Effect of different cryopreservation protocols on the metaphase II spindle in human oocytes

Employer-based insurance coverage increases utilization of planned oocyte cryopreservation

PURPOSE

To determine the utilization of planned oocyte cryopreservation (OC) in the year immediately prior to, and the year of, insurance coverage commencement for employees at our institution.

METHODS

Patient demographics and cycle outcomes were retrospectively compared between the first OC cycles occurring in 2017 vs. 2018 according to insurance coverage and type, age, and the number of oocytes retrieved and cryopreserved. Continuous demographic variables including age, BMI, day 3 FSH and E2, AMH, gravidity, and parity were compared using student T-tests. Cycle outcomes, including the number of oocytes retrieved and cryopreserved were compared using linear regression models, adjusting for potential confounders including age, BMI, and ovarian reserve parameters.

RESULTS

Between January 2017 and December 2018, 123 patients underwent planned OC at our institution. Patient age ranged from 23 to 44 years and did not significantly differ from 2017 to 2018 (mean 34.9 vs. 35.2). There was a 12% increase in planned OC utilization from 2017 (N = 58) to 2018 (N = 65). Significantly, more patients had any insurance coverage in 2018 vs. 2017 (71.9% vs. 40.4%, p = 0.001), a 78% increase. From 2017 to 2018, the number of patients with hospital-based insurance coverage undergoing planned OC increased by a factor of 8 (5 to 41.5%, p < 0.001), while the number of self-pay patients significantly decreased (p = 0.001). No differences were found regarding cycle outcomes.

CONCLUSION

A greater proportion of women at our institution had insurance coverage for planned OC in 2018 vs. 2017. Employer-based insurance coverage for planned OC was associated with a significant increase in utilization by hospital employees.

Chromosome Segregation in the Oocyte: What Goes Wrong during Aging

Human female fertility and reproductive lifespan decrease significantly with age, resulting in an extended post-reproductive period. The central dogma in human female reproduction contains two important aspects. One is the pool of oocytes in the human ovary (the ovarian reserve; approximately 10⁶ at birth), which diminishes throughout life until menopause around the age of 50 (approximately 10³ oocytes) in women. The second is the quality of oocytes, including the correctness of meiotic divisions, among other factors. Notably, the increased rate of sub- and infertility, aneuploidy, miscarriages, and birth defects are associated with advanced maternal age, especially in women above 35 years of age. This postponement is also relevant for human evolution; decades ago, the female aging-related fertility drop was not as important as it is today because women were having their children at a younger age. Spindle assembly is crucial for chromosome segregation during each cell division and oocyte maturation, making it an important event for euploidy. Consequently, aberrations in this segregation process, especially during the first meiotic division in human eggs, can lead to implantation failure or spontaneous abortion. Today, human reproductive medicine is also facing a high prevalence of aneuploidy, even in young females. However, the shift in the reproductive phase of humans and the strong increase in errors make the problem much more dramatic at later stages of the female reproductive phase. Aneuploidy in human eggs could be the result of the non-disjunction of entire chromosomes or sister chromatids during oocyte meiosis, but partial or segmental aneuploidies are also relevant. In this review, we intend to describe the relevance of the spindle apparatus during oocyte maturation for proper chromosome segregation in the context of maternal aging and the female reproductive lifespan.

Improved developmental potential of mouse vitrified-warmed oocytes achieved by culturing in recovery medium with glutathione ethyl ester (GSH-OEt)

PURPOSE

The aim of the present study was to investigate the effect of glutathione ethyl ester (GSH-OEt) in the recovery medium on the developmental competence of mouse vitrified-warmed MII oocytes.

METHODS

Vitrified-warmed oocytes were incubated for 1 h in recovery medium in the presence or absence of 0.5 mM GSH-OEt. The authors examined the effects of GSH-OEt, first on the levels of glutathione (GSH) and reactive oxygen species (ROS) in vitrified-warmed oocytes, and second, on in vitro blastocyst development, division speed to blastocysts, and total cell numbers of blastocysts from vitrified-warmed oocytes fertilized by Intracytoplasmic sperm injection (ICSI).

RESULTS

Adding GSH-OEt to the recovery medium significantly (p < 0.05) increased GSH content and decreased ROS levels in vitrified-warmed oocytes. The blastocyst rate did not differ significantly between the two groups, but the speed of development to blastocysts in the GSH-OEt (+) group was significantly more rapid. In addition, the total blastocyst cell number was significantly higher in the GSH-OEt (+) group than in the GSH-OEt (-) group (92.8 ± 5.1 vs. 71.4 ± 3.5, p < 0.01).

CONCLUSION

Adding GSH-OEt to the recovery medium of vitrified-warmed mouse oocytes enhances the development potential of oocytes and improves the quality of blastocysts.

Elective oocyte cryopreservation for age-related fertility decline

PURPOSE

Women who pursue fertility at an advanced age are increasingly common. Family planning and sexual education have traditionally focused on contraception and prevention of sexually transmitted diseases. A focus should now also be placed on fertility awareness and fertility preservation. This manuscript aims to give an update on the existing evidence around elective oocyte cryopreservation, also highlighting the need for fertility education and evidence-based, individualized counselling.

METHODS

A thorough electronic search was performed from the start of databases to March 2020 aiming to summarize the existing evidence around elective egg freezing, the logic behind its use, patient counselling and education, success rates and risks involved, regulation, cost-effectiveness, current status and future perspectives.

RESULTS

Clinician-led counselling regarding reproductive aging and fertility preservation is often overlooked. Elective oocyte cryopreservation is not a guarantee of live birth, and the answer regarding cost-effectiveness needs to be individualized. The existing studies on obstetric and perinatal outcomes following the use of egg freezing are, until now, reassuring. Constant monitoring of short-term and long-term outcomes, uniform regulation and evidence-based, individualized counselling is of paramount importance.

CONCLUSIONS

Elective oocyte cryopreservation is one of the most controversial aspects of the world of assisted reproduction, and a lot of questions remain unanswered. However, women today do have this option which was not available in the past. Elective oocyte cryopreservation for age-related fertility decline should be incorporated in women's reproductive options to ensure informed decisions and reproductive autonomy.

Impact of Maturation and Vitrification Time of Human GV Oocytes on the Metaphase Plate Configuration

The combination of in vitro maturation (IVM) techniques and oocyte vitrification (OV) could increase the number of useful oocytes in different types of patients. IVM and subsequent OV is the most widely used clinical strategy. Would the results improve if we reverse the order of the techniques? Here, we evaluated survival, in vitro maturation, time to extrude the first polar body (PB), and the metaphase plate configuration of human prophase I (GV) oocytes before or after their vitrification. Specific, 195 GV oocytes from 104 patients subjected to controlled ovarian stimulation cycles were included. We stablished three experimental groups: GV oocytes vitrified and IVM (Group GV-Vit), GV oocytes IVM and vitrified at MII stage (Group MII-Vit), and GV oocytes IVM (Group not-Vit). All of them were in vitro matured for a maximum of 48 h and fixed to study the metaphase plate by confocal microscopy. According to our results, the vitrification of immature oocytes and their subsequent maturation presented similar survival, maturation, and metaphase plate conformation rates, but a significantly higher percentage of normal spindle than the standard strategy. Additionally, the extension of IVM time to 48 h did not seem to negatively affect the oocyte metaphase plate configuration.

