Three live births after human embryo vitrification with the use of aluminum oxide as an intermediate cooling agent: a case report

Objective

To study the possibility of increasing the cooling rates of the vitrification procedure in a closed system with the use of aluminum oxide as an intermediate coolant.

Design

Case report.

Subjects

Six patients undergoing procedures for assisted reproduction.

Intervention

Comparative studies of cryopreservation of donor embryos with aluminum oxide as an intermediate cooling agent (experimental group) and without it (control group) have been performed. After thawing, the embryo morphology and its potential to develop to the blastocyst stage have been assessed. The methodology was then applied to clinical practice.

Main Outcome Measures

Twenty embryos of 6 patients have been vitrified on day 4 after fertilization with the use of aluminum oxide as an intermediate coolant. Fourteen of them have been thawed. All have displayed normal morphology and 10 have formed blastocysts after 24 hours of culture. Four of the patients received embryo transfer with 2 embryos and the other 2 with single embryos.

Results

After preliminary comparative studies of embryos frozen with aluminum oxide and a control group, the results showed no statistically significant difference between their quality and potential to reach to blastocyst stage. That gave us ground to apply the methodology in clinical practice. After the embryo transfer, 3 clinical pregnancies with successful live births have been obtained.

Conclusions

Our experience shows that preimplantation embryos can be cryopreserved aseptically, in closed systems, with the help of aluminum oxide as an intermediate coolant.

Vitrification and in-straw warming do not affect pregnancy rates of biopsied bovine embryos

In the cattle industry, in vivo or in vitro embryo production combined with genotyping and cryopreservation technologies allows the selection and conservation of embryos carrying genes for desirable traits. This study aimed to assess the efficiency of a vitrification method suitable for in-straw warming of biopsied in vivo derived (IVD) bovine embryos. Three experiments were carried out using two methodologies: the Cryotop®, the gold standard vitrification and 3-step warming methodology, or the VitTrans, a vitrification/in-straw 1-step warming method that enables direct embryo transfer to the uterus. In experiment 1, intact and biopsied in vitro produced (IVP) day 7 expanded blastocysts were vitrified using the Cryotop® and warmed in 1- or 3-steps. No differences in survival rates were recorded at 24 h after warming for intact or biopsied IVP blastocysts irrespective of the warming procedure. In experiment 2, the effect of the time from trophectoderm (TE) biopsy to vitrification/in-straw warming on post-warming survival rate was assessed. No significant differences in survival were observed when blastocysts were vitrified/in-straw warmed immediately after biopsy or after 3 h in culture when compared to intact blastocysts. In experiment 3, IVD embryos were vitrified 3 h after biopsy using the Cryotop® or the VitTrans method and pregnancy rates were assessed at day 60 after transfer. Fresh, biopsied embryos served as control. Similar pregnancy rates were observed when IVD biopsied embryos were transferred fresh or vitrified/warmed by the Cryotop® or VitTrans method. No significant effect of the embryo quality or developmental stage was detected on the percentage of pregnant recipients when IVD biopsied embryos were transferred fresh or after vitrification. While fresh female IVD embryos produced significantly higher pregnancy rates than male embryos, there were no differences in pregnancy rates when male or female vitrified/warmed embryos were transferred. About 81% from the biopsies analyzed successfully determined the embryo sex, confirming that DNA was there, and it was efficiently amplified. To conclude, our findings indicate that both vitrification methodologies produced similar post-warming outcomes for both intact and biopsied IVP embryos. Besides, vitrification/in-straw warming of biopsied IVD bovine embryos did not affect the viability to originate pregnancy, being a useful option for their direct transfer in field conditions.

