Current aspects of blastocyst cryopreservation

A comparative study of post-warming survival rates and clinical outcomes of human blastocysts vitrified/warmed by CryoTouch and Cryotop methods

OBJECTIVE

Advances in embryo culture conditions and the development of vitrification as a revolutionary cryopreservation method have allowed for routine use of blastocyst transfer in assisted reproduction technology (ART) cycles. Several vitrification/warming media and devices have been introduced for commercial use so far. The aim of this retrospective study was to compare post-warming survival rates and clinical outcomes of human blastocysts vitrified/warmed by two different commercial methods (CryoTouch and Cryotop) during ART cycles.

METHODS

This retrospective study assessed a total of 50 frozen embryo transfer (FET) cycles conducted on 56 warmed blastocysts between January 2018 and December 2020. Post-warming blastocyst survival rates and clinical outcomes including clinical pregnancy and live birth rates were calculated after single blastocyst transfer cycles.

RESULTS

The results revealed no significant differences between two groups in post-warming survival rate (p-value=0.8381), clinical pregnancy rate (p-value=0.8157) and live birth rate (p-value=0.7041).

CONCLUSIONS

Post-warming survival rates and clinical outcomes were comparable with no significant difference in blastocysts vitrified/warmed by CryoTouch and Cryotop commercial methods.

Preimplantation genetic testing for monogenic diseases: a Brazilian IVF centre experience

OBJECTIVE

To describe the cases of preimplantation genetic testing for monogenic diseases (PGT-M) in fertile couples who had undergone intracytoplasmic sperm injection (ICSI) cycles in a Brazilian in vitro fertilisation (IVF) centre and determine whether these cases were different from those reported from the European Society of Human Reproduction and Embryology (ESHRE).

METHODS

This retrospective collection included data obtained from ICSI-PGT-M cycles between 2011 and 2016. The disease indication, number of biopsied embryos, biopsy stage, diagnosed and affected embryos, and cycles with embryo to transfer as well as implantation, pregnancy and miscarriage rates were analysed and compared to cycles without genetic diagnosis (PGT) and with ESHRE PGD Consortium collection XIV-XV.

RESULTS

From 5,070 cycles performed, 72 had indications for PGT-M. The most common time for biopsy was cleavage-stage; 93% of the embryos had a diagnostic result, 59.4% of which were genetically transferable, resulting in 68% of the cycles with transferred embryos, a 22.1% implantation rate, and a 28.6% pregnancy rate. No differences in clinical outcomes of cycles with PGT-M or without PGT were observed. The day of biopsy and diagnostic success as well as implantation, pregnancy and miscarriage rates were similar to ESHRE collection.

CONCLUSIONS

Although the proportion of cases with PGT-M was low, its efficacy was similar to what was reported in the European collection and represents a viable alternative for families at risk of transmitting a genetic disorder to their offspring. The main difference between our and ESHRE collection were the disease indications, which reflected the admixed, multi-ethnic Brazilian population.

Embryo pooling: a promising strategy for managing insufficient number of embryos in preimplantation genetic diagnosis

This retrospective study evaluated the embryo pooling strategy for managing insufficient number of embryos in preimplantation genetic diagnosis (PGD) through serial vitrification of cleavage-stage embryos from consecutive cycles, and simultaneous blastocysts biopsy in combination with blastocysts obtained in ultimate fresh cycle. A retrospective analysis of the cumulative pregnancy rate of 68 patients underwent cleavage-stage embryos accumulation (Embryo Pooling Group) and 94 patients underwent one stimulation cycle (Control Group) over a 2-year period were conducted. The blastocyst formation rate was comparable between the consecutive cycles and the ultimate cycle in embryo pooling group (56.0 versus 62.0%, p = .078). No significant difference existed between twice-vitrified and once-vitrified warmed blastocysts with respect to implantation rate (50.8 versus 46.3%, p = .658). The implantation rate and cumulative pregnancy rate of embryo pooling group were 49.0 and 67.6%, respectively, which were statistically comparable to the corresponding values of 48.9 and 73.4% obtained in control group. Our study suggests that in patients undergoing ICSI-PGD who do not reach enough embryos in a single stimulation cycle, pooling embryos from consecutive ovarian stimulation cycles is a promising strategy, which can render a cumulative pregnancy rate comparable to those patients who only require one stimulation cycle.