Cumulus cell gene expression in luteal-phase-derived oocytes after double stimulation in one menstrual cycle

RESEARCH QUESTION

Does double stimulation (DuoStim) affect cumulus cell gene expression in luteal-phase-derived oocytes?

DESIGN

This prospective observational study included 39 patients with reduced ovarian reserve. Fifteen patients (group 1) underwent IVF with a gonadotrophin-releasing hormone antagonist in the follicular phase and 24 patients (group 2) underwent DuoStim. A total of 149 cumulus cell samples were divided into two groups according to the phase of the cycle: group 1 included 55 follicular-phase-derived oocytes and group 2 included 94 luteal-phase-derived oocytes. The expression levels of the following genes were assessed using quantitative polymerase chain reaction: HAS2, VCAN, ALCAM, PTGS2, GREM1, ITPKA, TRPM7, SDC4, CALM2, SPSB2, TP53I3, PGR and PFKP.

RESULTS

The expression of 10 out of 13 genes in cumulus cells was similar between DuoStim luteal-phase-derived oocytes and follicular-phase-derived oocytes. A significant increase in the mRNA levels of VCAN (15.542 ± 6.8 versus 20.353 ± 10.58; P = 0.001), SDC4 (1.016 ± 0.65 versus 1.318 ± 0.97; P = 0.013), and TP53I3 (0.185 ± 0.09 versus 0.270 ± 0.11; P = 1.19E-05) was observed in group 2. The number of oocytes collected (5.57 ± 2.3 versus 5.7 ± 2.7; P > 0.05) and the number of blastocysts were comparable between the groups (2.1 ± 2.1 versus 2.7 ± 2.2; P > 0.05).

CONCLUSIONS

The DuoStim approach leads to changes in the follicular environment. It affects the expression levels of VCAN, SDC4, and TP53I3 in the cumulus cells of luteal-phase-derived oocytes. These results, however, did not correlate with oocyte maturation, embryo quality and pregnancy rate.

Anti-Müllerian hormone is an independent marker for oocyte survival after vitrification

RESEARCH QUESTION

This study explored the relationship between anti-Müllerian hormone (AMH) and oocyte survival after vitrification. The association between AMH and blastocyst formation after oocyte vitrification was also assessed.

DESIGN

A retrospective observational analysis was performed in a private IVF centre. A total of 4507 metaphase-II warmed oocytes were included from 450 couples, predominantly of Arab ethnicity. Between August 2015 and August 2018, couples underwent 484 intracytoplasmic sperm injection (ICSI) treatments using vitrified-warmed oocytes.

RESULTS

Patients' median age ± SD was 36.2 ± 6.1 years, AMH concentration 2.6 ± 3.4 ng/ml and body mass index (BMI) 26.5 ± 4.6 kg/m². The oocyte survival rate after vitrification was 87.37 ± 20.42%. AMH concentration showed a significant correlation (Kendall's tau 0.087, P = 0.0079) with oocyte survival rate independent of oocyte yield. Correlation was significant (odds ratio 1.041, 95% confidence interval 1.007-1.077, P = 0.018) when a multivariant model was applied that included AMH, age and BMI. The receiver operating characteristic curve showed an AMH cut-off value of 1.09 ng/ml that could obtain at least a 70% survival rate, with an area under the curve of 0.669. Regarding embryo development in ICSI cycles including fresh and warmed oocytes for the same patient, blastocyst formation rate was higher in fresh compared with warmed oocytes (P < 0.001). In this subgroup no significant correlation was seen between fertilization or blastocyst rate and AMH concentration.

CONCLUSIONS

AMH concentration showed a significant correlation with oocyte survival. Blastocyst formation was significantly lower after oocyte vitrification, but no correlation was found with AMH. Clinicians should carefully evaluate oocyte vitrification for patients with AMH below 1.09 ng/ml and consider embryo accumulation for these patients in preference to oocyte accumulation.

Postponing Pregnancy Through Oocyte Cryopreservation for Social Reasons: Considerations Regarding Clinical Practice and the Socio-Psychological and Bioethical Issues Involved

Oocyte freezing for 'social reasons' refers to women of reproductive age who are aiming to prolong, protect and secure their fertility. The term emerged to describe application of the highly promising technique, namely vitrification on oocytes retrieved through controlled ovarian stimulation (COS) from women intending to preserve their fertility for social reasons. These women opt to cryopreserve their oocytes at a point in their life when they need to postpone childbearing on the grounds of so called 'social' reasons. These reasons may include a highly driven career, absence of an adequate partner, financial instability, or personal reasons that make them feel unprepared for motherhood. This is a sensitive and multifaceted issue that entails medical, bioethical and socio-psychological components. The latest trend and the apparent increase noted on oocyte freezing for 'social reasons' has prompted our team of fertility specialists, embryologists, obstetricians, gynecologists and psychologists to proceed with a thorough, critical and all-inclusive comprehensive analysis. The wide range of findings of this analysis involve concerns of embryology and epigenetics that shape decisions made in the IVF laboratory, issues regarding obstetric and perinatal concerns on the pregnancy concluding from these oocytes and the respective delivery management and neonatal data, to the social and bioethical impact of this trend's application. This literature review refers to matters rising from the moment the 'idea' of this option is 'birthed' in a woman's thoughts, to proceeding and executing it clinically, up until the point of the pediatric follow up of the children born. We aim to shed light to the controversial issue of oocyte freezing, while objectively exhibit all aspects regarding this complex matter, as well as to respectfully approach how could the prospect of our future expectations be shaped from the impact of its application.

An improved method for vitrification of in vitro matured ovine oocytes; beneficial effects of Ethylene Glycol Tetraacetic acid, an intracellular calcium chelator

Vitrification affects fertilization ability and developmental competence of mammalian oocytes. This effect may be more closely associated with an intracellular calcium rise induced by cryoprotectants. The present study aimed to assess whether addition of Ethylene Glycol Tetraacetic acid (EGTA) to vitrification solution could improve quality and developmental competence of in vitro matured ovine oocytes. Vitrified groups were designed according to the presence or absence of EGTA and/or calcium in base media, including: mPB1+ (modified PBS with Ca²⁺), mPB1^- (modified PBS without Ca²⁺), mPB1⁺/EGTA (mPB1⁺ containing EGTA), mPB1^-/EGTA (mPB1^- containing EGTA). In vitro development, numerical chromosome abnormalities, hardening of zona pellucida, mitochondrial distribution and function of viable oocytes were evaluated and compared between groups. Quality of blastocysts was assessed by differential and TUNEL staining. Also, mRNA expression levels of six candidate genes (KIF11, KIF2C, CENP-E, KIF20A, KIF4A and KIF2A), were quantitatively evaluated by RT-PCR. Our results showed that calcium-free vitrification and EGTA supplementation can significantly increase the percentage of normal haploid oocytes and maintain normal distribution and function of mitochondria in vitrified ovine oocytes, consequently improving developmental rate after in vitro fertilization. qRT-PCR analysis showed no significant difference in mRNA expression levels of kinesin genes between vitrified and fresh oocytes. Also, the presence of calcium in vitrification solution significantly increased zona hardening. In conclusion, we have shown for the first time that supplementation of vitrification solution with EGTA, as a calcium chelator, improved the ability of vitrified ovine oocytes to preserve mitochondrial distribution and function, as well as normal chromosome segregation.