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

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

Low cryoprotectant concentration rapid vitrification of mouse oocytes and embryos

Vitrification of mammalian oocytes and embryos is typically a two-step procedure involving two solutions of increasing concentrations of cryoprotectants. In the present study, we report a simple vitrification protocol that uses low cryoprotectant concentration and a single medium (LCSM). This medium, along with the traditional high concentration two media (HCTM) protocol, was used to vitrify mouse oocytes, zygotes, and blastocysts using silica capillary, cryotop, cryolock, and 0.25 ml straws. Survival rates, two-cell rates, and blastocyst formation rates were compared for oocytes and zygotes vitrified using both protocols. Results show that the LCSM protocol was as good as or better than the traditional HCTM protocol for vitrifying mouse MII oocytes and zygotes using silica capillary, cryotop, and cryolock. On the other hand, for blastocysts, only silica capillary using LCSM had comparable results with the traditional HCTM protocol while cryolock and cryotop had significantly lower percentages of re-expanded and hatched blastocysts. Collapsing blastocysts prior to vitrification or longer duration for better cryoprotectant distribution in multicellular embryos may improve the outcome. In conclusion, the LCSM protocol, with one medium of much lower cryoprotectant concentrations and shorter equilibration time, reduces exposure to cryoprotectant toxicity while improves efficiency, consistency and reliability for mammalian oocyte and embryo preservation.

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification.

Dual Suppression Effect of Magnetic Induction Heating and Microencapsulation on Ice Crystallization Enables Low-Cryoprotectant Vitrification of Stem Cell-Alginate Hydrogel Constructs

Stem cells microencapsulated in hydrogel as stem cell-hydrogel constructs have wide applications in the burgeoning cell-based medicine. Due to their short shelf life at ambient temperature, long-term storage or banking of the constructs is essential to the "off-the-shelf" ready availability needed for their widespread applications. As a high-efficiency, easy-to-operate, low-toxicity, and low-cost method for long-term storage of the constructs, low-cryoprotectant (CPA) vitrification has attracted tremendous attention recently. However, we found many cells in the stem cell-alginate constructs (∼500 μm in diameter) could not attach to the substrate post low-CPA vitrification with ∼2 M penetrating CPAs. To address this problem, we introduced nanowarming via magnetic induction heating (MIH) of Fe3O4 nanoparticles to minimize recrystallization and devitrification during the warming step of the low-CPA vitrification procedure. Our results indicate that high-quality stem cell-alginate hydrogel constructs with an intact microstructure, high immediate cell survival (>80%), and greatly improved attachment efficiency (by nearly three times, 68% versus 24%) of the encapsulated cells could be obtained post-cryopreservation with nanowarming. Moreover, the cells encapsulated in the cell-hydrogel constructs post-cryopreservation maintained normal proliferation under 3D culture and retained intact biological function of multilineage differentiation. This novel low-CPA vitrification approach for cell cryopreservation enabled by the combined use of alginate hydrogel microencapsulation and Fe3O4 nanoparticles-mediated nanowarming may be valuable in facilitating the widespread application of stem cells in the clinic.

Ice nucleating agents allow embryo freezing without manual seeding

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy).

Cryopreservation of Luciola praeusta Kiesenwetter (Coleoptera: Lampyridae) embryos by vitrification

There is an urgent need to preserve the ever-decreasing number of different species of fireflies all over the world. We sought to develop a vitrification procedure to cryopreserve the firefly embryos. The late stages of Luciola praeusta Kiesenwetter embryos were collected. Several impermeable and permeable protectants with various concentrations in different mediums (TNM-FH insect medium, Grace's medium, Dulbecco's Modification of Eagle's Medium (DMEM) and Dulbecco's Phosphate-Buffered Saline (DPBS)) were used. Embryos culturing in TNM-FH medium yielded the highest survival rate of 75.3 ± 3.6%. One-step, two-step and three-step methods were used in equilibrium procedure respectively. The highest survival rate (73.7% ±3.2%) occurred in embryos treated by three-step method ((1.5 M ethylene glycol (EG) + 2 M EG plus 8% polyvinylpyrrolidone (PVP) + 3 M EG, 8% PVP and 15% trehalose). Additionally, embryos exposed to 0.5 M trehalose presented a significantly higher survival rate (71.8 ± 2.7%) than embryos preserved in 0.5 M sucrose.

Advances in reproductive biotechnologies

In recent times, reproductive biotechnologies have emerged and started to replace the conventional techniques. It is noteworthy that for sustained livestock productivity, it is imperative to start using these techniques for facing the increasing challenges for productivity, reproduction and health with impending environment conditions. These recent biotechniques, both in male and female, have revolutionized and opened avenues for studying and manipulating the reproductive process both in vitro and in vivo in various livestock species for improving tis efficiency. This review attempts to highlight pros and cons, on the recent developments in reproductive biotechnologies, both in male and female in livestock species.