Long Cut Straw Provides Stable the Rates of Survival, Pregnancy and Live Birth for Vitrification of Human Blasotcysts

Most of the commercial devices for vitrification are directly immersed into the warming solution (WS) for increasing of warming rate. However, the previous modified cut standard straw (MCS) which has reported is difficult to immerse into the WS. The aim of this study was to investigate whether the long cut straw (LCS) could be useful as a stable tool for vitrified-warmed human blastocysts. A total of 138 vitrified-warmed cycles were performed between November 2013 and November 2014 (exclusion criteria: women ≥38 years old, poor responder, surgical retrieval sperm, and severe male factor). The artificial shrinkage was conducted using 29-gauge needles. Ethylene glycol and dimethyl sulfoxide (7.5% and 15% (v/v)) were used as cryoprotectants. Freezing and warming were conducted using the LCS tool. The cap of LCS was removed using the forceps in the liquid nitrogen (LN₂) and then directly immersed into the first WS for 1 min at 37℃ (1 M sucrose). Only re-expanded blastocysts were transferred after it was cultured in sequential media for 18-20 h. A total of 294 blastocysts were warmed, and all were recovered (100%). Two hundred eighty-five embryos were survived (96.9%). The vitrifiedwarmed blastocysts of all patients were transferred without any cancellation. We were able to achieve a reasonable implantation (24.2%), following by clinical pregnancy (36.2%), which then continued to ongoing pregnancy (36.2%), and live birth (31.2%). Using LCS is achieved the acceptable rates of survival, pregnancy and live birth. Therefore, the LCS could be considered as a stable and simple tool for human embryo vitrificaton.

The endometrial preparation for frozen-thawed euploid blastocyst transfer: a prospective randomized trial comparing clinical results from natural modified cycle and exogenous hormone stimulation with GnRH agonist

PURPOSE

The aim of the study was to evaluate two methods of endometrial preparation for frozen-thawed single euploid blastocyst transfer: modified natural and artificial cycle with GnRH-agonist pituitary suppression.

METHODS

In this prospective, controlled randomized trial, a total of 236 patients undergoing infertility treatment were randomized in 1:1 ratio; 118 received a frozen-thawed single euploid blastocyst transfer in a modified natural cycle and 118 in an artificial cycle with GnRH-agonist pituitary suppression. In the artificial protocol, GnRH-agonist combined with estradiol valerate was administered. In the natural protocol, only final oocyte maturation was induced using human chorionic gonadotropin administration. The primary end-points were the clinical pregnancy and implantation rates; the secondary end-points were the cost-benefit in terms of drug cost and the number of visits and the woman psychological distress caused by the treatment.

RESULTS

No significant differences were found in clinical pregnancy, implantation, and miscarriage rates between protocols. The number of clinical and ultrasound controls and the number of laboratory dosages and venous samplings were similar in both study groups. No significant differences were found between the groups in the anxiety and depression values before the start of treatment, on the days of progesterone administration, the blastocyst transfer, and pregnancy test.

CONCLUSIONS

The findings of this study evidence that in case of frozen-thawed single euploid blastocyst transfer, both protocols are equally effective in terms of clinical outcomes, cost-benefit, and patient compliance. The choice of endometrial preparation protocol should be based on women menstrual and ovulatory characteristics or otherwise on patient need for cycle planning.

TRIAL REGISTRATION

www.clinicaltrials.gov with number NCT02378584.

Pregnancy outcomes of blastocysts cultured overnight after thawing

PURPOSE

To compare embryo quality and outcomes of blastocysts thawed and transferred the same day with those thawed and cultured overnight before transfer.

METHODS

In this retrospective study, patients with infertility who underwent thawed embryo transfer (TET) the same day as thawing (0TET group) and those that received TET after embryos were thawed and cultured overnight before transfer (1TET group) were enrolled. Univariable and multivariable logistic regression were performed to detect the factors associated with the clinical pregnancy rate (CPR), implantation rate, miscarriage rate, and multiple pregnancy rate.

RESULTS

A total of 489 patients (489 cycles) were included with 234 in the 0TET group and 255 in the 1TET group. There were no significant differences between the two groups with respect to age, body mass index (BMI), basal FSH and estradiol (E2) level, and causes of infertility (all, p > 0.05). There were no significant differences in the CPR, implantation rate, miscarriage rate, or multiple pregnancy rate between the two groups (all, p > 0.05), and this finding was irrespective of the endometrial preparation method.