The Impact of Vitrification in Artificial Reproductive Technology Programmes

Cryopreservation is an integral part of the current methods of assisted reproductive technology (ART). In the past two decades, slow freezing has been replaced worldwide by vitrification due to its association with improved survival rates and clinical outcomes comparable to fresh embryo transfers. Successful embryo vitrification programmes have led to a significant reduction in the incidences of two major complications of ART: ovarian hyperstimulation syndrome and multiple gestations. Multiple embryo transfer cycles from the single ovum aspiration cycle have had a cumulative effect on the numbers of live births. Oocyte vitrification has also helped women to delay their pregnancies for medical or social reasons. This has made oocyte banking a viable option for better synchronisation of oocyte donation programmes. The emerging field of ovarian tissue vitrification has made fertility preservation possible for women undergoing gonadotoxic therapy. In this review, we have discussed the basic principles and methodology of slow freezing and vitrification along with its need and impact on ART.

The state of "freeze-for-all" in human ARTs

The recent development of vitrification technologies and the good outcomes obtained in assisted reproduction technologies have supported new indications for freezing and segmentation of treatment. Beyond OHSS prevention and avoidance of embryo transfers in the setting of an adverse endocrinological profile or endometrial cavity, we have witnessed a trend to shift fresh embryo transfers to frozen embryo transfers in many programs. We critically review the available evidence and suggest that freeze-all is not "for all," but should be individualized.

Improved cryotolerance and developmental potential of in vitro and in vivo matured mouse oocytes by supplementing with a glutathione donor prior to vitrification

STUDY QUESTION

Can supplementation of media with a glutathione (GSH) donor, glutathione ethyl ester (GEE), prior to vitrification protect the mouse oocyte from oxidative damage and critical changes in redox homeostasis, and thereby improve cryotolerance?

SUMMARY ANSWER

GEE supplementation supported redox regulation, rapid recovery of spindle and chromosome alignment after vitrification/warming and improved preimplantation development of mouse metaphase II (MII) oocytes.

WHAT IS KNOWN ALREADY

Cryopreservation may affect mitochondrial functionality, induce oxidative stress, and thereby affect spindle integrity, chromosome segregation and the quality of mammalian oocytes. GEE is a membrane permeable GSH donor that promoted fertilization and early embryonic development of macaque and bovine oocytes after IVM.

STUDY DESIGN, SIZE, DURATION

Two experimental groups consisted of (i) denuded mouse germinal vesicle (GV) oocytes that were matured in vitro in the presence or absence of 1 mM GEE (IVM group 1) and (ii) in vivo ovulated (IVO) MII oocytes that were isolated from the ampullae and exposed to 1 mM GEE for 1 h prior to vitrification (IVO group 2). Recovery of oocytes from both groups was followed after CryoTop vitrification/warming for up to 2 h and parthenogenetic activation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Reactive oxygen species (ROS), spindle morphology and chromosome alignment were analyzed by confocal laser scanning microscopy (CLSM) and polarization microscopy in control and GEE-supplemented MII oocytes. The relative overall intra-oocyte GSH content was assessed by analysis of monochlorobimane (MBC)-GSH adduct fluorescence in IVM MII oocytes. The GSH-dependent intra-mitochondrial redox potential (E^m_GSH) of IVM MII oocytes was determined after microinjection with specific mRNA at the GV stage to express a redox-sensitive probe within mitochondria (mito-Grx1-roGFP2). The absolute negative redox capacity (in millivolts) was determined by analysis of fluorescence of the oxidized versus the reduced form of sensor by CLSM and quantification according to Nernst equation. Proteome analysis was performed by quantitative 2D saturation gel electrophoresis (2D DIGE). Since microinjection and expression of redox sensor mRNA required removal of cumulus cells, and IVM of denuded mouse oocytes in group 1 induces zona hardening, the development to blastocysts was not assessed after IVF but instead after parthenogenetic activation of vitrified/warmed MII oocytes from both experimental groups.

MAIN RESULTS AND ROLE OF CHANCE

IVM of denuded mouse oocytes in the presence of 1 mM GEE significantly increased intra-oocyte GSH content. ROS was not increased by CryoTop vitrification but was significantly lower in the IVM GEE group compared to IVM without GEE before vitrification and after recovery from vitrification/warming (P < 0.001). Vitrification alone significantly increased the GSH-dependent intra-mitochondrial redox capacity after warming (E^m_GSH, P < 0.001) in IVM oocytes, presumably by diffusion/uptake of cytoplasmic GSH into mitochondria. The presence of 1 mM GEE during IVM increased the redox capacity before vitrification and there was no further increase after vitrification/warming. None of the reproducibly detected 1492 spots of 2D DIGE separated proteins were significantly altered by vitrification or GEE supplementation. However, IVM of denuded oocytes significantly affected spindle integrity and chromosome alignment right after warming from vitrification (0 h) in group 1 and spindle integrity in group 2 (P < 0.05). GEE improved recovery in IVM group as numbers of oocytes with unaligned chromosomes and aberrant spindles was not significantly increased compared to unvitrified controls. The supplementation with GEE for 1 h before vitrification also supported more rapid recovery of spindle birefringence. GEE improved significantly development to the 2-cell stage for MII oocytes that were activated directly after vitrification/warming in both experimental groups, and also the blastocyst rate in the IVO GEE-supplemented group compared to the controls (P < 0.05).

LARGE SCALE DATA

None LIMITATIONS, REASONS FOR CAUTION: The studies were carried out in a mouse model, in IVM denuded rather than cumulus-enclosed oocytes, and in activated rather than IVF MII oocytes. Whether the increased GSH-dependent intra-mitochondrial redox capacity also improves male pronuclear formation needs to be studied further experimentally. The influence of GEE supplementation requires also further examination and optimization in human oocytes before it can be considered for clinical ART.

WIDER IMPLICATIONS OF THE FINDINGS

Although GEE supplementation did not alter the proteome at MII, the GSH donor may support cellular homeostasis and redox regulation and, thus, increase developmental competence. While human MII oocyte vitrification is an established procedure, GEE might be particularly beneficial for oocytes that suffer from oxidative stress and reduced redox capacity (e.g. aged oocytes) or possess low GSH due to a reduced supply of GSH from cumulus. It might also be of relevance for immature human oocytes that develop without cumulus to MII in vitro (e.g. in ICSI cycles) for ART.

STUDY FUNDING AND COMPETING INTERESTS

The study has been supported by the German Research Foundation (DFG FOR 1041; EI 199/3-2). There are no conflict of interests.