Cryopreservation of oocytes and embryos

Two hundred years have passed since the first description of supercooled water by Gey-Lussac to the recently high survival rates of embryo and oocytes after vitrification. This review discusses important milestones that have made vitrification the method of choice for oocytes and embryos cryopreservation. We will go through the first cells ever to survive low temperature exposure in the beginning of the last century, the finding of glycerol in the late 1940s and the first mouse and bovine embryos freezing in the 1970s. During the 1980s, embryo vitrification began and the time since is a tribute to the development of oocytes vitrification. Standardization and an automatic vitrification procedure are currently under development. The next evolutionary step in oocyte and embryo cryopreservation will be preserving them in the dry state at room temperature, allowing home storage for future use a reality.

Extreme rapid warming yields high functional survivals of vitrified 8-cell mouse embryos even when suspended in a half-strength vitrification solution and cooled at moderate rates to -196°C

To cryopreserve cells, it is essential to avoid intracellular ice formation during cooling and warming. One way to do so is to subject them to procedures that convert cell water into a non-crystalline glass. Current belief is that to achieve this vitrification, cells must be suspended in very high concentrations of glass-inducing solutes (i.e., ≥6 molal) and cooled at very high rates (i.e., ≫1000°C/min). We report here that both these beliefs are incorrect with respect to the vitrification of 8-cell mouse embryos. In this study, precompaction 8-cell embryos were vitrified in several dilutions of EAFS10/10 using various cooling rates and warming rates. Survival was based on morphology, osmotic functionality, and on the ability to develop to expanded blastocysts. With a warming rate of 117,500°C/min, the percentages of embryos vitrified in 1×, 0.75×, and 0.5× EAFS that developed to blastocysts were 93%, 92%, and 83%, respectively. And the percentages of morphological survivors that developed to expanded blastocysts were 100%, 92%, and 97%, respectively. Even when the solute concentration of the EAFS was reduced to 33% of normal, we obtained 40% functional survival of these 8-cell embryos.

Development of a modified straw method for vitrification of in vitro-produced bovine blastocysts and various genes expression in between the methods

This study evaluated a modified plastic straw loading method for vitrification of in vitro-produced bovine blastocysts. A modified straw was used with a depressed area on its inner surface to which embryos attach. In vitro-produced blastocysts were randomly assigned into three groups: (i) blastocysts attached to the inner surface of a plastic straw (aV), (ii) blastocysts attached to the inner surface of a modified plastic straw (maV), and (iii) non-vitrified blastocysts (control). The recovery rates were not significantly different between aV and maV groups (95.8% vs. 94.3%). The post-thaw survival rate did not significantly differ between aV and maV groups (86.4% vs. 88.2%). The total cell numbers of blastocyst was higher in control than in aV and maV groups (142 ± 21.8 vs. 117 ± 29.7 and 120 ± 25.2; P < 0.05), but not significantly differ between aV and maV groups. The mRNA levels of pro-apoptosis related genes Bax and Caspase-3 were higher in aV and maV than in control (P < 0.05). By contrast, the mRNA levels of anti-apoptotic genes Bcl-2 and Mcl-1 and of antioxidant-related genes MnSOD and Prdx5 were lower in aV and maV than in control (P < 0.05). Confocal microscopy analysis of Golgi apparatus and mitochondria showed that the fluorescence intensity of Golgi apparatus and mitochondria was higher in control than in aV and maV groups. In conclusion, both aV and maV methods can be used to successfully vitrify IVP blastocysts, with maV method to be preferable because of its easiness in embryo loading.

Porcine oocyte vitrification in optimized low toxicity solution with open pulled straws