CONCLUSIONS

Pregnancy outcomes are the same for blastocysts thawed and cultured overnight 1 day before transfer and those thawed and transferred on the same day.

Influence of blastocysts morphological score on pregnancy outcomes in frozen-thawed blastocyst transfers: a retrospective study of 741 cycles

The influence of inner cell mass (ICM) and trophectoderm (TE) score on pregnancy outcomes in frozen-thawed blastocyst transfer cycles was analyzed. A retrospective analysis of 741 cycles of frozen-thawed blastosysts transfer was performed. All cycles were divided into four groups based on the number and morphological score of blastocysts: S-ICM B/TE B group (n=91), the single blastocyst transfer of ICM B and TE B; D-ICM B/TE B group (n=579), double blastocysts transfer of ICM B/TE B; D-ICM B/TE C group (n=35), double blastocysts transfer of ICM B/TE C; and D-ICM C/TE B group (n=36), double blastocysts transfer of TE B/ICM C. The pregnancy outcomes were compared among the four groups. As compared with D-ICM B/TE C group, the clinical pregnancy rate, implantation rate and multiple pregnancy rate were increased in D-ICM B/TE B group (74.96% vs. 57.14%, 57.43% vs. 37.14%, and 48.62% vs. 25%, respectively, P<0.05 for all). Clinical pregnancy rate and implantation rate in D-ICM B/TE B group were also higher than in D-ICM C/TE B group (74.96% vs. 50%, and 57.43% vs. 33.33%, both P<0.05). Multivariable Logistic regression analysis indicated that ICM score was a better predictive parameter for clinical pregnancy (OR=3.05, CI 1.70-5.46, P<0.001), while the trophectoderm score was a better one for early abortion (OR=0.074, CI 0.03-0.19, P<0.001). Clinical pregnancy rate and multiple pregnancy rate in S-ICM B/TE B group were significantly lower than those in D-ICM B/TE B group (46.15% vs. 74.96%, and 2.38% vs. 48.62%, both P<0.05), but there was no significant difference in the implantation rate between the two groups. It was suggested that the higher score of ICM and TE may be indicative of the better pregnancy outcomes. The ICM score is a better predictor of clinical pregnancy than TE, while TE score is a better one in predicting early abortion. Single ICM B/TE B blastocyst transfer in frozen-thawed cycles can also get satisfactory pregnancy outcomes.

Current issues in medically assisted reproduction and genetics in Europe: research, clinical practice, ethics, legal issues and policy. European Society of Human Genetics and European Society of Human Reproduction and Embryology

In March 2005, a group of experts from the European Society of Human Genetics and European Society of Human Reproduction and Embryology met to discuss the interface between genetics and assisted reproductive technology (ART), and published an extended background paper, recommendations and two Editorials. Seven years later, in March 2012, a follow-up interdisciplinary workshop was held, involving representatives of both professional societies, including experts from the European Union Eurogentest2 Coordination Action Project. The main goal of this meeting was to discuss developments at the interface between clinical genetics and ARTs. As more genetic causes of reproductive failure are now recognised and an increasing number of patients undergo testing of their genome before conception, either in regular health care or in the context of direct-to-consumer testing, the need for genetic counselling and preimplantation genetic diagnosis (PGD) may increase. Preimplantation genetic screening (PGS) thus far does not have evidence from randomised clinical trials to substantiate that the technique is both effective and efficient. Whole-genome sequencing may create greater challenges both in the technological and interpretational domains, and requires further reflection about the ethics of genetic testing in ART and PGD/PGS. Diagnostic laboratories should be reporting their results according to internationally accepted accreditation standards (International Standards Organisation - ISO 15189). Further studies are needed in order to address issues related to the impact of ART on epigenetic reprogramming of the early embryo. The legal landscape regarding assisted reproduction is evolving but still remains very heterogeneous and often contradictory. The lack of legal harmonisation and uneven access to infertility treatment and PGD/PGS fosters considerable cross-border reproductive care in Europe and beyond. The aim of this paper is to complement previous publications and provide an update of selected topics that have evolved since 2005.