Oocyte vitrification does not affect early developmental timings after intracytoplasmic sperm injection for women younger than 30 years old

Oocyte vitrification causes a temporary disassembly of the metaphase plate and spindle, which needs time to recover after warming. As a consequence, early post-fertilization events-such as timing of second polar body extrusion-might be altered, with unknown effects on preimplantation development, timing to pronuclear breakdown, and timing of cleavages. The aim of this study was to evaluate if differences exist among these events when comparing embryos obtained from fresh-donated versus vitrified/warmed oocytes from young women. We performed a prospective study with 201 embryos from 100 fresh and 101 vitrified/warmed oocytes that were subsequently fertilized by intracytoplasmic sperm injection. Kaplan-Meier curves of each time period were generated, in which we observed that median developmental times did not differ between embryos from fresh versus vitrified/warmed oocytes among all the metrics assessed. Thus, for young women without fertility problems, no differences exist between the timing of early developmental milestones in embryos derived from fresh or vitrified oocytes, and vitrification does not affect the preimplantation development of the resulting embryos. Mol. Reprod. Dev. 83: 624-629, 2016. © 2016 Wiley Periodicals, Inc.

Morphokinetics analysis of embryos derived from vitrified/warmed oocytes

PURPOSE

Oocyte vitrification is a worldwide used technique that has proved its worth. Although it was shown not to alter oocyte integrity, a recent study concluded that it may affect oocyte embryo development. As the morphology and kinetics of embryos derived from sibling fresh and vitrified oocytes have not been described previously, the present study evaluates cleavage rate, blastomeres size, fragmentation rate, and blastocyst formation in vitrified/warmed oocyte derived embryos (VODE) as compared with sibling fresh oocytes derived embryos (FODE).

METHODS

This investigation included 90 infertility cases displaying large cohort of mature oocytes at pick up, divided into 2 groups after denudation. A part of oocytes underwent ICSI while others were vitrified. Oocyte warming cycles were performed when no pregnancy was achieved using fresh eggs. Zygote to blastocyst development was recorded prospectively in an image database up to day 5.

RESULTS

VODE did not show major difference as compared with FODE in terms of cleavage rate, number of blastomeres, fragmentation rate, and blastomeres size. Furthermore, percentage of morulae at day 4 and blastocysts at day 5 are not affected by oocyte vitrification.

CONCLUSION

Although our results show that embryo development is not altered by oocyte vitrification, offspring follow-up is essential to exclude any adverse developmental effect of the technique.

Female fertility: is it safe to "freeze?"

Objective:

To evaluate the safety and risk of cryopreservation in female fertility preservation.

Data sources:

The data analyzed in this review were the English articles from 1980 to 2013 from journal databases, primarily PubMed and Google scholar. The criteria used in the literature search show as following: (1) human; embryo; cryopreservation/freezing/vitrification, (2) human; oocyte/immature oocyte; cryopreservation/ freezing/vitrification, (3) human; ovarian tissue transplantation; cryopreservation/freezing/vitrification, (4) human; aneuploidy/DNA damage/epigenetic; cryopreservation/freezing/vitrification, and (5) human; fertility preservation; maternal age.

Study selection:

The risk ratios based on survival rate, maturation rate, fertilization rate, cleavage rate, implantation rate, pregnancy rate, and clinical risk rate were acquired from relevant meta-analysis studies. These studies included randomized controlled trials or studies with one of the primary outcome measures covering cryopreservation of human mature oocytes, embryos, and ovarian tissues within the last 7 years (from 2006 to 2013, since the pregnancy rates of oocyte vitrification were significantly increased due to the improved techniques). The data involving immature oocyte cryopreservation obtained from individual studies was also reviewed by the authors.

Results:

Vitrifications of mature oocytes and embryos obtained better clinical outcomes and did not increase the risks of DNA damage, spindle configuration, embryonic aneuploidy, and genomic imprinting as compared with fresh and slow-freezing procedures, respectively.

Conclusions:

Both embryo and oocyte vitrifications are safe applications in female fertility preservation.

l-carnitine supplementation during vitrification of mouse germinal vesicle stage-oocytes and their subsequent in vitro maturation improves meiotic spindle configuration and mitochondrial distribution in metaphase II oocytes

STUDY QUESTION

How does l-carnitine (LC) supplementation during vitrification and in vitro maturation (IVM) of germinal vesicle stage (GV)-oocytes improve the developmental competence of the resultant metaphase II (MII) oocytes?

SUMMARY ANSWER

LC supplementation during both vitrification of GV-oocytes and their subsequent IVM improved nuclear maturation as well as meiotic spindle assembly and mitochondrial distribution in MII oocytes.

WHAT IS KNOWN ALREADY

Vitrification of GV-oocytes results in a lower success rate of blastocyst development compared with non-vitrified oocytes. LC supplementation during both vitrification and IVM of mouse GV-oocytes significantly improves embryonic development after IVF.

STUDY DESIGN, SIZE, DURATION

GV-oocytes were collected from (B6.DBA)F1 and B6 mouse strains and subjected to vitrification and warming with or without 3.72 mM LC supplementation. After IVM with or without LC supplementation, the rate of nuclear maturation and the quality of MII oocytes were evaluated. At least 20 oocytes/group were examined, and each experiment was repeated at least three times. All experiments were conducted during 2013-2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Extrusion of the first polar body in IVM oocytes was observed as an indication of nuclear maturation. Spindle assembly and chromosomal alignment were examined by immunostaining of α-tubulin and nuclear staining with 4,6-diamidino-2-phenylindole (DAPI). Mitochondrial distribution and oxidative activity were measured by staining with Mitotracker Green Fluorescence Mitochondria (Mitotracker Green FM) and chloromethyltetramethylrosamine (Mitotracker Orange CMTMRos), respectively. ATP levels were determined by using the Bioluminescent Somatic Cell Assay Kit.

MAIN RESULTS AND THE ROLE OF CHANCE

LC supplementation during both vitrification and IVM of GV-oocytes significantly increased the proportions of oocytes with normal MII spindles to the levels comparable with those of non-vitrified oocytes in both mouse strains. While vitrification of GV-oocytes lowered the proportions of MII oocytes with peripherally concentrated mitochondrial distribution compared with non-vitrified oocytes, LC supplementation significantly increased the proportion of such oocytes in the (B6.DBA)F1 strain. LC supplementation decreased the proportion of oocytes with mitochondrial aggregates in both vitrified and non-vitrified oocytes in the B6 strain. The oxidative activity of mitochondria was mildly decreased by vitrification and drastically increased by LC supplementation irrespective of vitrification in both mouse strains. No change was found in ATP levels irrespective of vitrification or LC supplementation. Results were considered to be statistically significant at P < 0.05 by either χ(2)- or t-test.

LIMITATIONS, REASONS FOR CAUTION

It remains to be tested whether beneficial effect of LC supplementation during vitrification and IVM of GV-oocytes leads to fetal development and birth of healthy offspring after embryo transfer to surrogate females.

WIDER IMPLICATIONS OF THE FINDINGS

This protocol has the potential to improve the quality of vitrified human oocytes and embryos during assisted reproduction treatment.

STUDY FUNDING/COMPETING INTEREST

Partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and Mitacs Elevate Postdoctoral Fellowship, Canada.

