Examination of frozen cycles with replacement of a single thawed blastocyst

Effect of blastocyst shrinkage on assisted reproductive outcomes: a retrospective cohort study describing a new morphological evaluation of blastocyst pre-vitrification and post-warming

BACKGROUND

The failure of frozen-thawed blastocysts to re-expand adequately within a few hours after warming has been reported to have a negative impact on assisted reproductive technology (ART) outcomes. However, the extent to which this failure truly affects ART outcomes has not yet been presented in a manner that is easily understandable to medical practitioners and patients. This study aimed to assess the effects of blastocyst shrinkage on ART outcomes and determine a more effective morphological evaluation approach for use in clinical settings.

METHODS

This retrospective observational cohort study of frozen-thawed blastocyst transfer cycles was conducted from April 2017 to March 2022. Overall, 1,331 cycles were eligible for inclusion, of which 999 were good-quality blastocysts (GQB) and 332 were non-good-quality blastocysts (non-GQB). All frozen-thawed blastocyst transfer cycles performed during the specified study period were included in the study. Exclusion criteria were established to mitigate potential sources of bias as these cycles could impact implantations. We calculated rates and age-adjusted odds ratios of implantation, clinical pregnancy, ongoing pregnancy, and live birth of the re-expansion group, which showed sufficient expansion, and shrinkage group, which showed insufficient expansion. We also calculated the implantation, clinical pregnancy, ongoing pregnancy, and live birth rates of the re-expansion and shrinkage groups for each morphological scoring system parameter.

RESULTS

A reduced ART outcome was observed with use of blastocysts with shrinkage after vitrification/warming. The age-adjusted odds ratios for implantation, clinical pregnancy, ongoing pregnancy, and live birth were lower in the shrinkage group than in the re-expansion group.

CONCLUSIONS

This study examined the adverse effect of blastocyst shrinkage after warming and recovery culturing on reproductive outcomes in a clinically useful manner by retrospectively examining a substantial number of frozen-thawed embryo transfer cycles. The study findings can possibly reduce concerns regarding over- or under-estimation of blastocyst implantation by allowing providers and patients to refer to the data.

Standardization of Post-Vitrification Human Blastocyst Expansion as a Tool for Implantation Prediction

The increased use of vitrified blastocysts has encouraged the development of various criteria for selecting the embryo most likely to implant. Post-thaw assessment methods and timetables vary among investigators. We investigated the predictive value of well-defined measurements of human blastocyst re-expansion, following a fixed incubation period. Post-thaw measurements were taken exactly at 0 and 120 ± 15 min. Minimum and maximum cross-sectional axes were measured. Three groups were defined: Group 1: embryos that continued to shrink by 10 µm or more; group 2: embryos that ranged from −9 to +9 µm; and group 3: re-expansion of 10 µm or more. Patient and morphokinetic data were collected and integrated into the analysis. A total of 115 cases were included. The clinical pregnancy rate for group 1 was 18.9%; group 2, 27%; and group 3, 51.2% (p = 0.007). Pre-thaw morphologic grading and morphokinetic scores of the study groups did not reveal differences. p-values were 0.17 for the pre-thaw morphologic score, 0.54 for KID3, and 0.37 for KID5. The patients’ demographic and clinical data were similar. The clinical pregnancy rate correlated with the degree of thawed blastocyst re-expansion measured 2 h after incubation. This standardized measure is suggested as a tool to predict the potential of treatment success before embryo transfer.

Human frozen-thawed blastocyst morphokinetics observed using time-lapse cinematography reflects the number of trophectoderm cells