Genomic DNA in human blastocoele fluid

IVF often requires embryo cryopreservation through vitrification. During the vitrification process, the embryos can be collapsed by withdrawing the blastocoele fluid. The metabolomic profile of blastocoele fluid has been recently investigated by high-performance liquid chromatography-electrospray ionization-mass spectrometry to provide metabolite information that can help estimations of implantation efficiency. However, the presence of embryo DNA in blastocoele fluid has not been reported to date. This study shows using real-time PCR that genomic DNA was present in about 90% of blastocoele fluid samples harvested during the vitrification procedure. Moreover, the potential for determining embryo sex directly from blastocoele fluid is demonstrated by amplifying the multicopy genes TSPY1 (on the Y chromosome) and TBC1D3 (on chromosome 17). This opens up the possibility of screening embryos from couples carrying an X-linked disorder to identify male embryos at high risk of disease. The application of whole-genome amplification technologies to fluid samples is also shown to be feasible, potentially allowing more comprehensive genetic tests. As proof of principle, microarray comparative genomic hybridization was attempted to confirm the sex of embryos as well as detect several aneuploidies. However, further studies are needed to validate this approach and confirm that the accuracy is sufficient for diagnostic purposes.

Comparable clinical outcomes and live births after single vitrified-warmed and fresh blastocyst transfer

Selective single-blastocyst transfer (SBT) in fresh cycles has been effective in reducing multiple pregnancies. However, we do not know whether this successful strategy of fresh transfer cycles is suitable for cryopreserved cycles. The present study was undertaken to evaluate the feasibility and value of SBT in vitrified-warmed cycles. Clinical pregnancy rate (CPR) was similar with vitrified and fresh SBT (46.61% versus 52.15% respectively). Of the pregnant patients, monozygotic twin, miscarriage and ectopic pregnancy rates were similar with vitrified and fresh SBT. For the newborns, no significant difference was observed in live birth, low birthweight, premature delivery and birth defects rates between vitrified and fresh SBT. With respect to the quality of transferred blastocysts (from BB to AA), a similar CPR and miscarriage rate was obtained for both vitrified and fresh SBT when a similar blastocyst cohort graded ≥ 3BB was transferred. The data show that vitrified SBT is an effective means of reducing multiple pregnancy and that comparable clinical outcomes and live births are achieved if single blastocysts graded ≥ 3BB are transferred for both vitrified and fresh SBT. These data should encourage clinics to evaluate their embryo transfer policy and adopt vitrified SBT as everyday practice. Selective single-blastocyst transfer in fresh cycles has been an effective method to reduce the multiple pregnancies. However, due to a lack of adequate studies, we do not know whether this successful strategy in fresh transfer cycles is suitable in cryopreserved cycles. The present study was undertaken to explore the feasibility and value of single-blastocyst transfer in vitrified-warmed cycles. We found that single-blastocyst transfer in vitrified-warmed cycles is an effective means of reducing multiple pregnancy, and comparable clinical outcomes and live births were achieved if single blastocysts graded ≥ 3BB were transferred for both vitrified-warmed and fresh blastocyst transfer. These data should encourage clinics to evaluate their embryo transfer policy and adopt single-blastocyst transfer in cryopreserved cycles as their everyday practice.

Optimal condition of vitrification method for cryopreservation of human ovarian cortical tissues

AIM

In order to find the optimal exposure time of cryoprotectant, we performed a comparison of vitrification versus slow freezing according to the degree of normal morphology and apoptosis of human ovarian follicles.

MATERIALS AND METHODS

Eleven patients aged 20-41 years who underwent operative laparoscopy for benign ovarian cysts or cesarean section were enrolled in this study. We carried out a prospective parallel comparison of survival and morphology of follicles after freezing (slow freezing and vitrification) and thawing. The ovarian strips were vitrified with two-step exposure to equilibration and vitrification solutions at room temperature. After various exposure times of cryoprotectant solution (5 min, 10 min, and 20 min, respectively), cryoprotectant-filled cryovials with pretreated cortical tissues were immediately plunged into liquid nitrogen.

