Pregnancy and delivery of healthy infants developed from vitrified oocytes in a stimulated in vitro fertilization-embryo transfer program

Fatty acid supplementation into warming solutions improves pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfers

Purpose

This study aimed to examine the embryonic development of human 4-cell stage embryos after warming with fatty acids (FAs) and to assess the pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfers (SVCTs).

Methods

Experimental study: A total of 217 discarded, vitrified human 4-cell stage embryos donated for research by consenting couples were used. The embryos were warmed using the fatty acid (FA)-supplemented solutions (FA group) or nonsupplemented solutions (control group). The developmental rate, morphokinetics, and outgrowth competence were analyzed. Clinical study: The treatment records of women undergoing SVCT in natural cycles between April and September 2022 were retrospectively analyzed (April-June 2022, control group; July-September 2022, FA group).

Results

Experimental study: The rate of morphologically good blastocysts was significantly higher in the FA group than in the control group (p = 0.0302). The morphokinetics during cleavage, morula, and blastocyst stages were comparable between the groups. The outgrowth was significantly increased in the FA group (p = 0.0438). Clinical study: The rates of implantation, clinical pregnancy, and ongoing pregnancy after SVCTs were significantly increased in the FA group (p = 0.0223-0.0281).

Conclusions

Fatty acid-supplemented warming solutions effectively improve embryo development to the blastocyst stage and pregnancy outcomes after SVCTs.

Diamour®, a newly vitrification device for human blastocysts, provides the same efficient perinatal outcomes as the commonly used Cryotop®

OBJECTIVE

The purpose of this study was to investigate the effectiveness of Diamour®, a newly developed vitrification device, for the ultra-rapid frozen storage of human blastocysts.

MATERIALS AND METHODS

Surplus blastocysts obtained using assisted reproductive technology at our clinic during a 2-year period (2018-2019) were assigned for vitrification with the Diamour® device in 2019 or a comparator device in 2018. We retrospectively compared outcomes (clinical pregnancy rate, abortion rate, live birth rate, and perinatal outcomes) between the two vitrification devices.

RESULTS

We obtained 228 blastocysts from 178 patients, and 118 blastocysts were cryopreserved using the Diamour® vitrification device and the other 110 were cryopreserved using a Cryotop®, the comparator device. We found no significant difference between the Diamour®-vitrified and comparator-vitrified blastocysts in clinical pregnancy rate (32.2% vs. 30.9%; p = 0.83), abortion rate (17.0% vs. 9.1%; p = 0.08), and live birth rate (25.4% vs. 26.4%; p = 0.87). The Diamour®-vitrified blastocysts yielded 30 live births, and the comparator-vitrified blastocysts 29. The two devices yielded no significant difference in birth weight (Diamour®: 3049 ± 337 g, comparator: 3008 ± 340 g; p = 0.65) and congenital abnormalities, with just 1 case (cleft lip) noted with Diamour® vitrification (p = 0.33). The devices also showed no significant differences in the incidence of gestational diabetes mellitus, hypertensive disorders of pregnancy, placenta previa, preterm birth, macrosomia, low birth weight, and delivery method.

CONCLUSION

The Diamour® device achieves outcomes similar to those of the currently widely used Cryotop® device for clinical pregnancy with frozen-thawed human blastocysts.

The effects of vitrification on oocyte quality

Vitrification, is an ultra-rapid, manual cooling process that produces glass-like (ice crystal free) solidification. Water is prevented from forming intercellular and intracellular ice crystals during cooling as a result of oocyte dehydration and the use of highly concentrated cryoprotectant. Though oocytes can be cryopreserved without ice crystal formation through vitrification, it is still not clear whether the process of vitrification causes any negative impact (temperature change/chilling effect, osmotic stress, cryoprotectant toxicity, and/or phase transitions) on oocyte quality that translate to diminished embryo developmental potential or subsequent clinical outcomes. In this review, we attempt to assess the technique's potential effects and the consequence of these effects on outcomes.

Vitrification: A Simple and Successful Method for Cryostorage of Human Blastocysts

Cryopreservation is one of the keystones in clinical infertility treatment. Especially vitrification has become a well-established and widely used routine procedure that allows important expansion of therapeutic strategies when IVF is used to treat infertility. Vitrification of human blastocysts allows us to maximize the potential for conception from any one in vitro fertilization cycle and prevents wastage of embryos. This goes even further toward to best utilize a patient's supernumerary oocytes after retrieval, maximizing the use of embryos from a single stimulation cycle. The technology can even be used to eliminate fresh embryo transfers for reasons of convenience, uterine receptivity, fertility preservation, preimplantation genetic diagnosis, or emergency management. In this chapter, the application of vitrification technology for cryopreserving human blastocyst will be revealed through step-by-step protocols. The results that are presented using the described protocols underscore the robustness of the vitrification technology for embryo cryopreservation.