Cryopreservation of embryos and oocytes in human assisted reproduction

Both sperm and embryo cryopreservation have become routine procedures in human assisted reproduction and oocyte cryopreservation is being introduced into clinical practice and is getting more and more widely used. Embryo cryopreservation has decreased the number of fresh embryo transfers and maximized the effectiveness of the IVF cycle. The data shows that women who had transfers of fresh and frozen embryos obtained 8% additional births by using their cryopreserved embryos. Oocyte cryopreservation offers more advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation, and postponing childbirth, and eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In this review, the basic principles, methodology, and practical experiences as well as safety and other aspects concerning slow cooling and ultrarapid cooling (vitrification) of human embryos and oocytes are summarized.

Health outcomes of children born after IVF/ICSI: a review of current expert opinion and literature

The Sixth Evian Annual Reproduction (EVAR) Workshop Group Meeting was held to evaluate the impact of IVF/intracytoplasmic sperm injection on the health of assisted-conception children. Epidemiologists, reproductive endocrinologists, embryologists and geneticists presented data from published literature and ongoing research on the incidence of genetic and epigenetic abnormalities and congenital malformations in assisted-conception versus naturally conceived children to reach a consensus on the reasons for potential differences in outcomes between these two groups. IVF-conceived children have lower birthweights and higher peripheral fat, blood pressure and fasting glucose concentrations than controls. Growth, development and cognitive function in assisted-conception children are similar to controls. The absolute risk of imprinting disorders after assisted reproduction is less than 1%. A direct link between assisted reproduction and health-related outcomes in assisted-conception children could not be established. Women undergoing assisted reproduction are often older, increasing the chances of obtaining abnormal gametes that may cause deviations in outcomes between assisted-conception and naturally conceived children. However, after taking into account these factors, it is not clear to what extent poorer outcomes are due to the assisted reproduction procedures themselves. Large-scale, multicentre, prospective epidemiological studies are needed to investigate this further and to confirm long-term health consequences in assisted-conception children. Assisted reproduction treatment is a general term used to describe methods of achieving pregnancy by artificial means and includes IVF and sperm implantation. The effect of assisted reproduction treatment on the health of children born using these artificial methods is not fully understood. In April 2011, fertility research experts met to give presentations based on research in this area and to look carefully at the evidence for the effects of assisted reproduction treatment on children's health. The purpose of this review was to reach an agreement on whether there are differences in the health of assisted-conception children with naturally conceived children. The researchers discovered no increased risk in birth defects in assisted-conception children compared with naturally conceived children. They found that IVF-conceived children have lower birth weights and higher fat under the skin, higher blood pressure and higher fasting glucose concentrations than naturally conceived children; however, growth, development and cognitive function are similar between groups. A very low risk of disorders of genetic control was observed in assisted-conception children. Overall, there did not appear to be a direct link between assisted reproduction treatment and children's health. The researchers concluded that the cause of some differences in the health of children conceived using assisted reproduction treatment may be due to the age of the woman receiving treatment. Large-scale, research studies are needed to study the long-term health of children conceived using assisted reproduction treatment.

The current challenges to efficient immature oocyte cryopreservation

Oocyte cryopreservation represents an important tool for assisted reproductive technology. It offers the opportunity to preserve fertility in women at risk of loss of the ovarian function for various pathologies. It also represents a treatment alternative for couples that cannot benefit from embryo cryopreservation because of moral, religious, or legal constrains. On the other hand, in vitro oocyte maturation has a range of applications. It can be applied in patients with a contraindication to ovarian stimulation to prevent ovarian hyperstimulation syndrome or to eliminate the risk of stimulation of hormone-sensitive tumours in cancer patients. However, while mature oocyte cryopreservation has found wide-spread application and oocyte in vitro maturation has a place for the treatment of specific clinical conditions, data on the efficiency of freezing of immature or in vitro matured oocytes are poorer. In this review we will focus on the combination of oocyte in vitro maturation with oocyte cryopreservation with particular emphasis on the biological implications of the cryopreservation of immature or in vitro matured oocytes. The two cryopreservation approaches, slow freezing and vitrification, will be discussed in relation to possible cryodamage occurring to subcellular structures of the oocyte and the functional interaction between oocyte and cumulus cells.

Replacement of sodium with choline in slow-cooling media improves human ovarian tissue cryopreservation

Ovarian tissue cryopreservation is a promising technique for fertility preservation in young female cancer patients and efforts have been made to improve its effectiveness. During cooling and thawing, sodium ions significantly contribute to the 'solute effect' that plays a major role in disrupting cell membranes. Choline ions, which do not cross the cell membrane, should not contribute to the intracellular solute load. The present study assessed the effects of sodium substitution with choline in slow-cooling freezing media on human ovarian cortical strip cryopreservation. A total of 629 follicles (fresh control n=266; cryopreserved n=363), collected from ovarian biopsies of 11 women (22-40years) during laparoscopic surgery, were studied by light microscopy, immunohistochemistry and transmission electron microscopy to evaluate their morphology, apoptosis and ultrastructure. The results demonstrate that choline substitution leads to: (i) an improved preservation of oocytes and follicular cells; (ii) the recovery of a higher percentage of grade-1 follicles negative for p53, p21 and Apaf-1 apoptotic markers; (iii) a reduced mitochondrial damage as observed at an ultrastructural level; and (iv) a better preservation of ovarian tissue stroma. In conclusion, the use of choline-based media may represent a valuable tool to improve human ovarian tissue cryopreservation. Ovarian tissue cryopreservation is a promising fertility preservation approach for cancer patients before undergoing treatments that irreversibly reduce the ovarian reserve. Autotransplantation of ovarian cortical strips has resulted in viable offspring in animal models and human. Worldwide, 20 live births have been reported thus far following autotransplantation of frozen-thawed ovarian tissue. However, currently the success rate of this technology is far from being satisfactory. This could be due to inappropriate cryopreservation procedures that might impair the physiology of ovarian follicles. Sodium ions contained in freezing media significantly contribute to the 'solute effect' that plays a major role in disrupting cell membranes. Choline ions, which do not cross the cell membrane, would not be expected to contribute to the intracellular solute load. In the present study we assessed the effects of sodium substitution with choline in slow-cooling freezing media on human ovarian cortical strip cryopreservation. A total of 629 follicles, collected from ovarian biopsies of 11 women (aged 22-40years) during laparoscopic surgery, have been studied by light microscopy, immunohistochemistry and transmission electron microscopy to evaluate their morphology, apoptosis and ultrastructure. Results demonstrated that choline substitution allowed: (i) a better preservation of oocytes and follicular cells; (ii) the recovery of an higher percentage of healthy follicles negative for apoptotic markers; (iii) a lower mitochondria ultrastructural damage; and (iv) a better preservation of ovarian tissue stroma. In conclusion, the use of choline-based media could represent a valuable tool to cryopreserve human ovarian tissue for fertility preservation.

Developmental potential of human oocytes matured in vitro followed by vitrification and activation

Background

Oocyte in vitro maturation (IVM) and cryopreservation at the time of routine ovarian tissue freezing may be offered to cancer patients as an additional option for fertility preservation. This study aimed to investigate the developmental capacity of oocytes isolated from unstimulated ovaries.