RESULTS

In total, 336 follicles were analyzed by light microscopy to assess the morphology. The distribution of follicles was as follows: primordial, primary, and secondary follicles were 55.7% (187/336), 36.9% (124/336), and 7.4% (25/336), respectively. Vitrification in the 10-min exposure group preserved the follicles most effectively (ratio of grade 1 follicle: 3.6%, 34.7%, 13.8%, and 20.0% in the 5-min, 10-min, 20-min, and slow-freezing groups, respectively). Fewer terminal-deoxynucleotidyl-transferase-dUTP-nick-end-labeling-positive cells were found in vitrification in the 10-min equilibrium group compared with the other cryopreserved-thawed groups (52.1%, 31.5%, 53.1%, and 46.7% in the 5-min, 10-min, 20-min, and slow-freezing groups, respectively). The stromal cells were also better preserved in the 10-min group than the others (P < 0.05).

CONCLUSIONS

The 10-min exposure group for vitrification showed better results compared with other conditions and the slow-freezing group.

Use of the natural cycle and vitrification thawed blastocyst transfer results in better in-vitro fertilization outcomes : cycle regimens of vitrification thawed blastocyst transfer

PURPOSE

To compare the IVF outcomes of vitrification-thawed blastocyst transfer cycles utilizing different endometrial preparation methods.

METHODS

We retrospectively assessed IVF outcomes in 611 patients (648 cycles) who underwent blastocyst frozen embryo transfer (FET) between January 2007 and December 2009. All embryos had been cryopreserved by a vitrification method following a previous IVF cycle. Patients were prepared for transfer by using either the natural cycle (n = 310/Group 1), the natural cycle with ovulation induction employing human chorionic gonadotropin (n = 134/Group 2), or a hormonally manipulated artificial cycle with estrogen and progesterone supplementation (n = 204/Group 3).

RESULTS

Multivariate logistic regression analysis showed a significant difference in clinical pregnancy rate between Groups 3 (30.4%) and 1 (41.9%) (odds ratio [OR], 0.567; 95% confidence interval [CI], 0.379-0.847, P = 0.006) whereas the difference between Groups 2 and 1 was not significant (41.8% vs. 41.9%; OR, 0.683; 95% CI, 0.435-1.073; P = 0.098). Other significant variables affecting clinical pregnancy rate were the number of embryos transferred, the grade of transferred embryos, and maximal endometrial thickness.

CONCLUSION

The results showed that, using vitrification-thawed blastocyst transfer, employment of natural cycles with or without hCG treatment was associated with better outcomes than was the use of hormonally manipulated cycles.

Whole sheep ovary cryopreservation: evaluation of a slow freezing protocol with dimethylsulphoxide

PURPOSE

To evaluate a slow freezing method for whole ovary cryopreservation by evaluating effects of added cryoprotectant.

METHODS

Sheep ovaries were isolated during surgery, flushed with either Ringer-Acetate or dimethylsulphoxide and cryopreserved by slow freezing. After rapid thawing, viability was assessed by ovarian in vitro perfusion, cell culture, histology and fluorescent live-dead assay.

RESULTS

Production of cyclic AMP and progesterone was slightly higher in the dimethylsulphoxide group. Cultured ovarian cells from dimethylsulphoxide-preserved ovaries secreted larger amounts of progesterone than cells from Ringer-Acetate preserved. Light microscopy of ovarian biopsies obtained after perfusion, revealed well-preserved tissue in the dimethysulphoxide group but not in the Ringer-Acetate group. The density of small follicles and ovarian cell viability were higher in dimethysulphoxide ovaries compared to Ringer-Acetate ovaries.

CONCLUSIONS

Equilibrium with its protective effect can be achieved by slow freezing protocol, with an additional protective effect by the presence of dimethylsulphoxide.

Vitrification in assisted reproduction: myths, mistakes, disbeliefs and confusion

The purpose of this work is to update embryologists and clinicians on different approaches in human oocyte and embryo cryopreservation, by clarifying some misunderstandings and explaining the underlying reasons for controversial opinions. The work is based on literature review and critical analysis of published papers or conference abstracts during the last 24 years, with special focus on the last 3 years. Due to the latest advancements in techniques, cryopreservation now offers new perspectives along with solutions to many demanding problems, and has developed from a backup procedure to a successful alternative that is an indispensable constituent of assisted reproductive techniques. However, this progress is not free from controversies, at some points is rather serendipitous, and many factors, including human ones, hamper the selection and widespread application of the most efficient technique for the given task. A better understanding of the basic features of the two rival approaches (slow-rate freezing and vitrification), a clarification of terms and technical details, and a balanced, pragmatic evaluation of possible risks and potential, or definite, gains are required to accelerate advancement. Alternatively, the increasing flow of patients to the few assisted reproduction clinics and countries that are highly successful in this field will enforce the required changes in methodology and mentality worldwide.

