Cryopreservation of human embryos by vitrification or slow freezing: a systematic review and meta-analysis

A randomized assessor-blind trial comparing highly purified hMG and recombinant FSH in a GnRH antagonist cycle with compulsory single-blastocyst transfer

OBJECTIVE

To compare the efficacy and safety of highly purified menotropin (hphMG) and recombinant FSH (rFSH) for controlled ovarian stimulation in a GnRH antagonist cycle with compulsory single-blastocyst transfer.

DESIGN

Randomized, open-label, assessor-blind, parallel groups, multicenter, noninferiority trial.

SETTING

Twenty-five infertility centers in seven countries.

PATIENT(S)

Seven hundred forty-nine women.

INTERVENTION(S)

Controlled ovarian stimulation with hphMG or rFSH in a GnRH antagonist cycle with compulsory single-blastocyst transfer on day 5 in one fresh or subsequent frozen blastocyst replacement in natural cycles initiated within 1 year of each patient's start of treatment.

MAIN OUTCOME MEASURE(S)

Ongoing pregnancy (primary end point) and live birth rates, as well as pharmacodynamic parameters.

RESULT(S)

The ongoing pregnancy rate after a fresh cycle was 30% with hphMG versus 27% with rFSH for the per-protocol (PP) population and 29% versus 27% for the intention-to-treat (ITT) population. Noninferiority of hphMG compared to rFSH was established. Considering frozen cycles initiated within 1 year, the cumulative live birth rate for a single stimulation cycle was 40% and 38% for women treated with hphMG and rFSH, respectively (both PP and ITT). Significant differences in pharmacodynamic end points were found between the two gonadotropin preparations.

CONCLUSION(S)

Highly purified hMG is at least as effective as rFSH in GnRH antagonist cycles with compulsory single-blastocyst transfer.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00884221.

In vitro development and gene expression of frozen-thawed 8-cell stage mouse embryos following slow freezing or vitrification

Objective

This study was performed to compare the efficiency of slow freezing and vitrification based on survival, development to blastocysts, and cell numbers of blastocysts. Changes in embryonic gene expression in fresh and frozen-thawed embryos were also examined.

Methods

Eight-cell stage embryos were collected from superovulated female BDF1 mice. The collected embryos were randomly divided into three groups. One group was maintained as fresh controls (n=42), one was frozen by slow freezing (n=43), and one was cooled by vitrification (n=43). After thawing or cooling, survival rates, development to blastocyst, and cell numbers and inner cell mass (ICM) cell numbers of blastocysts were compared with those of the control group. The expressions of eight genes (Rbm3, Birc5, Sod1, Sod2, Cirbp, Caspase3, Trp53, Hsp70.1) were examined by real time-quantitative polymerase chain reaction in the fresh and frozen-thawed embryos.

Results

There were no significant differences in the slow freezing and vitrification groups' survival rate after thawing (88.4% vs. 88.4%), development to blastocyst (100% vs. 97.4%), cell numbers (107.0±21.0 vs. 115.0±19.7), or ICM cell numbers of blastocysts (11.3±5.2 vs. 11.1±3.7). Cell numbers of blastocysts were significantly (p<0.05) lower in the frozen-thawed embryos than the fresh embryos. There were no significant differences in the slow freezing and the vitrification groups' expressions of the eight genes. The expressions of CirbP and Hsp70.1 were higher in the frozen-thawed embryos than in the fresh embryos but there were no significant differences.

Conclusion

These results suggest that there were no significant differences between embryos that underwent slow freezing and vitrification.

[Outcome of embryo vitrification compared to slow freezing process at early cleavage stages. Report of the first French birth]

OBJECTIVES

Since the end of 2010, France by "l'Agence de Biomédecine" has validated the embryo vitrification procedure as an improvement of the slow freezing method. We presented here data concerning biological and clinical outcomes from a prospective observational study where early cleavage stage good quality embryos were vitrified and warmed. We compared these results to those of a retrospective series where embryos were thawed after a slow freezing procedure (SF). We report also the first French live birth following embryo vitrification.

PATIENTS AND METHODS

In all, 58 cycles of frozen-thawed embryo transfers (FET) following vitrification were prospectively included and compared with 189 FET from SF method. Primary end points were the (i) survival rate (SR) (% of embryos with ≥50% post-thaw intact blastomeres), (ii) intact survival rate (ISR) (% of embryos with 100% post-thaw intact blastomeres) and (iii) survival blastomeres index (SBI) (% of post thaw intact blastomeres per survival embryo). Secondary end point was the clinical pregnancy rate (CPR) defined as the presence of an intra-uterine gestational sac with positive foetal heart beat. We report here the first French live birth following embryo vitrification.