Recent studies reported morphokinetic indices for optimal selection of embryos in assisted reproductive technology (ART). The morphokinetics in blastocyst stage include the collapse and re-expansion rates after thawing. However, evaluation methods using these morphokinetics have not been established, mainly because the underlying molecular mechanisms remain unclarified. In this study, we focused on the relationship between these morphokinetic observation of the blastocyst behaviour and the number of cells constituting the blastocyst. We evaluated 38 surplus human frozen-thawed blastocysts using time-lapse cinematography and recorded their expansion, contraction, and hatching. A total of 28 blastocysts expanded in culture (cross-sectional area ≥ 5,000 π μm²). In comparison to the ones that did not, the expanded group presented significantly more number of inner cell mass (ICM) and trophectoderm (TE) cells, which eventually develop into the fetus and placenta, respectively (ICM: Expanded 10.2 ± 6.3 vs. Non-Expanded 6.0 ± 12.3, p < 0.05; TE: Expanded 165.7 ± 74.8 vs. Non-Expanded 57.0 ± 29.4, p < 0.05). Moreover, a positive correlation was found between the expansion rate (up to 4 h) and the number of TE cells (r = 0.558, p = 0.0021). Additionally, blastocysts that hatched had a significantly higher number of TE cells than those that did not (hatching 225.2 ± 61.2 vs. no hatching 121.1 ± 48.6, p < 0.0001). The number of TE cells per unit of cross-sectional area correlated negatively with the contraction time (r = –0.601, p = 0.0007). No correlation between the number of ICM cells and these morphokinetics was detected. In conclusion, our study demonstrates that different morphokinetics of frozen-thawed blastocysts reflect the number of TE cells. The differentiation of blastocysts containing sufficient TE cells would be beneficial for implantation and prognosis of a subsequent pregnancy. Thus, evaluation of these morphokinetics can be an effective method to screen good embryos for ART.

Artificial blastocyst collapse prior to vitrification significantly improves Na+/K+-ATPase-dependent post-warming blastocoel re-expansion kinetics without inducing endoplasmic reticulum stress gene expression in the mouse

Blastocoel expansion during embryo development is known to be reliant on the Na+/K+-ATPase pump, but little is known about the relative contribution of active (Na+/K+-ATPase pump) and facilitated diffusion (aquaporins) water transport during blastocoel re-expansion after vitrification. The aims of this study were to examine potential effects of artificial blastocoel collapse (ABC) on markers of embryo stress and the contribution of active and facilitated diffusion water transport mechanisms to blastocoel re-expansion. Day 5 mouse embryos were vitrified using either a standard protocol, laser pulse ABC, a hyperosmotic sucrose ABC protocol or both laser pulse and sucrose. Using real-time polymerase chain reaction, no differences were found in the gene expression of the endoplasmic reticulum (ER) stress markers activating transcription factor 4 (Atf4) or heat shock protein 90-alpha (Hsp90α) 2h after warming. Similarly, expression of the Na+/K+-ATPase pump gene, ATPase, Na+/K+ transporting, beta 1 polypeptide (Atp1b1) and protein did not differ between groups. Aquaporin 8 (Aqp8) gene expression was significantly lower in the laser+sucrose ABC group than in fresh controls, and aquaporin 3 (Aqp3) expression significantly higher in standard vitrified embryos compared with all other groups. Ouabain, a potent and specific Na+/K+-ATPase pump inhibitor, inhibited blastocoel re-expansion in both standard protocol- and laser ABC-vitrified embryos, reducing both groups to the same rate of re-expansion 3h after warming. These results demonstrate that ABC before vitrification does not alter mRNA or protein expression of Na+/K+-ATPase, or mRNA levels of ER stress genes Atf4 and Hsp90α. Activity of the pump may be increased in ABC embryos, with potential compensation by AQP3 when it is compromised.

A retrospective study of single frozen-thawed blastocyst transfer

OBJECTIVE

To study the clinical outcomes of single frozen-thawed blastocyst transfer cycles according to the hatching status of frozen-thawed blastocysts.

METHODS

Frozen-thawed blastocysts were divided into three groups according to their hatching status as follows: less-than-expanded blastocyst (≤EdB), hatching blastocyst (HgB), and hatched blastocyst (HdB). The female age and infertility factors of each group were evaluated. The quality of the single frozen-thawed blastocyst was also graded as grade A, tightly packed inner cell mass (ICM) and many cells organized in the trophectoderm epithelium (TE); grade B, several and loose ICM and TE; and grade C, very few ICM and a few cells in the TE. The clinical pregnancy and implantation rate were compared between each group. The data were analyzed by either t-test or chi-square analysis.

