An overview of oocyte cryopreservation

A PolScope evaluation of meiotic spindle dynamics in frozen-thawed oocytes

In mature human oocytes, the metaphase II (MII) spindle presence and birefringence signal detected through the PolScope may vary before and after freezing. In particular, spindle dynamics during the first few hours after thawing is still under study. In this study, oocytes from stimulated ovaries were cryopreserved in 1.5 mol/l 1,2-propanediol with 0.3 mol/l sucrose using a slow freezing-rapid thawing method. Oocytes were examined with the PolScope for the presence, intensity of signal birefringence and size of the meiotic spindle before freezing and at 0, 1 and 2 h post-thaw (where 0 h = the time of the end of the thawing procedure). Of the 173 surviving oocytes exhibiting a spindle before freezing, 82.7% (143/173) showed spindle birefringence within 1 h of thawing. However, at the end of the thawing procedure the intensity of spindle birefringence (retardance) and the spindle length were smaller in comparison to the pre-freezing condition. These parameters increased after 1 h, although were not restored to the value observed before freezing. No significant changes were observed by extending the culture to 2 h.

Vitrification of cleavage stage mouse embryos by the cryoloop procedure

By decreasing the volume of the cryoprotective solution it is possible to increase dramatically the freezing speed and - at the same time - reduce the toxicity and osmotic side effects of cryoprotectants (CPA). The objective of our study was to vitrify Day-3 cleavage stage mouse embryos (n = 229) with the cryoloop technology using a new composition of vitrification media. Embryos were exposed to a 2-step loading of CPA, ethylene glycol (EG) and propylene glycol (PG), before being placed on the surface of a thin filmy layer formed from the vitrification solution in a small nylon loop, then they were rapidly submerged into liquid nitrogen. After warming, the CPA was diluted out from the embryos by a 3-step procedure. Survival of embryos was based on morphological appearance after thawing and continued development to expanded blastocysts upon subsequent 48-hour culture. Embryos of the two control groups were either treated likewise except that they were not vitrified, or cultured in vitro without any treatment. Our data show that a high percentage of embryos survived (92.7%) vitrification in the mixture of EG and PG combined with cryoloop carrier and developed normally (89.1%) in vitro after thawing. To our knowledge this is the first report of the successful vitrification of cleavage stage mouse embryos using VitroLoop vitrification procedure.

Addressing fertility needs of breast cancer patients: oncology perspective

Premenopausal women represent approximately 23% of women diagnosed with breast cancer. As the medial age of first pregnancy increases in developed countries, a greater proportion of women are diagnosed with breast cancer at a time when they have not yet completed their family. For these women, the impact of breast cancer treatment on their reproductive capacity can be of significant concern and may influence their treatment decisions. Despite these concerns only a proportion of premenopausal women with breast cancer are informed about their treatment choices in light of their reproductive needs. The diagnosis of cancer itself as well as systemic cancer treatments, including chemotherapy and hormonal therapy, can delay and/or reduce the reproductive capacity. Treatment decisions need to consider not only adjuvant treatment efficacy but also its risks, including impact on fertility. The risk of chemotherapy-associated amenorrhea varies according to the regime and is age-dependent. Hormonal treatments may delay reproduction further. A variety of fertility preservation strategies have been tried including gonadal protection during chemotherapy, ovarian cryopreservation and in vitro fertilization, but their potential benefits need to be considered in light of risks and, for most of them, the evidence for efficacy is limited. Special fertility considerations are required in women with family history and/or evidence of genetic predisposition to breast cancer as strategies for risk reduction may impact on their fertility choices. Finally, as survival of women with metastatic breast cancer increases, women with advanced cancer who become pregnant pose unique management challenges for oncologists and obstetricians alike.

Obstetric and perinatal outcome in 200 infants conceived from vitrified oocytes

Cryopreservation of oocytes by vitrification is a promising new technique for assisted human reproduction. Any new technical development must be accompanied with data concerning obstetric and perinatal outcome. This study analysed the obstetric and perinatal outcomes in 165 pregnancies and 200 infants conceived following oocyte vitrification cycles in three assisted reproduction centres. The results indicate that the mean birth weight and the incidence of congenital anomalies are comparable to that of spontaneous conceptions in fertile women or infertile women undergoing in-vitro fertilization treatment. These preliminary findings may provide reassuring evidence that pregnancies and infants conceived following oocyte vitrification are not associated with increased risk of adverse obstetric and perinatal outcomes.

Oocyte cryopreservation: the birth of the first Hungarian babies from frozen oocytes

PURPOSE

To present data obtained with clinical application of oocyte cryopreservation.

METHODS

Slow freezing/rapid thawing in PBS based medium containing 1.5 M propanediol + 0.3 M sucrose.

RESULTS

A total of 127 embryos were transferred into 54 patients (1.9 embryo/cycle, 64 transfer cycles). Clinical pregnancy rate of 20% per cycle (13/64) and 24.0% per patient were achieved. Up-to-date, six patients delivered seven healthy babies; there are four ongoing pregnancies. Three abortions (23%) and one biochemical pregnancy (0.7%) was obtained. Implantation rates of 11% per transferred embryos (14/127) and 6.5% (14/215) per thawed eggs were found. In each case, normal karyotype was detected. No difference was found in the ratio of spindle positive oocytes at the polscope analyses done before and after freezing (75.8% vs. 82.5%).