Methods

Immature oocytes (n = 63) from seven consenting premenopausal patients were analysed. Oocytes were collected during routine laparoscopic examination with biopsy of an ovary (cystic adnexal mass, n = 3; cervical adenocarcinoma, n = 2) or oophorectomy (sex reassignment surgery, n = 2) without previous stimulation of the ovaries. The stage of the patient’s menstrual cycle was not considered. Oocytes in all visible antral follicles were aspirated from ovaries, cultured in IVM medium and vitrified at the MII stage before being kept in liquid nitrogen for at least one month. After warming, oocytes were subjected to parthenogenetic activation by chemical stimulus. Their further development was recorded at intervals of 24 hours for up to 6 days of culture.

Results

61.9% of oocytes matured in vitro within 48 hours. The survival rate after vitrification and warming was 61.5%. A total of 75% of surviving oocytes were able to respond to artificial activation, 44.4% of the parthenotes developed to early embryonic stage. However, only 1 in 18 (5.6%) of the resulting embryos reached blastocyst stage.

Conclusions

Oocytes matured in vitro from unstimulated ovaries seem to have limited developmental potential after cryopreservation and artificial activation. Although the outcome of IVM for non-stimulated oocytes is poor, it is currently the only chance besides cryopreservation of ovarian tissue for women for whom ovarian stimulation is not possible due to life circumstances. Based on our preliminary results, we suggest that the use of cryopreserved ovaries for fertility preservation in women with cancer warrants further investigation.

Is vitrification of oocytes useful for fertility preservation for age-related fertility decline and in cancer patients?

The aim of this review is to provide current knowledge on oocyte cryopreservation, with special emphasis on vitrification as a means to preserve fertility in different indications. Major advancements achieved in the past few years in the cryolaboratory have facilitated major changes in our practice. Areas such as fertility preservation for social or oncologic reasons, the possibility to create oocyte banks for egg donation programs, the opportunity to avoid ovarian hyperstimulation syndrome, or to accumulate oocytes in low-yield patients, or even to offer treatment segmentation by stimulating the ovaries, vitrifying, and then transferring in a natural cycle are some of the options that are now available with the development of cryopreservation. We present general experience from our group and others on fertility preservation for age-related fertility decline as well as in oncologic patients, confirming that oocyte vitrification is a standardized, simple, reproducible, and efficient option.

Spindle and chromosomal alterations in metaphase II oocytes

The spindle apparatus is a vital structure and must be structurally intact for proper segregation of the oocyte's genetic material during metaphase II. Endometriosis, oxidative stress, and cryopreservation can all adversely affect the structural integrity of the spindle, potentially resulting in aneuploidy and spontaneous abortion of the embryo. Advances in spindle imagery have made it possible to visualize the effects of environmental stresses on spindle structure. Deviation from an oocyte's normal environment can seriously impair the positioning and integrity of the spindle. Oocytes cryopreservation causes depolymerization and repolymerization of the spindle. Oocytes can also be preserved in an immature state for later in vitro maturation. A comprehensive understanding of the spindle behavior is paramount for the effective manipulation of oocytes in an assisted reproductive setting.

Is it best to cryopreserve human cumulus-free immature oocytes before or after in vitro maturation?

Freezing unfertilized oocytes is an option for females without a partner, either to preserve their fertility prior to sterilizing cancer treatment or for social reasons. Our study considered whether it is best to freeze immature human oocytes at the germinal vesicle (GV) stage, prior to in vitro maturation (IVM) or at metaphase-II (M-II), after IVM. Sibling GV-stage oocytes from stimulated ICSI cycles were allocated to freezing either prior to (n=109) or after (n=107) IVM. Cumulus-free oocytes were cryopreserved using a choline-substituted slow-freezing protocol and matured in a defined medium, with analysis of chromatin, microtubules, and microfilaments by three-dimensional imaging. Cryopreserved oocytes were compared with oocytes matured in vitro but never frozen (n=114). Survival was similar between oocytes frozen before or after IVM (69.7% vs. 70.5%). Polar body extrusion after IVM was lower in oocytes frozen at the GV stage versus those matured and then frozen (51.3% vs. 75.7%) or not frozen (75.4%). Stratification by patient age (<36 and ⩾36year) showed no difference in oocyte survival or maturation. Oocytes frozen as GVs showed elevated proportions of spontaneous activation (with or without polar body), an effect augmented by patient age. Spindle and chromosome configurations were disrupted to similar extents in both groups of frozen oocytes, with no further detrimental effect of patient age. The length, width, and volume of bipolar M-II spindles were comparable in all three groups. When frozen as GVs, oocytes exhibited decreased maturation and increased spontaneous activation, suggesting that it is best to freeze oocytes at M-II.

Freezing of oocytes and its effect on the displacement of the meiotic spindle: short communication

Our investigations focused on spindle dynamics/displacement in frozen-thawed human oocytes. In each oocyte, prior to freezing and after thawing and culturing, the presence/location of the spindle was determined with the Polscope technique. A total of 259 oocytes have been thawed with a survival rate of 81.1%. From the 210 survived oocytes, 165 were fertilized (78.6%) and 89.1% of them cleaved. A total of 143 embryos were transferred into 63 patients resulting in 11 clinical pregnancies (17.5%), 7 of which resulted in live birth of 8 babies (1 twin pregnancy). We were able to detect the spindle in 221 of 259 oocytes (85.3%). After thawing and culturing the oocytes, we were able to visualize the spindle in 177 of 210 oocytes (84.3%). In 83 of these 177 oocytes, the spindle was observed to be in the same location as it was before cryopreservation (46.9%). However, in 94 of these 177 oocytes (53.1%), the spindle reformed in a different position/location relative to the polar body. Our results show that after thawing and culture in half of the spindle-positive oocytes the spindle was detected in a new location, indicating that the spindle and the polar body move relative to each other.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Current status of human oocyte and embryo cryopreservation

PURPOSE OF REVIEW

To summarize recent advances in oocyte and embryo cryopreservation techniques and outcomes.

RECENT FINDINGS

Vitrification is gradually replacing slow freezing due to a better survival rate after thawing. Most units use vitrification for both oocyte and blastocyst cryopreservation, as these two biological structures did not perform very well with slow freezing technique. Basic experiments show that cellular damage seems lower after vitrification. Taken all together, this is helping vitirification to be expanding rapidly, and new clinical indications are being incorporated as well (i.e., fertility preservation).

SUMMARY

Cryopreservation has been used as a complement to IVF, and recent publications indicate that pregnancy rates achieved with frozen oocytes and embryos are comparable with those achieved in fresh cycles. Multiple publications studying oocyte and embryo physiology during cryopreservation have been published recently; however, larger studies are needed to verify the efficacy of new cryopreservation techniques. Vitrification is a simple and robust technique that is being incorporated into the majority of IVF units, mainly for oocyte and blastocyst cryopreservation.

Maturation outcomes are improved following Cryoleaf vitrification of immature human oocytes when compared to choline-based slow-freezing

PURPOSE

The cryopreservation of immature oocytes permits oocyte banking for patients at risk of losing their fertility. However, the optimum protocol for such fertility preservation remains uncertain.

METHODS

The present study investigated the survival, maturation, cytoskeletal and chromosome organization of sibling immature oocytes leftover from controlled ovarian stimulation cycles, that were either slow-frozen (with choline-substitution) or vitrified. A comparison group included oocytes that were never cryopreserved.