RESULTS

In all, 87 and 412 embryos have been thawed following vitrification and SF, respectively. We observed a highly significant increase of SR, ISR et SBI respectively when thawing concerned vitrified embryos rather than those from SF method (98.3±13.1% vs. 77.3±32.0%, P<10(-4); 88.2±28.3% vs. 47.7±41.4%, P<10(-4); 97.7±6.1% vs. 87.3±14.4%, P<10(-4)). Furthermore, CPR were of 32.7% (19/58) and of 18.5% (35/189) following FET performed after vitrification or SF and thawing (P=0.03), respectively. The live birth of two healthy girls occurred following a caesarean section after 38 weeks of amenorrhea the 8th of August 2011.

DISCUSSION AND CONCLUSION

We experienced in our study that the post-thaw survival of vitrified embryos was significantly better than those of embryos resulting from SF. Then, a better CPR per thawed embryo cycle was observed following vitrification.

Comparing thaw survival, implantation and live birth rates from cryopreserved zygotes, embryos and blastocysts

CONTEXT:

Most in vitro fertilization (IVF) programs employ embryo cryopreservation to enhance pregnancies from a single ovarian stimulation. More embryos are created, some of which are not transferred to the uterus immediately, generating a need for improved cryopreservation protocols. One protocol may involve growing embryos to a further stage of development, allowing only embryos with proven developmental capabilities to be cryopreserved. Here we examined thaw survival, implantation and live birth rates of embryos cryopreserved at different stages.

AIMS:

We examined thaw survival, implantation and live birth rates of embryos cryopreserved at the zygote, day 3 (D3) embryos or blastocyst stage.

SETTINGS AND DESIGN:

This is a retrospective study from a single academic IVF program.

PATIENTS AND METHODS:

A retrospective study of all patients who had frozen embryos transferred to their uteri from year 2002 to 2008 at a single academic IVF program was conducted.

STATISTICAL ANALYSIS USED:

Analysis of variance followed by Fisher's Exact Test was performed to compare the survival after thaw, implantation and live birth rates between the three groups.

RESULTS:

One thousand nine hundred and ninety-one zygotes, 2880 D3 embryos and 503 blastocysts were frozen using a slow freeze technique, thawed and transferred. Significantly more D3 embryos and blastocysts survived the thawing process compared to zygotes and significantly higher implantation rate per number of thawed blastocysts was achieved than that for zygotes. Live birth rates were similar between the three groups.

CONCLUSIONS:

Growing embryos to blastocyst stage prior to cryopreservation is associated with fewer frozen embryos but does not appear compromise patients’ chance of achieving pregnancy

New algorithm for OHSS prevention

Ovarian hyperstimulation syndrome (OHSS) still remains a life-threatening complication of in vitro fertilization treatment (IVF), keeping patients and especially those, who previously experienced OHSS, from attempting infertility treatment and childbearing. The recent implementation of four new modalities: the GnRH antagonist protocol, GnRH agonist (GnRHa) triggering of ovulation, blastocyst transfer and embryo/oocyte vitrification, renders feasible the elimination of OHSS in connection with ovarian hyperstimulation for IVF treatment. The proposed current algorithm is based on the number of follicles developed after ovarian stimulation, setting a cut-off level at the development of 18 or more follicles. Further, fulfilling this criterion, the algorithm is based on four decision-making points: the final day of patient work-up, the day of triggering final oocyte maturation, day-1 post oocyte pick-up (OPU) and day-5 post OPU. If the physician decides to administer hCG for final oocyte maturation regardless the type of analogue used, he has the option on day-1 to either freeze all embryos or to proceed to day-5. On this day, based on the clinical condition of the patient, a decision should be made to either transfer a single blastocyst or to vitrify all blastocysts available. However, this strategy will not guarantee an OHSS free luteal phase especially if a pregnancy occurs. If the physician decides to trigger ovulation with GnRHa, feasible only with the antagonist protocol, embryos can be cultured until day-5. On this day a transfer can be performed with no risk of OHSS and spare blastocysts may be vitrified. Alternatively, on day-1 or day-2 post OPU, all embryos could be frozen. Hopefully, in a near future, GnRHa triggering and vitrification of oocytes will become everyday practice. Only the combined use of a GnRH antagonist protocol with GnRHa triggering and subsequent single blastocyst transfer or embryo/oocyte freezing will completely abolish the risk of OHSS after ovarian hyperstimulation.