Vitrification of human embryos subjected to blastomere biopsy for pre-implantation genetic screening produces higher survival and pregnancy rates than slow freezing

PURPOSE

Cryopreservation of blastocysts, especially those subjected to the trauma due to blastomere biopsy for the purposes of pre-implantation genetic screening (PGS), requires significant optimization. Laboratory and clinical outcomes were compared to determine the effect of two different cryopreservation techniques on the development of human pre-implantation embryos that underwent blastomere biopsy and blastocoel drainage prior to cryopreservation.

DESIGN

Retrospective clinical study.

PATIENT(S)

Women who requested cryotransfer of supernumerary blastocysts were analyzed by FISH.

RESULTS

The main outcome measures were post-thaw survival (SR), pregnancy (PR), and implantation (IR). The SR of slowly frozen blastocysts was 83% compared to 97% for vitrified blastocysts. In 160 cases where biopsied embryos were cryotransferred, the results for slowly frozen versus vitrified blastocysts were: SR (71% vs. 95%), PR (23% vs. 37%), and IR (26% vs. 36%, P < 0.05), respectively.

CONCLUSION

The results revealed that vitrified blastocysts provided higher SR, PR and IR as compared to slowly frozen counterparts.

Vitrification of mouse embryos at 2-cell, 4-cell and 8-cell stages by cryotop method

PURPOSE

The objective of this study was to investigate the effects of vitrification on the preimplantation developmental competence of mouse 2-cell, 4-cell and 8-cell stage embryos.

METHODS

Mouse 2-cell, 4-cell and 8-cell stage embryos were cryopreserved using the cryotop vitrification method and subsequently warmed on a later date. The embryos were then assessed by their morphology, blastocyst formation and hatching rates. Additionally, trophectoderm (TE) and inner cell mass (ICM) cell numbers were compared in hatched blastocysts from the control and experimental groups.

RESULTS

Vitrified embryos at the 2-cell, 4-cell and 8-cell stages appeared morphologically normal after warming. The overall survival rate of vitrified embryos at various stages after warming was 96.7% and there were no significant differences among 2-cell stage (96.0%), 4-cell stage (96.8%) and 8-cell stage (97.1%) embryos (P > 0.05). The blastocyst formation rate (69.4%) and hatching rate (52.6%) of vitrified 2-cell embryos were significantly lower than that from the control group and vitrified 8-cell embryos (P < 0.05). In the vitrified 4-cell embryo group, the blastocyst formation rate (90.3%) was similar to the 8-cell group (91.2%), but the hatching rate (60.0%) was significantly lower than that of the non-vitrified control ( 84.1%) and vitrified 8-cell embryo (78.4%) groups (P < 0.05). When further development to the fully hatched blastocyst stage was compared, hatched blastocysts derived from vitrified 2-cell, 4-cell and 8-cell embryos had significantly lower cell counts both in the ICM and TE, as compared to fresh blastocysts (P < 0.05). Among the vitrified 2-cell, 4-cell and 8-cell embryo groups, there were no significant differences in the cell counts of ICM and TE (P > 0.05).

CONCLUSIONS

Although cryotop vitrification was suitable for the cryopreservation of mouse embryos from the 2-cell stage, 4-cell stage and 8-cell stage without significant loss of survival, vitrification had an adverse effect on the development of 2-cell embryos. Mouse embryos at the 8-cell stage had the best tolerance for vitrification and would yield the highest level of post-vitrification developmental competence among early cleavage stage embryos. Nevertheless, it is unclear how these findings can be extrapolated to human embryos.