CONCLUSION

Egg freezing is not a routine procedure yet, but there will certainly be a place for it in the future of assisted reproductive medicine.

Human oocyte and ovarian tissue cryopreservation and its application

PURPOSE

To review the recent progress in human oocyte and ovarian tissue cryopreservation, and in the application of these two technologies for preserving female fertility of patients who are undergoing cancer treatment.

DESIGN

The literature on human oocyte and ovarian tissue freezing was searched with PubMed. The scientific background, current developments and potential future applications of these two methods were reviewed.

RESULTS

Chemotherapy and/or radiotherapy can induce premature ovarian failure in most of female cancer patients. Consequently, there has been a greater need for options to preserve the reproductive potential of these individuals. However, options are somewhat limited currently, particularly following aggressive chemotherapy and/or radiotherapy treatment protocols. In recent years, there have been considerable advances in the cryopreservation of human oocytes and ovarian tissue. For women facing upcoming cancer therapies, cryopreservation of ovarian tissue and oocytes is a technology that holds promise for banking reproductive potential for the future. Recent laboratory modifications have resulted in improved oocyte survival, oocyte fertilization, and pregnancy rates from frozen-thawed oocytes in IVF. This suggests potential for clinical application.

CONCLUSIONS

In the case of patients who are facing infertility due to cancer therapy, oocyte cryopreservation may be one of the few options available. Ovarian tissue cryopreservation can only be recommended as an experimental protocol in carefully selected patients. In ovarian tissue transplantation, more research is needed in order to enhance the revascularization process with the goal of reducing the follicular loss that takes place after tissue grafting. These technologies are still investigational, although tremendous progress has been made. The availability of such treatment will potentially lead to its demand not only from patients with cancer but also from healthy women who chose to postpone childbearing until later in life and therefore wish to retain their fertility.

Fertility preservation for women with malignancies: current developments of cryopreservation

The preservation of fertility in female cancer survivors has become an important health issue. The different cryopreservation options available for fertility preservation are embryo, oocyte, and ovarian tissue cryopreservation. Oocyte cryopreservation is available for women without partners, but there is a limited experience with this technique and the pregnancy rate is still low. In spite of recent reports of successful birth after autotransplantation of cryopreserved-thawed human ovarian cortical tissues, clinical experience is also limited and this technique remains still experimental. Whole ovary cryopreservation itself poses several challenges. Further researches for establishing optimal cryopreservation and thawing protocols and increasing post-thawing survival, pregnancy, and delivery rates are necessary. In this article, the strategies for fertility preservation in cancer survivors are discussed. The different options and their results are discussed, as well as their indications, efficacy and ethical issues.

Human oocyte vitrification: the permeability of metaphase II oocytes to water and ethylene glycol and the appliance toward vitrification

OBJECTIVE

To determine the permeability of human metaphase II oocytes to ethylene glycol and water in the presence of ethylene glycol, and to use this information to develop a method to vitrify human oocytes.

DESIGN

An incomplete randomized block design.

SETTING

A university-affiliated assisted reproductive center.

PATIENT(S)

Women undergoing assisted reproduction in the Center for Reproductive Medicine at Shandong University.

INTERVENTION(S)

Oocytes were exposed to 1.0 molar ethylene glycol in a single step and photographed during subsequent volume excursions.

MAIN OUTCOME MEASURE(S)

A two-parameter model was employed to estimate the permeability to water and ethylene glycol.

RESULT(S)

Water permeability ranged from 0.15 to 1.17 microm/(min.atm), and ethylene glycol permeability ranged from 1.5 to 30 microm/min between 7 degrees C at 36 degrees C. The activation energies for water and ethylene glycol permeability were 14.42 Kcal/mol and 21.20 Kcal/mol, respectively.

CONCLUSION(S)

Despite the lower permeability of human metaphase II oocytes to ethylene glycol compared with previously published values for propylene glycol and dimethylsulfoxide, methods to add and remove human oocytes with a vitrifiable concentration of ethylene glycol can be designed that prevent excessive osmotic stress and minimize exposure to high concentrations of this compound.

Desiccation kinetics and biothermodynamics of glass forming trehalose solutions in thin films

In this study, the desiccation kinetics of aqueous trehalose solutions were investigated numerically by solving the coupled heat and mass transfer problem with a moving interface using the finite element method. The free volume models for vapor pressure and mutual diffusion coefficient were incorporated into the model to account for the effect of glass transition on the heat and mass transport process that ultimately determines the desiccation kinetics. It was found that the temperature in the film could drop significantly upon the initiation of drying due to the absorption of latent heat associated with water evaporation although the spatial distribution of temperature in the solution is very homogeneous. On the contrary, the spatial distribution of water content in the solution is non-homogeneous, particularly at the solution-vapor interface where an extremely thin layer of skin with extremely low molecular mobility usually forms during drying. The solution film can be dried to approximately 6-10 wt.% residual water within minutes for thin films; but drying times depends strongly on the initial film thickness, initial solution concentration, temperature, and convective coefficient. Desiccation to below 6 wt.% residual water is very slow due to the retarded water mobility in the extremely thin skin where the solution is in the glassy state. Since the water mobility in a trehalose solution or glass with 6-10% residual water is still high enough to allow degradative reactions to occur in a relatively short time at room temperature, it is important that the samples should be kept at a temperature around 0 degrees C or lower for storage after drying. Furthermore, approaches that might enable further quick reduction of the residual water to less than 6-10 wt.% are also proposed so that a sample could be preserved at super-zero or even room temperature. The established models and the reported results will be useful for the development of effective protocols for lyopreservation of biomaterials including living cells using trehalose as the excipient.