RESULTS

There were no statistically significant differences in average female ages, infertility factors, or the distribution of blastocyst grades A, B, and C in each group. There was no significant difference in the clinical pregnancy and implantation rate of each group according to their blastocyst grade. However, there was a significant difference in the clinical pregnancy and implantation rate between each group. In the HdB group, the clinical pregnancy and implantation rate were similar regardless of the blastocyst quality.

CONCLUSION

There was an effect on the clinical outcomes depending on whether the blastocyst hatched during single frozen-thawed blastocyst transfer. When performing single frozen-thawed blastocyst transfer, the hatching status of the frozen-thawed blastocyst may be a more important parameter for clinical outcomes than the quality of the frozen-thawed blastocyst.

Use of the CryoPredict algorithm to predict live birth from cryopreserved embryos

BACKGROUND

Currently, the viability of cryostored blastocysts that are subsequently re-warmed is determined via the percentage of cell survival. However, the large number of cells that forms the blastocyst can make this estimate difficult and unreliable. Studies have shown that fast re-expanding blastocysts have superior pregnancy rates.

AIM

To determine whether the degree and speed of blastocoele re-expansion following cryopreservation and warming correlate with rates of live birth.

MATERIALS AND METHODS

A retrospective cohort study of 757 frozen embryo transfer cycles over a 4-year period at Royal Prince Alfred Hospital, Sydney. Clinical and embryology notes were retrieved. Details regarding patient demographics, stimulation cycle from which embryos were derived, frozen embryo transfer cycles, embryology and pregnancy outcomes were recorded.

RESULTS

Female (P = 0.01) and male age (P = 0.02) at the time of embryo creation were inversely associated with live birth. Fertilisation method (P = 0.03), embryo type at cryopreservation (P = 0.009), embryo grade at cryopreservation (P < 0.0001), percentage of cell survival post-thaw (P < 0.0001) and the degree of re-expansion (P = 0.003) were the IVF and embryology factors significantly associated with live birth. A predictive model (CryoPredict) was created in order to individualise the probability that the transfer of a given embryo would result in live birth.

CONCLUSIONS

The degree and speed of blastocoele re-expansion postcryopreservation and subsequent warming can be used in conjunction with other parameters to predict live birth.

A randomized controlled trial comparing two vitrification methods versus slow-freezing for cryopreservation of human cleavage stage embryos

Purpose

To compare two different vitrification methods to slow freezing method for cryopreservation of human cleavage stage embryos. Design: Prospective randomised trial. Setting: University assisted reproduction centre. Patient(s): 568 patients (mean age 33.4 ± 5.2) from April 2009 to April 2011.

Methods

1798 supernumerary good-quality cleavage stage embryos in 645 IVF cycles intended to be cryopreserved were randomly allocated to three groups: slow freezing, vitrification with the Irvine® method, vitrification with the Vitrolife® method. Main Outcome Measure(s): Embryo survival and cleavage rates, implantation rate.

Results

A total of 1055 embryos were warmed, 836 (79.2 %) survived and 676 were finally transferred (64.1 %). Post-warming embryos survival rate was significantly higher after vitrification (Irvine: 89.4 %; Vitrolife: 87.6 %) than after slow freezing (63.8 %) (p < 0.001). No differences in survival rates were observed between the two vitrification methods, but a significant higher cleavage rate was observed using Irvine compared to Vitrolife method (p < 0.05). Implantation rate (IR) per embryo replaced and per embryo warmed were respectively 15.8 % (41/259) and 12.4 % (41/330) for Irvine, 17.0 % (40/235) and 12.1 % (40/330) for Vitrolife, 21.4 % (39/182) and 9.9 % (39/395) for slow-freezing (NS).

Conclusions

Both vitrification methods (Irvine and Vitrolife) are more efficient than slow freezing for cryopreservation of human cleavage stage embryos in terms of post-warming survival rate. No significant difference in the implantation rate was observed between the three cryopreservation methods.