RESULTS

Among the three groups, comparable rates were observed for both survival (67-70%) and polar body extrusion (59-79%). Significantly more oocytes underwent spontaneous activation after IVM following slow-freezing compared with either vitrification or no cryopreservation. Likewise, the incidence of spindle abnormalities was greatest in the slow-frozen group, with no differences in spindle morphometrics or chromosome organization.

CONCLUSIONS

While the overall incidence of mature oocytes with normal bipolar spindles from warmed immature oocytes was low, the yield using Cryoleaf vitrification was slightly superior to choline-based slow-freezing.

Mouse ovarian follicle cryopreservation using vitrification or slow programmed cooling: assessment of in vitro development, maturation, ultra-structure and meiotic spindle organization

AIM

To compare different outcomes of vitrification and slow freezing of isolated pre-antral follicles and to evaluate different cryo-devices for vitrification of isolated follicles.

METHODS

Pre-antral follicles were isolated from mouse ovaries and cryopreserved using vitrification and slow freezing. A preliminary experiment was carried out to select the optimal cryo-device for vitrification of isolated follicles. A total of 414 follicles were randomly distributed among four groups: control (CT) fresh (n=100), nylon mesh (n=96), electron microscopy grid (n=102), and micro-capillary tips (n=116). Subsequently, a total of 979 follicles were randomly assigned to three different groups: CT fresh (n=256), vitrification (n=399) and slow freezing (n=324). CT and cryopreserved/thawed follicles were cultured in vitro and examined daily for development. Final maturation was triggered with human chorionic gonadotrophin and rates of oocyte maturation were calculated. The ultra-structure of cryopreserved/thawed follicles was studied using electron microscopy. Meiotic spindle presence and organization in mature oocytes were examined using the Oosight imaging system.

RESULTS

  Micro-capillary tips resulted in poor immediate post-warming survival but no differences were observed in the subsequent in vitro development characteristics between different cryo-devices. Nylon mesh proved to be the easiest carrier, particularly when large numbers of follicles were to be vitrified. Compared to vitrification, slow freezing resulted in a significantly lower number of intact follicles at the end of the culture period (P<0.0001). However all other outcome measures were comparable between both techniques.

CONCLUSIONS

Isolated follicles were more vulnerable to cryodamage after slow freezing as compared to vitrification.

Vitrification in open and closed carriers at different cell stages: assessment of embryo survival, development, DNA integrity and stability during vapor phase storage for transport

Background

High cooling rates with vitrification can be achieved through the use of carriers that allow cryopreservation in fluid volumes < one μl. Open carriers allow direct contact of embryos with liquid nitrogen (LN2) whereas closed carrier systems sequester the embryo within a sealed system during immersion in LN2. The use of closed systems may be preferable to reduce the possibility of cross-contamination. In the present study, we compare open and closed carriers for vitrification of embryos. We also examine their ability to retain embryo viability during vapor phase transport.

Methods

Frozen one-cell mouse embryos were thawed and randomly allocated to treatment groups. Embryos were cultured and vitrified at the 8-cell (CL) or at the blastocyst (BL) stage. The cryoloop, an open carrier was tested against two closed systems, the Cryotip and the HSV straw. Carriers were tested for their ability to maintain embryo viability when held in the vapor phase of a dry shipper for a period of 96 hours. Outcome parameters monitored were embryo survival, recovery, subsequent development and signs of DNA damage.

Results

A total of 561 embryos were vitrified. The only parameter significantly affected by the type of carrier was the percentage of embryos recovered after warming. Vitrification of both CL and BL stage embryos in the Cryotip resulted in significantly lower recovery rates (P < 0.001). The subsequent developmental parameters were unaffected by either the carrier or the cell stage. Vapor phase storage for 96 hours under "transport conditions" did not appear to adversely affect the viability after warming. Quantitative analysis for DNA damage showed that <5% of cells were TUNEL positive. Interestingly, the overall percent of cells exhibiting DNA damage was lower after CL stage vitrification (P < 0.001).

Conclusion

This study is one of the first to examine DNA integrity after vitrification on different carriers and at different cell stages. It also provides insight on relative safety of short term vapor storage of vitrified embryos during transport. Within the limits of this study we could not detect an adverse effect of vapor storage on blastomere DNA or other measured outcome parameters.

Slow oocyte freezing and thawing in couples with no sperm or an insufficient number of sperm on the day of in vitro fertilization

BACKGROUND

The clinical results of in vitro fertilization of slowly frozen-thawed oocytes are known to be significantly worse than those obtained by fresh oocytes. Little is known about the factors affecting the clinical outcome of frozen-thawed oocytes. The aim of this retrospective study was to explore the role of oocyte cryopreservation in the group of patients with no available sperm on the day of in vitro fertilization. Additionally, the effects of the female serum FSH level and sperm quality on the clinical outcome of frozen-thawed oocytes were evaluated.

METHODS

Oocytes were slowly frozen and thawed in 22 infertile couples with no sperm or insufficient number of sperm on the day of in vitro fertilization (IVF). In 9 couples with severe azoospermia or oligoasthenoteratozoospermia frozen-thawed oocytes were fertilized by autologous sperm of bad quality when available (Group 1). In 13 couples with non-ejaculation due to psychological stress on the day of classical IVF or severe azoospermia frozen-thawed oocytes were fertilized by autologous or donated sperm of normal quality (Group 2). Oocytes were thawed in 23 cycles and microinjected by the autologous or donated sperm, when available. The clinical outcome of intracytoplasmic sperm injection--ICSI (fertilization, blastocyst, and pregnancy rates) was compared to the outcome of fresh oocytes of the same group of patients; additionally, the female serum FSH level and the sperm quality were compared.

RESULTS

In all couples, 70.5% of oocytes survived the freeze-thaw procedure. After ICSI, 61.5% of thawed oocytes were fertilized. Twenty one% of embryos developed to the blastocyst stage. The pregnancy rates per embryo transfer and freeze-thaw cycle were 33.3% and 17.4%, respectively. All pregnancies ended in the birth of a baby without congenital anomalies. In patients with severe azoospermia or oligoasthenoteratozoospermia there was no statistically significant difference in pregnancy rates per cycle obtained by thawed oocytes vs. fresh oocytes in previous ICSI cycles (14.2% vs. 13.6%) but there was a higher proportion of abnormal, non-cleaved or triploid zygotes when frozen-thawed oocytes were microinjected (33.3% vs. 11.8%; P < 0.01). The female serum FSH levels did not affect the survival and fertilization of frozen-thawed oocytes, but in patients with increased serum FSH level no pregnancies were achieved. After the complete freeze-thaw cycle, there was a significantly higher fertilization rate and tendency to higher pregnancy rates per thawing cycle after the microinjection of autologous or donated sperm of normal quality than autologous sperm of poor quality.

CONCLUSION

The slow oocyte freezing and thawing is a valuable method when no or insufficient number of sperm are available on the day of in vitro fertilization. The quality of sperm is an important factor affecting the clinical outcome achieved by frozen-thawed oocytes.