Effects of cryopreservation on the meiotic spindle, cortical granule distribution and development of rabbit oocytes

Although much progress has been made in oocyte cryopreservation since 1971, live offspring have only been obtained in a few species and in rabbits. The aim of our study was to evaluate the effect of vitrification and slow freezing on the meiotic spindle, cortical granule (CG) distribution and their developmental competence. Oocytes were vitrified in 16.84% ethylene glycol, 12.86% formamide, 22.3% dimethyl sulphoxide, 7% PVP and 1% of synthetic ice blockers using Cryotop as device or slow freezing in 1.5 m PROH and 0.2 m sucrose in 0.25 ml sterile French mini straws. Meiotic spindle and CG distribution were assessed using a confocal laser-scanning microscope. To determine oocyte competence, in vitro development of oocytes from each cryopreservation procedure was assessed using parthenogenesis activation. Our data showed that oocytes were significantly affected by both cryopreservation procedures. In particular, meiotic spindle organization was dramatically altered after cryopreservation. Oocytes with peripheral CG distribution have a better chance of survival in cryopreservation after slow-freezing procedures compared to vitrification. In addition, slow freezing of oocytes led to higher cleavage and blastocyst rates compared to vitrification. Our data showed that, in rabbits, structural alterations are more evident in vitrified oocytes than in slow-frozen oocytes, probably as a consequence of sensitivity to high levels of cryoprotectants. Slow-freezing method is currently the recommended option for rabbit oocyte cryopreservation.

Should a single blastocyst transfer policy be a clinical decision or should it depend on the embryological evaluation on day 3?

BACKGROUND

Single blastocyst transfer has the advantage of maximizing the fresh single pregnancy rate. However, in patients with a low number of good quality embryos on day 3, it remains unclear whether immediate embryo transfer or further embryo culture with blastocyst transfer is the most preferable option.

METHODS

A retrospective cohort study was carried out in which the outcome of 590 fresh in vitro fertilization (IVF) cycles over a 15 months period and their cryo cycles were analyzed. A total of 341 patients cycles had an elective day 5 strategy independent of intermediate embryo evaluation while another 249 patients underwent a day 5 embryo transfer only if at least four embryos were available on day 3. Blastocyst vitrification was performed using a closed high security system.

RESULTS

Demographics, stimulation parameters and embryological data were comparable in the two groups. Patients in the elective day 5 group had a lower fresh transfer rate (90.62% vs. 95.18%, p < 0.05) as compared to patients with a day 3 or day 5 embryo transfer policy. No difference was observed in the fresh live birth rate and multiple pregnancy rate per initiated cycle (32.84% vs. 28.92%; 1.17% vs 0%) The projected cumulative ongoing pregnancy rate compensating for double counting in case subjects have more than one pregnancy is not different (42.58% vs. 39.84%).

CONCLUSIONS

Despite lower fresh transfer rates, elective single blastocyst transfer yields a similar projected cumulative ongoing pregnancy rate as in a policy with cleavage stage or blastocyst transfer depending on a good quality embryo count on day 3.

Vitrification of mouse embryos with super-cooled air

OBJECTIVE

To develop a closed vitrification device (i.e., one that requires no direct contact with liquid nitrogen) for successful cryostorage of embryos.

DESIGN

Prospective laboratory research study.

SETTING

University-based research laboratory.

ANIMAL(S)

F1 mice and mouse embryos.

INTERVENTION(S)

Mouse embryos were vitrified using two methods and compared with nonvitrified controls. Embryos were vitrified on a device by either [1] presealing it within a straw before plunging into liquid nitrogen or [2] placing the straw into liquid nitrogen so that the air inside the straw is super-cooled before inserting the device holding the embryos.

MAIN OUTCOME MEASURE(S)

Survival, subsequent embryo development, and cell number were determined. Embryos were also cryopreserved for 12 months to assess long-term storage. Synchronized ETs were performed to compare viability with nonvitrified control embryos.

RESULT(S)

All embryos survived with both techniques. Day-4 and -5 embryo development was comparable between the two vitrification methods. Use of the presealing method resulted in a significantly lower mean cell number than the postsealing method and control. Long-term storage did not affect subsequent embryo development or cell number. The implantation and fetal development rates of embryos vitrified with super-cooled air were comparable to those for nonvitrified control embryos.

CONCLUSION(S)

These data demonstrate that a closed vitrification device (Rapid-i), which does not require direct liquid nitrogen contact for vitrification, is appropriate for vitrification and long-term storage of mouse embryos.

Vitrification of mouse embryo-derived ICM cells: a tool for preserving embryonic stem cell potential?

