibration time and blastocyst stage at vitrification.

CONCLUSIONS

For the non-expanded blastocysts, a shortened equilibration time (8-11 minutes) is sufficient for effective vitrification.

Optimal timing of blastocyst vitrification after trophectoderm biopsy for preimplantation genetic screening

Is the timing of vitrification after trophectoderm (TE) biopsy associated with successful implantation and pregnancy after the embryo transfer of blastocysts subjected to preimplantation genetic screening (PGS)? In this retrospective cohort study, 1329 blastocysts from 223 patients were subjected to TE biopsy for performing array comparative genomic hybridization (CGH) tests. The PGS and frozen blastocyst transfer (FET) cycles were performed from December 2012 to May 2015. Only the good quality and expanded blastocysts on day 5 or 6 were selected for biopsy. After TE biopsy, the re-expansion grades relative to the original blastocoel were (1) collapsed blastocysts (CB), (2) 3/4 re-expansion but not full expansion (RE), and (3) full re-expansion or hatching (FE). All biopsied blastocysts were subjected to vitrification within 0.5-6 h after biopsy; the time intervals between TE biopsy and vitrification and the expansion grades at the time of vitrification were recorded. By combining two factors, namely the expansion grades and culture intervals between biopsy and vitrification, the patients were further divided into four groups, namely CB with a < 3 h culture interval (n = 34 cycles, Group I), RE and FE blastocysts with a < 3 h culture interval (n = 10 cycles, Group II); CB blastocysts with a ≥ 3 h culture interval (n = 6 cycles, Group III); and RE or FE blastocysts with a ≥ 3 h culture interval (n = 173 cycles, Group IV). The implantation (63.7%, 179/281) and clinical pregnancy (74.0%, 128/173) rates in Group IV were significantly higher than those in Group I (45.3%, 24/53; 50.0%, 17/34; P = 0.012 and 0.005, respectively). According to our findings, optimal vitrification timing > 3 hours to enable blastocysts to reach RE or FE provides improved implantation and pregnancy rates after FET.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03065114.

Which Stage of Mouse Embryos Is More Appropriate for Vitrification?

Background

Vitrification has been shown as one of the most effective methods of cryopreservation for mammalian embryos. However, there is no consensus which stage of embryonic development is the most appropriate for vitrification with subsequent maximal development after thawing. This study was carried out to explore and compare the effect(s) of vitrification on mouse 2-cell, 4-cell, 8-cell, morula and blastocyst stage embryos and subsequent blast formation and hatching after thawing.

Materials and Methods

In this experimental study, 2-cell embryos were obtained from the oviducts of super ovulated female NMRI mice. Some embryos were randomly selected and vitrified through a two-step media protocol and cryotop. Other embryos were cultured to assess their development. During the ensuing days, some of these cultured embryos were vitrified at 4-cell, 8-cell, morula and blastocyst stages. After 10 to 14 days, the embryos were thawed to assess their survival and also cultured to determine the rate of blastocyst formation and hatching. The results were analyzed using one-way ANOVA and Tukey’s post-hoc tests.

Results

There was no significant difference in the survival rates of vitrified embryos at 2-cell, 4-cell, 8-cell, morula and blastocyst stages after thawing (P>0.05). The blastocyst formation rate of vitrified 8-cell embryos was significantly higher than that of 2-cell embryos (P<0.05). The hatching rate of vitrified 4-cell, 8-cell and blastocysts were significantly higher than that of 2-cell embryos (P<0.05).

Conclusion

Vitrification is suitable for cryopreservation of all stages of mouse embryonic development. However, the best tolerance for vitrification was observed at 4and 8-cell stages of development. Accordingly, the development of vitrified embryos to blastocysts, following thawing, was most efficacious for 4 and 8-cell embryos. Compared to mouse 2-cell embryos, embryos vitrified as blastocysts had the highest rate of hatching.

Shortened equilibration time can compromise clinical outcomes in human embryo vitrification

Vitrification is an important way to cryopreserve human embryos and the recommended time of embryo exposure to the vitrification solution is 1 min. However, practically speaking, the duration of embryos exposure to equilibration solution can vary from 5 to 15 min. The purpose of this study was to investigate the effect of different equilibration times on the outcomes of frozen-thawed embryo transfer cycles. The data were collected from our medical records from January 2012 to June 2013 and a total of 517 cycles were included. These cycles were divided into four groups according to the equilibration time: (i) 5-6 min; (ii) 7-8 min; (iii) 9-10 min and (iv) 11-12 min. The results show that there were no differences in terms of survival rate and fully intact embryo rate among the four groups. However, lower clinical pregnancy, embryo implantation and live birth rates were observed in the 5-6 min exposure group (54.6%, 31.9% and 48.2%, respectively) compared with the three other groups. The corresponding rates in the 9-10 min group (73.5%, 47.6% and 64.7%) were the highest. This study indicated that different equilibration times influenced the clinical outcomes of human embryo vitrification and vitrification with shortened equilibration time compromised the clinical outcomes. Appropriate prolongation of the equilibrium time would probably improve the clinical outcomes.