The new Rapid-i carrier is an effective system for human embryo vitrification at both the blastocyst and cleavage stage

BACKGROUND

The Rapid-i is a new FDA cleared closed carrier for embryo vitrification. The cooling rate of - 1220°C/min is far lower than that reported with open vitrification systems such as the cryoloop (-15,000°C/min). Little published data is currently available on this device. This study presents our initial clinical data, as well as live birth outcomes, with the Rapid-i. The efficacy of this device for the cryopreservation of cleavage, as well as blastocyst stage human embryos is also analyzed. We further compare outcomes to those achieved with the cryoloop, an "open" vitrification system routinely used in our laboratory.

METHODS

Human embryos were vitrified at either the 8-10 cell stage or else the blastocyst stage. The vitrification protocol was: 7.5% DMSO/7.5% ethylene glycol (EG) (2-3 min) followed by incubation in 15% DMSO /15% EG (45 sec) before loading on the vitrification carrier. Cryoprotectant was removed during warming by sequential washes in 0.25 M and 0.125 M sucrose in culture medium. Clinical outcome data for frozen cycles between January 2011 and August 2012 were stratified according to carrier and cell stage. The student t-test and chi square test were used to compare results. P value of < 0.05 was considered significant.

RESULTS

A total of 486 vitrified-warmed embryos were assessed and 92% of them were transferred. The clinical pregnancy rate (CPR) and implantation rate (IR) with Rapid-i vitrified blastocysts were 59% and 49%, versus 47% and 37%, respectively for cleavage stage embryos. This was not statistically different from results with the cryoloop vitrified blastocysts (CPR 46%, IR 38%) nor the cleavage stage vitrified embryos (CPR 49%, IR 35%). To date, there have been 31 deliveries of 34 healthy infants from Rapid-i vitrified embryos, with another 12 pregnancies still on-going.

CONCLUSIONS

The Rapid-i offers an excellent alternative to existing open vitrification devices for embryo cryopreservation at the 8-10 cell stage as well as the blastocyst stage. Use of this type of "closed" sealed system that prevents direct contact between the embryos and liquid nitrogen reduces the potential risk of sample cross-contamination or infection. These preliminary data and live birth outcomes have paved the way toward transitioning to a closed vitrification system in our own IVF program.

A critical appraisal of cryopreservation (slow cooling versus vitrification) of human oocytes and embryos

BACKGROUND

Vitrification is now a commonly applied technique for cryopreservation in assisted reproductive technology (ART) replacing, in many cases, conventional slow cooling methodology. This review examines evidence relevant to comparison of the two approaches applied to human oocytes and embryos at different developmental stages.

METHODS

Critical review of the published literature using PubMed with particular emphasis on studies which include data on survival and implantation rates, data from fresh control groups and evaluation of the two approaches in a single setting.

RESULTS

Slow cooling is associated with lower survival rates and compromised development relative to vitrification when applied to metaphase II (MII) oocytes, although the vitrification results have predominantly been obtained using direct contact with liquid nitrogen and there is some evidence that optimal protocols for slow cooling of MII oocytes are yet to be established. There are no prospective randomized controlled trials (RCTs) which support the use of either technique with pronuclear oocytes although vitrification has become the method of choice. Optimal slow cooling, using modifications of traditional methodology, and vitrification can result in high survival rates of early embryos, which implant at the same rate as equivalent fresh counterparts. Many studies report high survival and implantation rates following vitrification of blastocysts. Although slow cooling of blastocysts has been reported to be inferior in some studies, others comparing the two approaches in the same clinical setting have demonstrated comparable results. The variation in the extent of embryo selection applied in studies can lead to apparent differences in clinical efficiency, which may not be significant if expressed on a 'per oocyte used' basis.

CONCLUSIONS

Available evidence suggests that vitrification is the current method of choice when cryopreserving MII oocytes. Early cleavage stage embryos can be cryopreserved with equal success using slow cooling and vitrification. Successful blastocyst cryopreservation may be more consistently achieved with vitrification but optimal slow cooling can produce similar results. There are key limitations associated with the available evidence base, including a paucity of RCTs, limited reporting of live birth outcomes and limited reporting of detail which would allow assessment of the impact of differences in female age. While vitrification has a clear role in ART, we support continued research to establish optimal slow cooling methods which may assist in alleviating concerns over safety issues, such as storage, transport and the use of very high cryoprotectant concentrations.