Cell encapsulating droplet vitrification

The capability to encapsulate single cells in droplets while retaining high cell viability (>90%) has great impact on tissue engineering, high-throughput screening, as well as clinical diagnostics and therapeutics. We demonstrate a novel method to vitrify a small number of cells using cell-encapsulating droplets. The method allows vitrification at low cryoprotectant concentration (1.5 M propanediol and 0.5 M trehalose), similar to that used in slow freezing protocols. The method was successfully applied to five different mammalian cell types: AML-12 hepatocytes, NIH-3T3 fibroblasts, HL-1 cardiomyocytes, mouse embryonic stem cells, and RAJI cells.

A review on reproductive biotechnologies for conservation of endangered mammalian species

This review describes the use of modern reproductive biotechnologies or assisted reproductive techniques (ART) including artificial insemination, embryo transfer/sexing, in vitro fertilization, gamete/embryo micromanipulation, semen sexing, genome resource banking, and somatic cell nuclear transfer (cloning) in conservation programs for endangered mammalian species. Such biotechnologies allow more offspring to be obtained from selected parents to ensure genetic diversity and may reduce the interval between generations. However, the application of reproductive biotechnologies for endangered free-living mammals is rarer than for endangered domestic breeds. Progress in ART for non-domestic species will continue at a slow pace due to limited resources, but also because the management and conservation of endangered species is biologically quite complex. In practice, current reproductive biotechnologies are species-specific or inefficient for many endangered animals because of insufficient knowledge on basic reproduction like estrous cycle, seasonality, structural anatomy, gamete physiology and site for semen deposition or embryo transfer of non-domestic species.

Reconstruction of ooplasm recipient oocytes with frozen-thawed donor microcytoplasts and influence on the microtubular spindle

OBJECTIVE(S)

To cryopreserve micromanipulated ooplast segments (microcytoplasts) from mouse oocytes, compare microcytoplast and parent or recipient oocyte fusion performed within or without the zona pellucida, compare electrofusion of fresh or frozen oocyte with frozen-thawed microcytoplasts, and assess spindle integrity after reconstruction of oocytes.

DESIGN

Prospective experimental study.

SETTING

University-based experimental laboratory.

ANIMAL(S)

Mouse (MII) oocytes obtained after superovulation (n = 363).

INTERVENTION(S)

Micromanipulation of oocytes (n = 363) into microcytoplasts (n = 181), cryopreservation of microcytoplasts along with parent and sibling control oocytes (n = 182), reconstruction by electrofusion of microcytoplast and parent or recipient oocyte performed with (group A, n = 35) or without a zona pellucida (group B, n = 32), comparison of electrofusion of fresh oocyte (group C, n = 40) or frozen oocyte (group D, n = 36) with frozen-thawed microcytoplasts fused within zona, and assessment of spindle morphology of reconstructed oocyte.

MAIN OUTCOME MEASURE(S)

Post-thaw survival, success of fusion, and spindle integrity as assessed by immunostaining.

RESULT(S)

Higher success of post-thaw fusion was seen in group A (91.4%) compared with group B (56.2%). The post-thaw fusion of microcytoplasts with either fresh or frozen oocytes was not significantly different. Spindle integrity was 82.5% in group C as compared with 47.2% in group D.

CONCLUSION(S)

Microcytoplasts created from oocytes can be successfully cryopreserved, thawed, and used to reconstruct oocytes with intact spindles.

Apoptosis and ultrastructural assessment after cryopreservation of whole human ovaries with their vascular pedicle

OBJECTIVE

To investigate possible damage caused by freeze-thawing whole human ovaries.

DESIGN

Prospective experimental study.

SETTING

Academic gynecology research unit in a university hospital.

PATIENT(S)

Ovaries were obtained from three women (aged 29-36 years).

INTERVENTION(S)

Ovaries were perfused and bathed in cryoprotective solution, and slow freezing was performed. Rapid thawing was achieved by perfusion and bathing with a decreased sucrose gradient.

MAIN OUTCOME MEASURE(S)

Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphates nick end-labeling (TUNEL) method and by immunohistochemistry for active caspase-3 in fresh ovaries, after cryoprotectant exposure, and after thawing. Morphometric analysis of TUNEL-positive surface area was performed. Ultrastructure was assessed by transmission electron microscopy (TEM) in the thawed tissue.

RESULT(S)

No primordial or primary follicles were found to be positive for either TUNEL or active caspase-3. No statistically significant difference in mean TUNEL-positive surface area values was found between the three groups: fresh, 0.05% +/- 0.03%, with 134 high-power fields (HPFs); cryoperfused, 0.02% +/- 0.01%, with 130 HPFs; and thawed, 0.09% +/- 0.03%, with 622 HPFs. By means of TEM, follicles and vessels showed a well-preserved ultrastructure, with 96.7% (29/30) healthy-looking primordial and primary follicles, and 96.3% (180/187) healthy-looking endothelial cells.