One of the greatest challenges for reproductive cryobiologists today is to develop an efficient cryopreservation method for human and domestic animal oocytes. The objective of the present study was to optimize a low toxicity solution called VM3 to vitrify porcine oocytes using an open pulled straw (OPS) device and to evaluate the effects on viability, chromosomal organization and cortical granules distribution. Two experiments were conducted in this study. Firstly, we determined the minimum concentration of cryoprotectant present in the VM3 solution required (7.6 M) for vitrification using an OPS device. The appearance of opacity was observed when using a cooling solution at –196°C; no observable opacity was noted as vitrification. In addition, the ultrastructure of oocytes in VM3 or VM3 optimized solution was examined using cryo-scanning electron microscopy. The minimum total cryoprotectant concentration present in VM3 solution necessary for apparent vitrification was 5.6 M when combined with use of an OPS device. Use of both vitrification solutions showed a characteristic plasticized surface. In the second experiment, the relative cytotoxicity of vitrification solutions (VM3 and VM3 optimized) was studied. Oocyte viability, chromosomal organization and the cortical granules distribution were assessed by fluorescent stain. After warming, oocyte survival rate was similar to that of fresh oocytes. The vitrification process significantly reduced correct chromosomal organization and cortical granules distribution rates compared with the fresh oocytes group. However, correct chromosomal organization and cortical granules distribution rates did not differ among oocytes placed in different vitrification solutions. In conclusion, our data demonstrated that the VM3 solution can be optimized and that reduction in concentration to 5.6 M enabled vitrification of oocytes with an OPS device, however use of the VM3 optimised solution had no beneficial effect on vitrification of porcine oocytes.

Ultra-rapid warming yields high survival of mouse oocytes cooled to -196°c in dilutions of a standard vitrification solution

Intracellular ice is generally lethal. One way to avoid it is to vitrify cells; that is, to convert cell water to a glass rather than to ice. The belief has been that this requires both the cooling rate and the concentration of glass-inducing solutes be very high. But high solute concentrations can themselves be damaging. However, the findings we report here on the vitrification of mouse oocytes are not in accord with the first belief that cooling needs to be extremely rapid. The important requirement is that the warming rate be extremely high. We subjected mouse oocytes in the vitrification solution EAFS 10/10 to vitrification procedures using a broad range of cooling and warming rates. Morphological survivals exceeded 80% when they were warmed at the highest rate (117,000°C/min) even when the prior cooling rate was as low as 880°C/min. Functional survival was >81% and 54% with the highest warming rate after cooling at 69,000 and 880°C/min, respectively. Our findings are also contrary to the second belief. We show that a high percentage of mouse oocytes survive vitrification in media that contain only half the usual concentration of solutes, provided they are warmed extremely rapidly; that is, >100,000°C/min. Again, the cooling rate is of less consequence.

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.

Production of F₁ offspring with vitrified sperm from a live-bearing fish, the green swordtail Xiphophorus hellerii

This study reports the first production of offspring with vitrified sperm from a live-bearing fish Xiphophorus hellerii. The overall goal of this study was to develop streamlined protocols for integration into a standardized approach for vitrification of aquatic species germplasm. The objectives were to (1) estimate acute toxicity of cryoprotectants, (2) evaluate vitrification solutions, (3) compare different thawing methods, (4) evaluate membrane integrity of post-thaw sperm vitrified in different cryoprotectants, and (5) evaluate the fertility of vitrified sperm. Nine cryoprotectants and two commercial vitrification additives were tested for acute toxicity and glass forming ability, alone and in combination. Two vitrification solutions, 40% glycerol (Gly) and 20% Gly+20% ethylene glycol (EG) in 500 mOsmol/kg Hanks' balanced salt solution (HBSS), were selected for vitrification of 10 μL sperm samples using inoculating loops plunged into liquid nitrogen. Samples were thawed at 24°C (one loop in 5 μL of HBSS or three loops in 500 μL of HBSS). Samples thawed in 500 μL were concentrated by centrifugation (1000 g for 5 min at 4°C) into 5 μL for artificial insemination. Offspring were produced from virgin females inseminated with sperm vitrified with 20% Gly+20% EG and concentrated by centrifugation.

Clinical application of oocyte vitrification: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

To perform a systematic review of the literature to identify randomized controlled trials assessing the efficacy of oocyte vitrification in terms of oocyte survival, fertilization, embryo development, and pregnancy rates.

DESIGN

Systematic review and meta-analysis of randomized controlled trials.

SETTING

Private university-affiliated IVF center, university-based hospital.

PATIENT(S)

Patients recruited in randomized controlled trials considering oocyte vitrification as one of the experimental arms and slow freezing or fresh oocytes control as the other.

INTERVENTION(S)

Vitrification of human oocytes vs. slow freezing or fresh oocytes.