Current results with slow freezing and vitrification of the human oocyte

The past decade has witnessed renewed interest in human oocyte cryopreservation (OCP). This article reviews the two general methods used for OCP, slow freezing and vitrification, compares the outcomes associated with each technique and discusses the factors that might influence success with OCP (such as oocyte selection or day of transfer). Based on available data, OCP offers a reliable, reproducible method for preservation of the female gamete and will find increasing application in assisted reproductive technology. Oocyte cryopreservation can provide a number of advantages to couples undergoing assisted reproduction or to women interested in fertility preservation. Two methods, slow freezing and vitrification, have been used successfully for oocyte cryopreservation. This article reviews and compares these methods, and discusses various factors that can impact upon success of oocyte cryopreservation.

History of oocyte cryopreservation

The potential advantages of being able to cryopreserve oocytes have been apparent for many decades. Technical difficulties associated with the unique properties of the mammalian oocyte initially retarded rapid development in this area but recent advances have overcome many of the problems. A stage has now been reached where oocyte cryopreservation can be considered an important component of human assisted reproductive technology. The potential advantages of being able to cryopreserve oocytes have been apparent for many decades. Technical difficulties associated with the unique properties of the mammalian oocyte initially retarded rapid development in this area but recent advances have overcome many of the problems. A stage has now been reached where oocyte cryopreservation can be considered an important component of human assisted reproductive technology.

Qualitative and morphometric analysis of the ultrastructure of human oocytes cryopreserved by two alternative slow cooling protocols

PURPOSE

To ascertain possible cell damage from cryopreservation, the ultrastructure of human oocytes cryopreserved by slow cooling was assessed.

MATERIALS AND METHODS

Cryopreservation was performed through two protocols with one-step or two-step propanediol. Fresh control oocytes were examined for comparison. Samples were processed for transmission electron microscopy analysis.

RESULTS

By light microscopy, both fresh and frozen-thawed oocytes appeared regularly rounded, with intact zona pellucida, and homogeneous cytoplasm. By electron microscopy observation, organelles were abundant and uniformly dispersed. Mitochondria-smooth endoplasmic reticulum associations appeared regular. However, both the amount and density of cortical granules appeared abnormally reduced in frozen-thawed samples. Slight to moderate vacuolization was also found in the ooplasm of oocytes of both frozen groups.

CONCLUSIONS

Slow cooling ensures a good overall preservation of human oocytes. However, cytoplasmic vacuolization and cortical granule loss appears associated with cryopreservation, irrespective of the protocol used.

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.

Oocyte cryopreservation: is it time to remove its experimental label?

As more reproductive-age women survive cancer at the expense of gonadotoxic therapy, the need for viable fertility preservation options has become paramount. Embryo cryopreservation, often using donor sperm, has been the standard offered these women over the past 20 years. Preservation of unfertilized oocytes now represents an acceptable and often equally viable alternative, particularly for single women, due to technologic advances made in the past decade. Given such, oocyte cryopreservation's experimental designation and need for IRB approval should thus be revisited.

Live birth from vitrified-warmed human oocytes fertilized with frozen-thawed testicular spermatozoa

A couple with male infertility due to non-obstructive azoospermia were referred to the fertility centre for treatment. Testicular biopsy was performed on the male partner and testicular samples were frozen. The female partner underwent ovarian stimulation and 31 mature oocytes were recovered by ultrasound-guided vaginal aspiration. Twelve oocytes were cryopreserved by the Cryotop vitrification method and 19 oocytes were inseminated by intracytoplasmic sperm injection (ICSI) using frozen-thawed testicular spermatozoa. Nine out of 19 oocytes were fertilized and the resulting embryos were cryopreserved by slow freezing. Four months later, two out of six thawed embryos were transferred, but no pregnancy resulted. One year later, the couple decided to attempt pregnancy using vitrified oocytes and frozen testicular spermatozoa. Six vitrified-warmed oocytes were injected with frozen-thawed testicular spermatozoa and four were fertilized. On the day of transfer, two cleavage stage embryos (4-cell, 2-cell) were obtained. Serum beta-HCG test 14 days after embryo transfer was positive. Hormonal support for the established pregnancy was maintained with oestradiol and progesterone orally until 12 weeks of gestation. A healthy baby boy weighing 3.09 kg was delivered by elective Caesarean section at 38 weeks of gestation. This case report demonstrates that oocyte cryopreservation by the Cryotop vitrification method does not compromise oocyte developmental competence.

Embryo development of fresh 'versus' vitrified metaphase II oocytes after ICSI: a prospective randomized sibling-oocyte study

BACKGROUND

A successful oocyte cryopreservation programme is of utmost importance where a limited number of oocytes can be inseminated per cycle, to overcome legal and ethical issues related to embryo storage, for oocyte donation programmes and for fertility preservation (especially for cancer patients). Vitrification has been recently proposed as an effective procedure for this purpose.

METHODS

In order to validate the effectiveness of oocyte vitrification a non-inferiority trial was started on sibling metaphase II (MII) oocytes. To demonstrate the non-inferiority based on an absolute difference of 17% in the fertilization rate per sibling oocyte, a minimum of 222 oocytes were required. After oocyte denudation, MII oocytes with normal morphology were randomly allocated to fresh ICSI insemination or to vitrification procedure. If pregnancy was not obtained a subsequent ICSI cycle was performed with warmed oocytes of the same cohort. In both groups, three oocytes were inseminated per cycle by ICSI procedure. Primary end-points were fertilization rates calculated per warmed and per injected oocytes. Secondary end-points were zygote and embryo morphology.

RESULTS

A total of 244 oocytes were involved in this study. Of the 120 fresh sibling oocytes inseminated, 100 were fertilized (83.3%). Survival rate of sibling vitrified oocytes was 96.8% (120/124 oocytes). Fertilization rate after ICSI was 76.6% (95/124) per warmed oocyte and 79.2% (95/120) per survived/inseminated oocyte. No statistical difference in fertilization rates was observed between the two groups when calculated per sibling oocytes (absolute difference -6.73%; OR: 0.65; 95% CI = 0.33-1.29; P = 0.20) and per inseminated oocyte (absolute difference -4.17%; OR: 0.76; 95% CI = 0.37-1.53; P = 0.50). Embryo development was also similar in both treatment groups up till Day 2. The percentage of excellent quality embryos was 52.0% (52/100) in the fresh group and 51.6% (49/95) in the vitrification group (absolute difference -0.43%; OR: 0.98; 95% CI = 0.53-1.79; P = 0.9). The mean age of the 40 patients included in this study was 35.5 +/- 4.8 years (range 26-42). Fifteen clinical pregnancies were obtained in the vitrification cycles of 39 embryo transfers performed (37.5% per cycle, 38.5% per embryo transfer), with an implantation rate of 20.2% (19/94). Three spontaneous miscarriages occurred (20%). Twelve pregnancies are ongoing (30.0% per cycle, 30.8% per embryo transfer) beyond 12 weeks of gestation.

CONCLUSIONS

Our results indicate that oocyte vitrification procedure followed by ICSI is not inferior to fresh insemination procedure, with regard to fertilization and embryo developmental rates. Moreover, ongoing clinical pregnancy is compatible with this procedure, even with a restricted number of oocytes available for insemination. The promising clinical results obtained, in a population of infertile patients, need to be confirmed on a larger scale.

CLINICAL TRIALS REGISTRATION NUMBER

iSRCTN60158641.