CONCLUSION(S)

Cryopreservation of intact human ovary with its vascular pedicle, according to the freeze-thawing protocol described here, is not associated with any signs of apoptosis or ultrastructural alterations in any cell types. Whole-organ vascular transplantation may thus be a viable option in the future.

Cryopreservation of mammalian oocytes

Two methods for the cryopreservation of mammalian oocytes are described. One method uses a relatively low concentration of the cryoprotectant propanediol plus sucrose and requires controlled-rate cooling equipment to achieve a slow cooling rate. Such a method has produced live births from cryopreserved human oocytes. The second method described employs a high concentration of the cryoprotectant dimethyl sulfoxide plus a low concentration of polyethylene glycol. This method involves cooling by plunging standard straws into liquid nitrogen vapor, hence avoiding the need for specialized equipment, but requires technical ability to manipulate the oocytes quickly in the highly concentrated cryoprotectant solutions. Murine oocytes vitrified, using this technique, have resulted in live births.

Survival rate of preantral follicles derived from vitrified neonate mouse ovarian tissue by Cryotop and conventional methods

The aim of this study was to investigate the growth and survival rate of preantral follicles isolated from vitrified ovarian tissue by Cryotop and conventional methods. The ovaries of 14-day-old mice were separated and divided into four groups as following: Cryotop group, vitrified by Cryotop; CV (Conventional; CV) group, vitrified by conventional straw; toxicity test group and control group. After warming the vitrified ovaries, isolated preantral follicles from four groups were cultured for 4 days to compare survival rate and follicular growth between above-mentioned groups. Survival rate (97.3%) in toxicity test group alike the control group (98.7%) were significantly higher (P<0.05) than the Cryotop (92.7%) and CV (47.7%) groups. Increase in follicle diameters after 4 days in Cryotop and CV groups was significantly lower (P<0.05) than the control and toxicity test groups, but growth and survival rate of follicles in Cryotop group was significantly higher (P<0.05) than the CV group. These results demonstrated that ovarian tissue vitrification by Cryotop highly preserves the viability rate of preantral follicles.

Oocyte cryopreservation: clinical outcome of slow-cooling protocols differing in sucrose concentration

Oocyte cryopreservation represents an important option for management of female fertility, avoiding the ethical concerns associated with embryo storage. This retrospective study evaluated the clinical outcome of two alternative slow freezing protocols involving different sucrose concentrations. From January 2004 to March 2006, spare oocytes from selected couples undergoing IVF or intracytoplasmic sperm injection were frozen using a slow-cooling protocol and thawed at a later stage. Patients were divided into two groups: group A (n = 65), whose oocytes were frozen with propane-1,2-diol (PrOH) and 0.1 mol/l sucrose; and group B (n = 66) whose oocytes were frozen with 0.3 mol/l sucrose. A total of 543 oocytes were thawed in group A and 601 in group B, achieving a survival rate of 24.3 and 71.2% respectively. Whilst fertilization rate (53.5 and 80.4% respectively) was higher in group B, enhanced results for group A were achieved over all (implantation rate per transferred embryos 12.2 versus 5.7%; pregnancy rate per transfer 16.7 versus 9.5%). Normal births and ongoing pregnancies have occurred in both groups. Although in slow-cooling methods higher sucrose concentration in the freezing mixture allows higher post-thaw survival and fertilization rates, overall this did not coincide with an improved clinical outcome.

Does oocyte cryopreservation have a future in Hungary?

The Committee of Human Reproduction established by the Hungarian Ministry of Health is currently working on a proposition that has the intention to ban oocyte cryopreservation in Hungary temporarily. According to the notion of the committee, oocyte cryopreservation and the utilization of frozen oocytes entail enormous risks for future generations. They argue that the safety of the method is unproven. Consequently, their standpoint maintains that cryopreservation invariably remains a grave risk factor with regards to the genetic material of the oocyte by significantly increasing the risk to the offspring. Therefore,the Committee is requesting additional animal experiments to clarify the probability of permanent lesions to the spindle and alterations to the genetic material. According to their point of view, the suspension of the method is further justified since the efficiency of the procedure has yet not reached the level required for clinical adaptation. With the proposed forthcoming step,this commentary takes the opportunity to make critical comments and clarify necessary questions.

Ultrastructure of human mature oocytes after slow cooling cryopreservation using different sucrose concentrations†

BACKGROUND

We studied the ultrastructural characteristics of human mature oocytes frozen/thawed (F/T) using different concentrations of sucrose. Fresh human mature oocytes were used as controls.

METHODS

The oocytes (n = 48) were fixed in 1.5% glutaraldehyde at sampling (n = 16) or after freeze/thawing performed using a slow cooling method with propane-1,2-diol 1.5 mol/l and sucrose at either 0.1 mol/l (n = 16) or 0.3 mol/l (n = 16) in the freezing solution. The oocytes were then processed for electron microscopy observations.