MAIN OUTCOME MEASURE(S)

Ongoing pregnancy rate; secondary outcomes were clinical pregnancy rate, implantation rate, embryo development, fertilization rate, and oocyte survival.

RESULT(S)

Five eligible studies were finally included. They involved 4,282 vitrified oocytes, 3,524 fresh oocytes, and 361 slow-frozen oocytes between 2005 and 2009. The rates of ongoing pregnancy, top-quality embryo, embryo cleavage, and fertilization did not differ between the vitrification and the fresh oocyte groups. The oocyte survival rate was higher in vitrified vs. slow-frozen oocytes (odds ratio [OR] 2.46, 95% confidence interval [CI] 1.82-3.32), although heterogeneity between studies was observed. The fertilization rate was higher in vitrified vs. slow-frozen oocytes (OR 1.50, 95% CI 1.07-2.11). Vitrification also resulted in a higher rate top-quality embryo (22.4% vs. 8.0%, OR 3.32, 95% CI 1.37-8.02) and embryo cleavage rate (day 2: 64.6% vs. 47.7%, OR 2.00, 95% CI 1.33-3.00; day 3: 53.0% vs. 33.3%, OR 2.25, 95% CI 1.32-3.85) as compared with slow freezing.

CONCLUSION(S)

Vitrification is an efficient method to preserve oocytes, although more large controlled clinical trials are needed to strengthen this conclusion.

Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification

Preservation of female genetics is currently done primarily by means of oocyte and embryo cryopreservation. The field has seen much progress during its four-decade history, progress driven predominantly by research in humans, cows, and mice. Two basic cryopreservation techniques rule the field – controlled-rate freezing, the first to be developed, and vitrification, which, in recent years, has gained a foothold. While much progress has been achieved in human medicine, the cattle industry, and in laboratory animals, this is far from being the case for most other mammals and even less so for other vertebrates. The major strides and obstacles in human and other vertebrate oocyte and embryo cryopreservation will be reviewed here.

Can fresh embryo transfers be replaced by cryopreserved-thawed embryo transfers in assisted reproductive cycles? A randomized controlled trial

PURPOSE

Controlled ovarian hyperstimulation has been shown to advance endometrial maturation and adversely affects implantation in ART. It has been reported that there is a better embryo-endometrium synchrony in frozen-thawed embryo transfer cycles than fresh embryo transfer cycles. The objective of this study was to compare ongoing pregnancy rates between fresh ET and FET cycles.

METHODS

In an open prospective, controlled study, the patients who were classified as high responders, were randomized to either fresh ET or FET. The embryos in FET group were cryopreserved with vitrification by Cryotop method.

RESULTS

A total of 374 patients were included, 187 of which were randomized to FET and 187 to fresh ET. There were 39% (n = 73) ongoing pregnancy in FET group compared with 27.8% (n = 52) in fresh ET group[odds ratio = 1.66;95% confidence interval = 1.07-2.56; p = 0.02].

CONCLUSIONS

FETs can be performed instead of fresh ETs to improve the outcome of ART in highly selected patients.

Ultra-rapid vitrification of mouse oocytes in low cryoprotectant concentrations

The ideal cryopreservation protocol would combine the benefits of slow freezing with the benefits of vitrification. This report describes a method for the ultra-rapid vitrification of oocytes using slush nitrogen in quartz capillaries. The approach minimizes the thermal mass of the vitrification vessel by using open microcapillaries made of highly conductive quartz and achieves cooling rates of 250,000 degrees C/min. The process of vitrification can be optimized by maximizing the rate at which the sample is cooled, which allows for the use of lower cryoprotectant concentrations. Mouse oocytes can be successfully vitrified using 1.5 mol/l 1,2-propanediol and 0.5 mol/l trehalose and achieve survival rates of 90.0%(36/40). Fertilization and blastocyst formation rates of vitrified-warmed and fresh oocytes were not significantly different. A total of 120 blastocysts from each of the vitrified-warmed and fresh oocytes were transferred to surrogate mothers and 23 and 27 offspring were born respectively. All offspring in both groups were healthy, grew and bred normally and gave rise to a second generation of pups. Thus, an ultra-rapid vitrification technique has been developed for mouse oocytes that uses low concentrations of cryoprotectants and slush nitrogen in quartz capillaries, which combines the benefits of slow freezing and vitrification.

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.