Purpose

Vitrification technology presents new opportunities for preservation of embryo derived stem cells without first establishing a viable ESC line. This study tests the feasibility of cryopreserving ICM cells using vitrification.

Materials and Methods

ICMs from mouse embryos were isolated and vitrified in HSV straws or on cryoloops. Upon warming, the vitrified ICMs were cultured and observed for attachment and morphology. Colonies were passaged every 3–6 days. ICMs and ICM-derived ESC colonies were tested for expression of stem cell specific markers.

Results

ICMs vitrified on both the cryoloop and the HSV straw had high survival rates. ICM derived ESCs remained undifferentiated for several passages and demonstrated expression of typical stem cell markers; SSEA-1, Sox-2, Oct 4 and alkaline phosphatase.

Conclusion

This is the first report on successful vitrification of isolated ICMs and the subsequent derivation of ESC colonies. Vitrification of isolated ICMs is a novel approach for preservation of the “stem cell source” material.

Effect of cryotop vitrification on preimplantation developmental competence of murine morula and blastocyst stage embryos

Vitrification is an effective method for the cryopreservation of mammalian embryos. Nevertheless, it is unclear which embryonic developmental stage is the most suited for vitrification and would ensure maximal developmental competence upon subsequent warming. This study, therefore, compared the effects of cryotop vitrification on the developmental competence of murine morula and blastocyst stage embryos. Additionally, trophectoderm (TE) and inner cell mass (ICM) cell numbers were compared in two hatched blastocyst groups derived from vitrified morulae and blastocysts, respectively. The post-vitrification survival rates for mouse embryos at the morula and blastocyst stage were 95.4% (186/195) and 96.5% (195/202), respectively. The blastocyst formation rate was significantly lower for vitrified morulae (90.3%) compared with the non-vitrified control group (98.4%) (P < 0.05). The hatching rates were similar between the vitrified morula (79.6%) and the vitrified blastocyst (81.0%) groups. When further development to the fully hatched blastocyst stage was compared, fully hatched blastocysts derived from vitrified morulae had significantly higher cell counts for both the ICM and TE lineage, as compared with hatched blastocysts derived from vitrified blastocysts (P < 0.001). Cryotop vitrification of mouse embryos at the morula stage rather than blastocyst stage would thus ensure a higher degree of post-warming developmental competence.

Human cleavage-stage embryo vitrification is comparable to slow-rate cryopreservation in cycles of assisted reproduction

OBJECTIVES

To compare embryo survival, pregnancy and implantation rates after cryopreservation of human cleavage-stage embryos with slow-rate cryopreservation or vitrification.

STUDY DESIGN

262 patients, attending for assisted reproduction, were prepared for oocyte retrieval using standard controlled ovarian hyperstimulation protocols. Excess embryos were cryopreserved on day 3 either by vitrification, or slow-rate cryopreservation in a programmable freezer. Cycles of thawing were monitored for thaw efficiency, pregnancy and implantation rates.

RESULTS

Clinical pregnancy and implantation rates were highly comparable between cycles in which day 3 embryos were thawed either after slow-rate cryopreservation or vitrification.

CONCLUSIONS

These data suggest that vitrification of human embryos during assisted reproduction cycles achieves comparable success rates to fresh cycles and therefore can be applied in the laboratory of assisted reproduction.

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.

Prospective randomized comparison of human oocyte cryopreservation with slow-rate freezing or vitrification

OBJECTIVE

To compare cryopreservation of mature human oocytes with slow-rate freezing and vitrification and determine which is most efficient at establishing a pregnancy.

DESIGN

Prospective randomized.

SETTING

Academically affiliated, private fertility center.

PATIENT(S)

Consenting patients with concerns about embryo cryopreservation and more than nine mature oocytes at retrieval were randomized to slow-rate freezing or vitrification of supernumerary (more than nine) oocytes.

INTERVENTION(S)

Oocytes were frozen or vitrified, and upon request oocytes were thawed or warmed, respectively.

MAIN OUTCOME MEASURE(S)

Oocyte survival, fertilization, embryo development, and clinical pregnancy.

RESULT(S)

Patient use has resulted in 30 thaws and 48 warmings. Women's age at time of cryopreservation was similar. Oocyte survival was significantly higher following vitrification/warming (81%) compared with freezing/thawing (67%). Fertilization was more successful in oocytes vitrified/warmed compared with frozen/thawed. Fertilized oocytes from vitrification/warming had significantly better cleavage rates (84%) compared with freezing/thawing (71%) and resulted in embryos with significantly better morphology. Although similar numbers of embryos were transferred, embryos resulting from vitrified oocytes had significantly enhanced clinical (38%) pregnancy rates compared with embryos resulting from frozen oocyte (13%). Miscarriage and/or spontaneous abortion rates were similar.