RESULTS

Fresh and F/T oocytes belonging to both study groups were regularly rounded in sections, with a homogeneous cytoplasm and an intact zona pellucida (ZP). Organelles (mainly mitochondria-smooth endoplasmic reticulum aggregates and mitochondria-vesicle complexes) were abundant and uniformly dispersed in the ooplasm. The amount and density of cortical granules appeared to be abnormally reduced in some F/T samples, independently of the sucrose concentration in the freezing solution: this feature was frequently associated with an increased density of the inner ZP, possibly related to the occurrence of zona 'hardening'. Furthermore, slight to moderate microvacuolization was revealed in the ooplasm of some F/T oocytes, particularly in those treated with sucrose 0.3 mol/l.

CONCLUSIONS

Freeze/thawing procedures are associated with ultrastructural alterations in specific oocyte microdomains, presumably linked to the reduced developmental potential of mature cryopreserved oocytes. Further work is needed to determine whether or not a high concentration of sucrose plays a role, at least in part, in producing the above alterations.

Measurement of essential physical properties of vitrification solutions

Vitrification is an "ice-free" cryopreservation method that has rapidly developed in recent years and might become the method of choice for oocyte cryopreservation. Five sources of damage should be considered when attempting to achieve successful oocyte cryopreservation by vitrification: (1) Solution effects (2) Crystallization (3) Glass fractures (4) Devitrification and recrystallization (5) Chilling injury. The probability of successful vitrification depends on three major factors: viscosity of the sample; cooling and warming rates; and sample volume. One of the problems associated with the vitrification solution is that it may contain high concentrations of cryoprotectants (CP), which can damage the cells through chemical toxicity and osmotic shock. In the present study, we examined the principal parameters associated with successful vitrification, and attempted to compose guidelines to the most important aspects of the vitrification process. The first step was the selection of a suitable and least toxic vitrification solution. We then evaluated the effects of cooling rate and volume on the probability of vitrification. Reduction of the sample volume, combined with accelerated cooling, enabled reduction of the CP concentration. However, in practice, a delicate balance must be maintained among all the factors that affect the probability of vitrification in order to prevent crystallization, devitrification, recrystallization, glass fractures and chilling injury.

Human oocyte cryopreservation: 5-year experience with a sodium-depleted slow freezing method

A slow freezing/rapid thawing method for the cryopreservation of human oocytes has been employed using a sodium-depleted culture media. In 53 frozen egg-embryo transfer (FEET) cycles, a 60.4% survival rate post-thaw was obtained and a 62.0% fertilization rate following intracytoplasmic sperm injection. Overall pregnancy rates were 26.4% per thaw attempt, 30.4% per patient, and 32.6% per embryo transfer. Pregnancy rates using sodium-depleted phosphate-buffered saline (PBS) as the base medium were 20.0% per thaw, 21.7% per patient, and 26.3% per transfer. With sodium-depleted modified human tubal fluid (mHTF) as the base for the cryopreservation medium, rates were 32.1% per thaw attempt, 39.1% per patient, 37.5% per transfer. The overall implantation rates were 4.2% per thawed oocyte and 13.6% per embryo, (PBS: 3.0% per egg, 10.6% per embryo; mHTF:5.3% per oocyte; 15.9% per embryo). These data indicate that the use of a sodium-depleted media with slow freezing and rapid thawing can yield acceptable pregnancy rates after FEET.

Comparison of in-vitro outcomes from cryopreserved oocytes and sibling fresh oocytes

In Italy, the restrictive IVF law generalizes the indication for oocyte freezing for surplus oocytes in 78.5% of in-vitro assisted reproductive cycles. With a view to understanding better what the prospects for intracytoplasmic sperm injection (ICSI) on frozen-thawed oocytes might be, the consequences of freeze-thaw procedures on fertilization, cleavage rates and embryo quality obtained from frozen-thawed oocytes were studied and compared with the results obtained from sibling fresh oocytes. Eleven IVF and 29 ICSI on 76 and 169 fresh oocytes were performed and the corresponding 40 ICSI on 221 sibling frozen-thawed oocytes. There was no difference in terms of fertilization rate between fresh and sibling frozen-thawed oocytes. The cleavage rate (98.0 and 94.4% with fresh oocytes in IVF and ICSI; 77.3% with frozen-thawed oocytes in ICSI; P < 0.001) and embryo quality (grade I embryos over total embryos: 36.7 and 22.2% with fresh oocytes in IVF and ICSI; 12.1% with frozen-thawed oocytes in ICSI; respectively P < 0.001 and P < 0.05) were statistically lower after oocyte cryopreservation. The significant decrease in meiotic spindle retrieval rate before freezing (62.4%) and after thawing procedures (43.4%; P < 0.001) suggests that cryoconservation induces irreversible damage to microtubule repolymerization. The consequences of oocyte cryopreservation procedures on embryo development are reviewed.

Delayed motherhood through oocyte and ovarian tissue cryopreservation - a perspective from Singapore

Recent advances in oocyte and ovarian tissue cryopreservation technology have brought hope not only to women facing premature loss of ovarian function, but also to healthy women seeking delayed motherhood. This is a major issue of contention in healthcare ethics. Proponents of this new technology argue that this enables women to pursue educational and career goals in their youth, so that they have greater financial security for children in later life. Nevertheless, this argument may be flawed by the reality that even if the cryopreservation of oocytes and ovarian tissue were optimized in the future, this would in no way be a guaranteed route for women to have biological children later in life. Moreover, because only a limited amount of autologous reproductive material can be cryopreserved and stored for a single healthy woman, there is a risk of material depletion before reproductive success is attained. Another prime consideration is the increased morbidity and mortality associated with clinical assisted reproduction in older women. Hence, it is imperative that delayed motherhood through the cryopreservation of oocytes and ovarian tissues be viewed with extreme caution, and mandatory counselling should be given to all patients if such a medical procedure ultimately finds approval for widespread application.