Human oocyte cryopreservation: comparison between slow and ultrarapid methods

The success of reproductive technologies is facilitated by the cryopreservation of embryos and gametes. In Italy, where legislation prohibits zygote and embryo cryopreservation, clinics have extensively introduced oocyte cryopreservation. Two different strategies of oocyte cryopreservation are available: slow freezing or ultrarapid cooling (vitrification). Although the results are very encouraging with both methods, there is still controversy regarding both the procedure itself and the most suitable method to use. This study reports the routine application of the two different oocyte cryopreservation methods in programmes running in two consecutive periods. The study centre carried out 286 thawing cycles for a total of 1348 thawed oocytes cryopreserved by the slow-freezing method and 59 warming cycles for a total of 285 warmed oocytes cryopreserved by vitrification. Comparison of the outcomes obtained with the slow-freezing method versus vitrification in women who underwent IVF for infertility showed survival, fertilization, pregnancy and implantation rates of 57.9% versus 78.9% (P < 0.0001), 64.6% versus 72.8% (P = 0.027), 7.6% versus 18.2% (P = 0.021) and 4.3% versus 9.3% (P = 0.043) respectively. These results suggest that oocyte vitrification is associated with a better outcome than the slow-freezing method.

Factors affecting the outcome of human blastocyst vitrification

With single blastocyst transfer practice becoming more common in ART, there is a greater demand for a convenient and reliable cryostorage of surplus blastocysts. Vitrification has emerged in the last decade as an alternative promising substitute for slow freezing. Blastocysts represent a unique challenge in cryostorage due to their size, multicellular structure and presence of blastocoele. The continuous acquisition of experience and introduction of many different technological developments has led to the improvement of vitrification as a technology and improved the results of its application in blastocyst cryostorage. The current information concerning safety and efficacy of the vitrification of blastocysts will be reviewed along with the variables that can impact the outcome of the procedure.

Live offspring from vitrified blastocysts derived from fresh and cryopreserved ovarian tissue grafts of adult mice

Ovarian tissue cryopreservation and transplantation can be used to preserve fertility for cancer patients. In this study, we assessed the viability and function of ovarian tissue from adult mice that was cryopreserved by solid surface vitrification or traditional slow-cooling using variousin vitroandin vivotechniques, including allotransplantation,in vitrooocyte maturation, embryo culturein vitro, blastocyst cryopreservation, embryo transfer, and development. The importance of cumulus cells for oocyte maturation, fertilization, and embryo development was investigated. Graft recovery, follicle survival, and oocyte retrieval was similar in control, vitrified, and slow-cooled groups. High rates of oocyte maturation, cleavage, and blastocyst formation were achieved, with no significant differences between the control, vitrified or slow-cooled ovarian tissue grafts. The presence of cumulus cells was important for oocyte maturation, fertilization, and subsequent development. Cumulus–oocyte complexes with no surrounding cumulus cells (N-COCs) or with an incomplete layer (P-COCs) had significantly lower rates of oocyte maturation and blastocyst formation than cumulus–oocyte complexes with at least one complete layer of cumulus cells (F-COCs; maturation rate: 63, 78 vs 94%; blastocyst rate: 29, 49 vs 80%). Live births were achieved using vitrified blastocysts derived from oocytes taken from vitrified and slow-cooled ovarian tissue heterotypic allografts. Successful production of healthy offspring from these vitrified blastocysts suggests that this technique should be considered as a useful stage to pause in the assisted reproduction pathway. This provides an alternative protocol for restoring fertility and offering cancer patients a better indication of their chances of pregnancy and live birth.

Bibliography. Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 February 2008 and 31 January 2009 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

Approaches to improve the diagnosis and management of infertility

BACKGROUND Recent advances in our understanding of the causes of infertility and of assisted reproductive technology (ART) have led to the development of complex diagnostic tools, prognostic models and treatment options. The Third Evian Annual Reproduction (EVAR) Workshop Meeting was held on 26-27 April 2008 to evaluate evidence supporting current approaches to the diagnosis and management of infertility and to identify areas for future research efforts. METHODS Specialist reproductive medicine clinicians and scientists delivered presentations based on published literature and ongoing research on patient work-up, ovarian stimulation and embryo quality assessment during ART. This report is based on the expert presentations and subsequent group discussions and was supplemented with publications from literature searches and the authors' knowledge. RESULTS It was agreed that single embryo transfer (SET) should be used with increasing frequency in cycles of ART. Continued improvements in cryopreservation techniques, which improve pregnancy rates using supernumerary frozen embryos, are expected to augment the global uptake of SET. Adaptation and personalization of fertility therapy may help to optimize efficacy and safety outcomes for individual patients. Prognostic modelling and personalized management strategies based on individual patient characteristics may prove to represent real progress towards improved treatment. However, at present, there is limited good-quality evidence to support the use of these individualized approaches. CONCLUSIONS Greater quality control and standardization of clinical and laboratory evaluations are required to optimize ART practices and improve individual patient outcomes. Well-designed, good-quality studies are required to drive improvements to the diagnosis and management of ART processes.