CONCLUSION(S)

Our results suggest that vitrification/warming is currently the most efficient means of oocyte cryopreservation in relation to subsequent success in establishing pregnancy.

Clinical pregnancy and live births after transfer of embryos vitrified on day 3

Human embryo vitrification is a promising new technology but clinical outcome data is needed to gauge its effectiveness and safety. While pregnancy and live-birth data is available for blastocyst vitrification, such information is lacking for human embryo vitrification at the 6- to 8-cell stage. The current work presents clinical and obstetric outcomes from the transfer of embryos vitrified on day 3 at the cleavage stage. A total of 270 transfers were performed. The clinical pregnancy and implantation rates for patients under 38 years of age (n=200) were 45% and 24%, respectively. Corresponding rates in patients 38-42 years old declined to 29% and 13% (n=70). Embryonic compaction and/or blastulation by the time of transfer were excellent prognostic indicators of a successful pregnancy outcome. Of the 66 deliveries, 12 (18.2%) were twin pregnancies and nine were preterm (13.6%). The mean birthweight for singletons was 3281+/-644 g, compared with 2506+/-549 g in the twin pregnancies. A total of 78 infants have been born with no major congenital malformations. These data attest to the efficacy and safety of the vitrification technique for cryopreservation of human embryos at the 6- to 8-cell stage.

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.

Slow freezing, vitrification and ultra-rapid freezing of human embryos: a systematic review and meta-analysis

Embryo cryopreservation is an important aspect of assisted reproduction. Many methods have been described, but they have been poorly investigated in randomized trials, highlighting the need for a systematic review of the literature. Meticulous electronic/hand searches were performed to locate randomized trials (RCT) comparing embryo cryopreservation methods. Primary outcomes were clinical pregnancy rate (CPR) and incidence of congenital abnormalities. Secondary outcomes included live-birth (LBR), ongoing pregnancy (OPR), implantation (IR), and miscarriage (MR) rates. Data were extracted to allow for an intention-to-treat analysis and analysed using a random-effects model. Literature search revealed 11 RCT, of which five were excluded. The quality of the included studies was variable, but generally poor. There was a significantly higher CPR, OPR and IR with vitrification compared with slow freezing (odds ratio (OR)=1.55, 95% confidence interval (CI)=1.03-2.32, OR=1.82, 95% CI=1.04-3.20 and OR=1.49, 95% CI=1.03-2.15, respectively). In addition, there was a significantly lower CPR and OPR with embryo ultra-rapid freezing compared with slow freezing (OR=0.35, 95% CI=0.16-0.76 and OR=0.37, 95% CI=0.17-0.81, respectively). Vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing. However, more well-designed and powered studies are needed to further corroborate these findings.

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.

Follicle survival and growth to antral stages in short-term murine ovarian cortical transplants after Cryologic solid surface vitrification or slow-rate freezing

This study was designed to asses murine preantral follicle survival and growth, after cryopreservation of ovarian tissue by two different methodologies, solid-surface vitrification by the Cryologic vitrification method (CVM) and slow-rate freezing (SRF). Cryotreated tissue was stored in liquid nitrogen for 24h, and upon warming follicle viability was assessed by live/dead fluorescent probes, and by 7-day autotransplantation of both cryotreated tissue types to the left and right kidney capsule of the donor animals (n=16). The live/dead assay immediately upon tissue warming did not allow a distinction to be made in terms of follicle viability between the CVM and SRF cryoprocedure. In grafted tissue, follicular survival and growth was assessed by conventional histological examination and proliferating cell nuclear antigen immunohistochemistry. In each experimental group (control, CVM and SRF), follicles were classified according to developmental stage, and a comparison of the proportions of follicle stages between the three groups was executed by statistical analysis of variance. The fraction of primordial follicles in CVM and SRF grafts significantly decreased as compared to control tissue, whereas intermediary and primary follicles significantly increased. The proportion of secondary and antral follicles after SRF was significantly larger than after CVM, but did not differ significantly between CVM and control tissue. The observed massive follicle activation is a typical transplantation effect, but testifies to the survival of cryopreserved follicles. In both types of cryotreated tissue, growing follicles, including antral stage, were present in grafts from all recipient animals. The significantly more abundant further developed stages in SRF treated tissue, however, suggest that CVM treated tissue may have suffered a growth disadvantage. To our knowledge, this is the first time that the CVM technique has been utilized to vitrify preantral follicles.