Vitrification of goat preantral follicles enclosed in ovarian tissue by using conventional and solid-surface vitrification methods

Caprine preantral follicles within ovarian fragments were exposed to or vitrified in the presence of sucrose, dimethyl sulfoxide (DMSO), ethylene glycol (EG), or various combinations thereof. The fragments were cryopreserved by using either a conventional (CV) or a solid-surface vitrification (SSV) protocol, and the cryoprotectants were removed by equilibrating vitrified ovarian fragments in "warming solution" consisting of minimum essential medium and heat-inactivated fetal calf serum (MEM(+)) followed by washes in MEM(+) with or without sucrose. Histological analysis of follicle integrity showed that the percentages of normal follicles in ovarian fragments vitrified in sucrose mixed with EG and/or DMSO (CV method) or mixed with EG or DMSO (SSV method) followed by washes in MEM(+) plus sucrose were similar to those of controls (ovarian fragments fixed without previous vitrification). Unlike for MEM(+) (supplemented or unsupplemented by sucrose) and DMSO followed by washes in the absence of sucrose, the percentages of normal follicles found after exposure to cryoprotectant did not significantly differ from that found after vitrification, indicating that follicular degeneration was attributable to a toxic effect of cryoprotectants and not to the vitrification procedure. The viability of preantral follicles after the CV and SSV procedures was investigated by using calcein-AM and the ethidium-homodimer as "live" and "dead" markers, respectively. In both tested vitrification procedures, the highest percentages of viable follicles were observed when a mixture of sucrose and EG (70.3% for CV and 72.4% for SSV) was used. Preantral follicles were also vitrified (either by CV or SSV) in sucrose and EG and then cultured for 24 h, after which their viability was compared with that of cultured fresh and uncultured vitrified follicles. The viability of these follicles was maintained after SSV, but not after CV. Thus, the viability of caprine preantral follicles can be best preserved after SSV in a mixture of sucrose and EG, followed by washes in medium containing sucrose.

Ovarian tissue cryopreservation and transplantation: a review

The review covers current options for ovarian tissue cryopreservation and transplantation and provides a systematic review of the existing literature from the last 10 years, taking into account all previously published reviews on the subject. The different cryopreservation options available for fertility preservation in cancer patients are embryo cryopreservation, oocyte cryopreservation and ovarian tissue cryopreservation. The choice depends on various parameters: the type and timing of chemotherapy, the type of cancer, the patient's age and the partner status. The different options and their results are discussed, as well as their putative indications and efficacy. The review concludes that advances in reproductive technology have made fertility preservation techniques a real possibility for patients whose gonadal function is threatened by premature menopause, or by treatments such as radiotherapy, chemotherapy or surgical castration.

Calcium-free vitrification reduces cryoprotectant-induced zona pellucida hardening and increases fertilization rates in mouse oocytes

Despite the success of embryo cyropreservation, routine oocyte freezing has proved elusive with only around 200 children born since the first reported birth in 1986. The reason for the poor efficiency is unclear, but evidence of zona pellucida hardening following oocyte freezing indicates that current protocols affect oocyte physiology. Here we report that two cryoprotectants commonly used in vitrification procedures, dimethyl sulfoxide (DMSO) and ethylene glycol, cause a large transient increase in intracellular calcium concentration in mouse metaphase II (MII) oocytes comparable to the initial increase triggered at fertilization. Removal of extracellular calcium from the medium failed to affect the response exacted by DMSO challenge, but significantly reduced the ethylene glycol-induced calcium increase. These results suggest that the source of the DMSO-induced calcium increase is solely from the internal calcium pool, as opposed to ethylene glycol that causes an influx of calcium across the plasma membrane from the external medium. By carrying out vitrification in calcium-free media, it was found that zona hardening is significantly reduced and subsequent fertilization and development to the two-cell stage significantly increased. Furthermore, such calcium-free treatment appears not to affect the embryo adversely, as shown by development rates to the blastocyst stage and cell number/allocation. Since zona hardening is one of the early activation events normally triggered by the sperm-induced calcium increases observed at fertilization, it is possible that other processes are negatively affected by the calcium rise caused by cryoprotectants used during oocyte freezing, which might explain the current poor efficiency of this technique.

Cumulative pregnancy rates resulting from the use of fresh and frozen oocytes: 7 years' experience

Storing supernumerary embryos and transferring them later fully utilizes the reproductive potential of retrieved oocytes, allowing a significant increase in the overall number of pregnancies achieved from a single cycle of ovarian stimulation treatment. As an alternative to embryo cryopreservation, preservation of unfertilized oocytes has been proposed to maximize clinical outcome. This paper presents data concerning the cumulative pregnancy rate after use of fresh and cryopreserved oocytes. In 80 treatment cycles in which patients chose to have only a few fresh oocytes inseminated, 24 pregnancies were obtained (30.0%), with an implantation rate of 22.6%. After cryopreservation with the standard slow-cooling protocol, the survival, fertilization and cleavage rates of 918 frozen oocytes were 43.4, 51.5 and 86.0% respectively. A total of 14 frozen pregnancies were achieved, with pregnancy rate 19.2% per transfer and implantation rate 12.3%. The cumulative pregnancy rate was 47.5% per patient. Therefore, despite a low rate of oocyte post-thaw survival, it appears that oocyte storage appreciably improves the number of pregnancies per treatment cycle in cases in which only a minority of oocytes are destined for the fresh treatment. This outcome provides valuable information for appraising the chances of clinical success when the option of embryo cryopreservation is not available.