Frozen-thawed embryo transfer cycles: clinical outcomes of single and double blastocyst transfers

PURPOSE

To evaluate clinical outcomes of frozen-thawed embryo transfer cycles when one or two blastocysts are transferred.

METHODS

Retrospective chart review

RESULTS

Two hundred forty-three frozen blastocyst transfer (FBT) cycles were analyzed. Clinical pregnancy rate (50.4% vs. 34.7%), live birth rate (45.8% vs. 30.6%), and twin live birth rate (19.3% vs. 0) were significantly higher in the double versus single FBT group, respectively (p < 0.05). Prior fresh cycle success with same-cohort embryos did not predict outcome of FBT cycle. When the fresh cycle was unsuccessful, there still was a significant increase in twinning when two frozen-thawed blastocysts were transferred.

CONCLUSIONS

Transferring two blastocysts during an FBT cycle resulted in higher live birth and twin live birth rates. Single FBT provided acceptable pregnancy rates for couples seeking to avoid a multiple pregnancy or for those having a single blastocyst stored. Interestingly, the outcome of fresh cycle with same-cohort embryos did not influence the outcome of frozen-thawed cycle.

In vitro and in vivo viability of human blastocysts collapsed by laser pulse or osmotic shock prior to vitrification

PURPOSE

This study was designed to investigate whether artificial shrinkage, induced by a laser pulse or hyperosmotic sucrose solutions, improves in vitro survival and/or implantation of vitrified-warmed human expanded blastocysts.

METHODS

Before Cryotop vitrification, the blastocoelic cavity was collapsed either by a laser pulse or sucrose solutions. Non-treated blastocysts were used as control. Post-warm blastocyst survival and implantation after transfer were examined. Implantation rate outcome was retrospectively analyzed by morphological grading and developmental kinetics of post-warm blastocysts.

RESULTS

Survival rates in the three groups were high. Implantation rates in the laser-pulse group (59.7%) were comparable with those in the sucrose group (49.3%), and were significantly higher than those in the control group (34.2%). The proportion of blastocysts showing fast development tended to be higher when the blastocysts underwent artificial shrinkage treatment before vitrification. There was no clear correlation between morphology of post-warm blastocysts and implantation rate.

CONCLUSION

Artificial shrinkage treatment before vitrification is associated with an increased probability of fast-developing embryos, resulting in higher implantation rates.

Paternal effect on genomic activation, clinical pregnancy and live birth rate after ICSI with cryopreserved epididymal versus testicular spermatozoa

BACKGROUND

This study takes an in depth look at embryonic development, implantation, pregnancy and live birth rates with frozen epididymal and testicular sperm from obstructed (OA) and non-obstructed (NOA) patients.

METHODS

Paternal effect of sperm source on zygote formation, embryonic cleavage, and genomic activation were examined. Additional outcome parameters monitored were clinical pregnancy rate (CPR), implantation rate (IR) and live birth rate.

RESULTS

In this report, we retrospectively analyzed 156 ICSI cycles using cryopreserved epididymal sperm (ES; n = 77) or testicular sperm (TESE; n = 79). The developmental potential of embryos did not appear to be influenced by the type of surgically retrieved sperm. The average number of blastomeres observed on Day 3 was not different among different groups; 7.5 +/- 1.7 (ES), 7.6 +/- 2.1 (TESE-OA) and 6.5 +/- 2.3 (TESE-NOA). Compaction and blastulation rates, both indicators of paternal genomic activation, were similar in embryos derived from ICSI with ES or TESE from OA as well as NOA men. The only parameter significantly affected in NOA-TESE cases was the fertilization rate. CPR and IR with cryopreserved TESE (TESE-OA 59%, 34%, and TESE-NOA 37%, 20%) were also not statistically different, from that achieved with cryopreserved ES (61% and 39%). Live birth rates also appeared to be independent of sperm type. The 87 clinical pregnancies established using cryopreserved TESE and ES, resulted in the birth of 115 healthy infants. No congenital anomalies were noted.

CONCLUSION

Zygotic activation seems to be independent of sperm origin and type of azoospermia.