Vitrification versus slow freezing gives excellent survival, post warming embryo morphology and pregnancy outcomes for human cleaved embryos

PURPOSE

The objective of this retrospective study was to evaluate the efficacy of vitrification and slow freezing for the cryopreservation of human cleavage stage embryos in terms of post-warming survival rate, post-warming embryo morphology and clinical outcomes.

METHODS

The embryos of 305 patients at cleavage stages were cryopreserved either with vitrification (153 patients) or slow-freezing (152 patients) methods. After warming; the survival rate, post-warmed embryo morphology, clinical pregnancy and implantation rates were evaluated and compared between the two groups.

RESULT(S)

In the vitrification group versus slow freezing group, the survival rate (96.9% vs. 82.8%) and the post-warmed excellent morphology with all blastomeres intact (91.8% vs. 56.2%) were higher with an odds ratio of 6.607 (95% confidence interval; 4.184-10.434) and 8.769 (95% confidence interval; 6.460-11.904), respectively. In this group, the clinical pregnancy rate (40.5% vs. 21.4%) and the implantation rate (16.6% vs. 6.8%) were also higher with an odds ratio of 2.427 (95%confidence interval; 1.461-4.033) and 2.726 (95% confidence interval; 1.837-4.046), respectively.

CONCLUSION(S)

Vitrification in contrast to slow freezing is an efficient method for cryopreservation of human cleavage stage embryos. Vitrification provides a higher survival rate, minimal deleterious effects on post-warming embryo morphology and it can improve clinical outcomes.

Elective single embryo transfer: guidelines for practice British Fertility Society and Association of Clinical Embryologists

Assisted conception treatment is the single most important cause in the increase in multiple pregnancy and births over the last 25 years. Multiple births are associated with significant peri natal morbidity and mortality. Europe has led the way in reducing multiple births by widespread adoption of an elective single embryo policy, which in Belgium is linked to an increase in state funding. Randomized controlled trials suggest that an eSET policy must include the ability to cryopreserve and transfer any remaining quality embryos to obtain parity with a double embryo transfer. This document provides a review of the available evidence with guidelines for practice, to help facilitate the introduction of an eSET policy in the UK.

Successful vitrification of human amnion-derived mesenchymal stem cells

BACKGROUND

A cryopreservation protocol for human amnion-derived mesenchymal stem cells (HAMs) is required because these cells cannot survive for long periods in culture. The aim of this study was to determine whether vitrification is a useful freezing method for storage of HAMs.

METHODS

HAMs were cryopreserved using vitrification method. The morphology and viability of thawed HAMs was evaluated by Trypan Blue staining. The expression of several embryonic stem cell (ESC) markers was evaluated using flow cytometry, RT-PCR and immunocytochemistry. Von Kossa, Oil Red O and Alcian Blue staining were used to asses the differentiation potential of thawed HAMs.

RESULTS

The post-thawing viability of HAMs was 84.3 +/- 3.2% (Mean +/- SD, n = 10). The thawed HAMs showed morphological characteristics indistinguishable from the non-vitrified fresh HAMs. The expression of surface antigens (strong positive for CD44, CD49d, CD59, CD90, CD105 and HLA-ABC; weak positive for HLA-G; negative for CD31, CD34, CD45, CD106, CD117 and HLA-DR) and the expression of ESC markers [CK18, fibroblast growth factor-5, GATA-4, neural cell adhesion molecule, Nestin, Oct-4, stem cell factor, HLA-ABC, Vimentin, bone morphogenetic protein (BMP) 4, hepatocyte nuclear factor 4 alpha (HNF-4 alpha), Pax-6, alpha-fetoprotein, Brachyury, BMP-2, TRA-1-60, stage-specific embryonic antigen (SSEA-3, SSEA-4)] were maintained in the vitrified-thawed HAMs. The thawed HAMs retained ability to differentiate into osteoblasts, adipocytes and chondrocytes under appropriate culture conditions.

CONCLUSIONS

Our results suggest that vitrification is a reliable and effective method for cryopreservation of HAMs.