Applications of emerging technologies to the study and conservation of threatened and endangered species

Sustaining viable populations of all wildlife species requires the maintenance of habitat, as well as an understanding of the behaviour and physiology of individual species. Despite substantial efforts, there are thousands of species threatened by extinction, often because of complex factors related to politics, social and environmental conditions and economic needs. When species become critically endangered, ex situ recovery programmes that include reproductive scientists are the usual first line of defence. Despite the potential of reproductive technologies for rapidly increasing numbers in such small populations, there are few examples of success. This is not the result of a failure on the part of the technologies per se, but rather is due to a lack of knowledge about the fundamental biology of the species in question, information essential for allowing reproductive technologies to be effective in the production of offspring. In addition, modern conservation concepts correctly emphasise the importance of maintaining heterozygosity to sustain genetic vigour, thereby limiting the practical usefulness of some procedures (such as nuclear transfer). However, because of the goal of maintaining all extant gene diversity and because, inevitably, many species are (or will become) 'critically endangered', it is necessary to explore every avenue for a potential contributory role. There are many 'emerging technologies' emanating from the study of livestock and laboratory animals. We predict that a subset of these may have application to the rescue of valuable genes from individual endangered species and eventually to the genetic management of entire populations or species. The present paper reviews the potential candidate techniques and their potential value (and limitations) to the study and conservation of rare wildlife species.

Advances in oocyte cryopreservation technology will eventually blur the ethical and moral boundaries between compensated egg sharing and commercialized oocyte donation

Compensated egg sharing was originally conceived as a patient self-help co-operative scheme to avoid overt 'commodification' of donor oocytes and prevent doctors and medical institutions from acting as 'brokers' of donated human material. As such, egg sharing is an ethically justifiable and much-preferred alternative to commercialized oocyte donation. However, recent advances in oocyte cryopreservation technology are likely to blur the ethical and moral boundaries between compensated egg sharing and commercialized oocyte donation. The banking of cryopreserved oocytes would negate the requirement for donors and recipients in egg sharing to have co-ordinated and synchronized treatment cycles. Instead, fertility doctors and medical institutions can now offer subsidized fertility treatment upfront to any patient willing to donate a portion of her retrieved cohort of oocytes for banking and subsequent donation. Thus, more opportunity is now open for them to act as 'middle-man' to broker the transaction of oocytes between donor and recipient, which would inevitably result in overt 'commodification' of donated human material. Administrative and processing fees will de finitely be billed to prospective recipients, for banking and storage of the cryopreserved oocytes, which would mean that a direct profit can now be made from the transaction of oocytes between donor and recipient.

Cryopreservation of unfertilized human oocytes

Previous investigations revealed that choline-based freezing media developed in our laboratory were superior to conventional sodium-based media for storing mouse oocytes. This paper examines the ability of the choline-based medium CJ2 and a modified form of this medium, CJ3, to cryopreserve unfertilized human oocytes. Oocytes that were consented for research and matured overnight, as well as freshly collected, donor, mature metaphase II (MII) oocytes, were cryopreserved using choline-based media and an optimized slow-cooling protocol. The results showed higher survival and fertilization rates when CJ3 supplemented with 0.2 mmol/l sucrose was used as compared with CJ2 supplemented with either 0.1 mmol/l or 0.2 mmol/l sucrose. Freshly collected oocytes were more difficult to cryopreserve than those matured in vitro. Modification of the base medium proved to be one of the key factors in obtaining survival rates over 90%. Fertilization rates, embryo development, and genetic analysis of embryos resulting from control and frozen-thawed oocytes are provided. There appears to be a high correlation between chromosomal anomalies and abnormal morphology in embryos from thawed oocytes.

Are programmable freezers still needed in the embryo laboratory? Review on vitrification

The predictable answer to the provocative question of whether programmable freezers are still needed in the embryo laboratory is an even more provocative 'no'. However, such a radical statement needs strong support. Based on the extensive literature of the past 5 years, the authors collected arguments either supporting or contradicting their opinion. After an overview of the causes of cryoinjuries and strategies to eliminate them, the evolution of vitrification methods is discussed. Special attention is paid to the biosafety issues. The authors did not find any circumstance in oocyte or embryo cryopreservation where slow freezing offers considerable advantages compared with vitrification. In contrast, the overwhelming majority of published data prove that the latest vitrification methods are more efficient and reliable than any version of slow freezing. Application of the proper vitrification methods increases the efficiency of long-term storage of stem cells and opens new perspectives in cryopreservation of oocytes, both for IVF and somatic cell nuclear transfer. However, lack of support from regulatory authorities, and conservative approachs regarding novel techniques can slow down the implementation of vitrification. The opinion of the authors is that vitrification is the future of cryopreservation. The public have the final say in whether they want and allow this future to arrive.