Efficiency of an automatic dehydrated carrier for the vitrification of human embryos derived from three pronuclei fertilized zygotes

The efficiency of a new vitrification technique using embryos obtained after abnormal fertilization was assesed. A total of 100 embryos were vitrified, 48 with the automatic dehydrated carrier (ADC) technique and 52 with cryotop. The survival rates in ADC and cryotop groups were similar (85.4% versus 92.3%). The loss rates of 10.4% for the ADC group and 1.9% for the cryotop group were not significantly different. The intact rate was significantly lower in the ADC group (26.8% versus 64.6%; P = 0.001). After 48 h of culture, blastocyst formation rates in the ADC and cryotop groups were 14.6% and 25.0%, respectively, which were not significantly different. In conclusion, the practicability of ADC vitrification was demonstrated. The study has some limitations, which necessitates further work.

Vitrification of mouse embryos using the thin plastic strip method

OBJECTIVE

The aim of this study was to compare vitrification optimization of mouse embryos using electron microscopy (EM) grid, cryotop, and thin plastic strip (TPS) containers by evaluating developmental competence and apoptosis rates.

METHODS

Mouse embryos were obtained from superovulated mice. Mouse cleavage-stage, expanded, hatching-stage, and hatched-stage embryos were cryopreserved in EM grid, cryotop, and TPS containers by vitrification in 15% ethylene glycol, 15% dimethylsulfoxide, 10 µg/mL Ficoll, and 0.65 M sucrose, and 20% serum substitute supplement (SSS) with basal medium, respectively. For the three groups in which the embryos were thawed in the EM grid, cryotop, and TPS containers, the thawing solution consisted of 0.25 M sucrose, 0.125 M sucrose, and 20% SSS with basal medium, respectively. Rates of survival, re-expansion, reaching the hatched stage, and apoptosis after thawing were compared among the three groups.

RESULTS

Developmental competence after thawing of vitrified expanded and hatching-stage blastocysts using cryotop and TPS methods were significantly higher than survival using the EM grid (p<0.05). Also, apoptosis positive nuclei rates after thawing of vitrified expanded blastocysts using cryotop and TPS were significantly lower than when using the EM grid (p<0.05).

CONCLUSION

The TPS vitrification method has the advantages of achieving a high developmental ability and effective preservation.

Cytoskeletal analysis of human blastocysts by confocal laser scanning microscopy following vitrification

BACKGROUND

Vitrification of human blastocysts is being used increasingly to cryopreserve supernumerary embryos following IVF. In this study, we investigate the effects of aseptic vitrification on the cytoskeleton and development of human blastocysts, by analysing survival rates and spindle and chromosome configurations by fluorescence and confocal laser scanning microscopy.

METHODS

A total of 55 fresh blastocysts and 55 day 5 dimethylsulphoxide/ethylene glycol vitrified blastocysts, which were allowed to remain in culture for 24 h post-warming, were rapidly fixed in ice cold methanol, and immunostained with an a-tubulin antibody to visualize microtubules in combination with antibodies against acetylated tubulin (to visualize spindles, poles and mid bodies), gamma tubulin (to identify spindle poles) and 4(6-diamidino-2-phenylindole) to visualize DNA.

RESULTS

In total, 213 spindles were analysed in the control (fresh) group of which 183/213 (85.9%) were normal, 20/213 (9.4%) were abnormally shaped, 9/213 (4.2%) were multipolar and 1/213 (0.5%) was monopolar. A total of 175 spindles were analysed in the vitrified group, of which 120/175 (68.6%) were normal, 39/175 (22.3%) were abnormally shaped, 10/175 (5.7%) were multipolar and 6/175 (3.4%) were monopolar. The incidence of multipolar spindles was similar in the two groups, but the level of abnormally shaped spindles, often associated with chromosome lagging, or congression failure, was significantly higher in the vitrified group compared with the fresh group (P< 0.05).

CONCLUSIONS

The high survival rate following thawing and the large proportion of normal spindle/chromosome configurations suggests that vitrification at the blastocyst stage on Day 5 does not adversely affect the development of human embryos and the ability of spindles to form and continue normal cell divisions. However, there was a significantly higher incidence of abnormal spindles in the vitrified group compared with the fresh group, notably of spindles with a focused and an unfocused pole as well as chromosome bridging and disorganized middle spindle fibres at telophase. Further investigation is warranted to elucidate the mitotic stages that are more vulnerable to damage during vitrification, the fate of the abnormal spindles and any potential effects that may be reflected on the chromosomal constitution of the developing blastocysts.