Improving cryopreservation systems

Cryopreservation of oocytes and embryos is a crucial step for widespread practical application of other techniques in domestic animal embryology. However, in contrast to the rapid development of procedures in the eighties and early nineties of the last century, new advancements with profound practical consequences have only been recently achieved. As a result of a long and controversial development, an alternative group of methods, vitrification, has proved its efficiency and practicality in the past few years. The aim of this short review is to characterize strategies to prevent cryoinjuries, summarize the development of vitrification, overview its recent achievements, and provide a perspective about possible application. Authors strongly believe that the future of mammalian oocyte and embryo cryopreservation will be mainly based on vitrification, and the rate of advancement will be determined by the rate by which embryologists learn and acknowledge this new approach.

Fertility preservation and reproduction in cancer patients

Cancer treatment often results in reduced fertility. Cancer patients should be informed of options for fertility preservation and future reproduction prior to cancer treatment. Reproduction in the context of cancer raises a number of ethical issues related to both patient and offspring welfare.

Comparison of the survival of human biopsied embryos after cryopreservation with four different methods using non-transferable embryos

BACKGROUND

The standard embryo cryopreservation method is still less than optimal for biopsied embryos. The aim of this study was to compare the survival of biopsied embryos cryopreserved with four different methods using non-transferable embryos.

METHODS

Abnormal embryos from one or three pronuclei and spare embryos of grade 3 and 4 were used for this study. Non-biopsied embryos were cryopreserved using the standard method as control. Biopsied embryos were cryopreserved using four methods as follows: standard method, modified freezing method, modified thawing method and vitrification. Blastomere survival and blastulation of frozen-thawed embryos were compared between the different methods.

RESULTS

The proportion of embryos with > or = 50% blastomere survival and total blastomere survival rate of biopsied embryos were significantly higher with vitrification than the other three methods. Both the modified freezing and modified thawing methods had significantly higher embryo survival and total blastomere survival rates than standard methods. However, there was no significant difference in blastulation of surviving embryos in all the five groups.

CONCLUSIONS

Non-transferable embryos derived from clinical IVF/ICSI are useful for evaluation of the optimal freezing procedures for biopsied embryos. Vitrification increases the survival rate of human biopsied embryos above standard and modified cryopreservation methods.

Healthy girl born after cryopreservation of gametes and ICSI in a patient with seminoma

This study reports birth in a case of intracytoplasmic sperm injection with cryopreserved oocytes and spermatozoa banked after radiotherapy and prior to chemotherapy due the occurrence of two non-synchronous seminomas. A 30-year-old male with a diagnosis of seminoma cryopreserved six vials of spermatozoa. After oncological treatment was completed, his partner, a 24-year-old woman, underwent ovarian stimulation. Seventeen oocytes were retrieved; one was at the germinal vesicle stage and two were injected, resulting in two embryos. Fourteen metaphase II oocytes were frozen. The woman presented moderated ovarian hyperstimulation syndrome, and embryo cryopreservation was indicated. After endometrial preparation, two embryos were transferred and a pregnancy was achieved. The woman suffered eclampsia during week 28 of gestation. Caesarean section was performed and a preterm girl weighing 1000 g was born, but died 2 weeks after delivery. A year later, a second procedure was begun. Frozen oocytes and one vial of semen were thawed. Eight of the 14 oocytes survived and were microinjected; two became fertilized and one good quality cleaved embryo was transferred. Pregnancy was achieved and a healthy girl was born with a birth weight of 2800 g. Oocyte cryopreservation associated with sperm banking in cancer patients is a useful tool for couples seeking deferred parenthood.

Fundamentals of cryobiology in reproductive medicine

The aim of this review will be to provide a basic understanding of the biophysical processes that accompany the application of cryopreservation in reproductive medicine. The ability to store cells in 'suspended animation' outside the body has become a keystone practice in the development of many modern clinical therapies, and, in fact, the sciences of cryobiology and IVF have developed in parallel over the past 50 years. During this time, some of the underlying principles of the quantitative biophysical aspects of cryobiology have been clarified. Water is the universal biocompatible solvent, but also possesses unique properties for stability of living cells. Whilst low temperatures themselves have defined effects on cell structure and function, it is the phase transition of water to ice that is the most profound challenge for survival. The thermodynamics of dilute aqueous solutions dictate how cells and tissues respond to the freezing process. Current concepts of nucleation, ice crystal growth and solute exclusion from the ice lattice will be discussed to illustrate what cells must negotiate to avoid lethal damage, and the role of cryoprotectants in enhancing recovery. Quantitative formalisms now exist to model and predict how water and solutes move across cell membranes before and during freezing, or how nucleation events will proceed, and these will be outlined. Cryoprotectants have both positive and negative effects on cell function depending on the kinetics of exposure. The concept of tolerable osmotic excursion of cell volume will be discussed, along with the evidence for a 'pseudo-glassy' state for cells during traditional cryopreservation. This will be compared with the recent interest in promoting glassy states in the whole sample using vitrification protocols, outlining the advantages and drawbacks of each approach. Additional methods for controlling ice nucleation have a role to play here, and a brief outline of current technologies will be given. Finally, issues of safety and stability of cryopreserved samples will be set out.