Cryopreservation of Mammalian Oocytes: Slow Cooling and Vitrification as Successful Methods for Cryogenic Storage

Two basic methods for the laboratory-focused cryopreservation of mammalian oocytes are described, based on work with murine oocytes. One method uses a relatively low concentration of the cryoprotectant propanediol plus sucrose and requires controlled rate cooling equipment to achieve a slow cooling rate. This method has also produced live births from cryopreserved human oocytes. The second method, which is described here, employs a high concentration of the cryoprotectant dimethyl sulfoxide plus a low concentration of polyethylene glycol. This is a vitrification method, which involves ultra-rapid cooling by plunging standard straws into liquid nitrogen vapor, hence avoiding the need for specialized equipment, but requires technical ability to manipulate the oocytes quickly in the highly concentrated cryoprotectant solutions. Murine oocytes that have been vitrified using this technique have resulted in live births. Vitrification using other cryoprotectant mixtures is now a popular clinically accepted method for cryobanking of human oocytes.

Equivalent clinical outcome after vitrified-thawed blastocyst transfer using semi-automated embryo vitrification system compared with manual vitrification method

PURPOSE

This study compared Gavi®, an automated system for the equilibration and dehydration steps of vitrification, and a manual vitrification procedure in terms of effects on clinical outcomes.

METHODS

The authors retrospectively compared survival rate, and clinical and perinatal outcomes after vitrified-thawed single blastocyst transfer between Gavi® (G method) in 398 cases and Cryotop® (C method) in 208 cases.

RESULTS

With C and G methods, survival rates were 98.6% (208/211) and 99.3% (398/401), total pregnancy rates were 34.3% (72/208) and 33.4% (133/398), and total miscarriage rates were 22.2% (16/72) and 24.8% (33/133), respectively. Among women <35 years old, pregnancy rates were 41.1% (30/73) and 40.5% (62/153) and miscarriage rates were 13.3% (4/30) and 16.1% (10/62) with C and G methods, respectively. Among women ≥35 years old, pregnancy rates were 31.1% (42/135) and 29.0% (71/245) and miscarriage rates were 28.6% (12/42) and 32.4% (23/71) with C and G methods, respectively. C and G methods showed no significant differences in any trials, including gestational age, cesarean section rate, or birthweight (P > .05 each).

CONCLUSIONS

Gavi® showed comparable clinical outcomes to the manual vitrification method and can be considered an alternative vitrification procedure in assisted reproductive technology.

Chapter 11 Human Embryo Vitrification

Cryopreservation is one of the keystones in clinical infertility treatment. In particular vitrification has become a well-established and widely used routine procedure that has allowed important expansion of therapeutic strategies when IVF is used to treat infertility. Vitrification of human blastocysts allows us to maximize the potential for conception from any single in vitro fertilization cycle and prevents wastage of embryos. The technology may even be used to eliminate fresh embryo transfers for reasons of convenience, uterine receptivity, fertility preservation, preimplantation genetic diagnosis, or emergency management. In this chapter, the application of vitrification technology for cryopreserving human blastocysts will be revealed through step-by-step protocols. The results that are presented using the described protocols underscore the robustness of the vitrification technology for embryo cryopreservation.

Chapter 1 Historical Background on Gamete and Embryo Cryopreservation

This chapter describes the development of the science of cryopreservation of gametes and embryos of various species including human. It attempts to record in brief the main contributions of workers in their attempts to cryopreserve gametes and embryos. The initial difficulties faced and subsequent developments and triumphs leading to present-day state of the art are given in a concise manner. The main players and their contributions are mentioned and the authors' aim is to do justice to them. This work also attempts to ensure that credit is correctly attributed for significant advances in gamete and embryo cryopreservation. In general this chapter has tried to describe the historical development of the science of cryopreservation of gametes and embryos as accurately as possible without bias or partiality.

Comparative efficiency study of fresh and vitrified oocytes in egg donation programs for different controlled ovarian stimulation protocols

The aim of this study was to compare the efficacy when using vitrified and fresh eggs depending on the applied controlled ovarian stimulation protocols in egg donation programs. Study results showed that the controlled ovarian stimulation protocol does not affect the outcome of IVF/ICSI. Vitrification provided survival and pregnancy rates similar to the fresh donor oocyte ones.

A live birth from vitrified-warmed oocytes in a Philadelphia chromosome-positive acute lymphoid leukemia patient 5 years following allogenic bone marrow transplantation and after a magnitude 9.0 earthquake in Japan

Purpose

To report a live birth from vitrified-warmed oocytes for a Philadelphia chromosome-positive acute lymphoid leukemia (Ph-ALL) patient.

Methods

A 20-year-old single woman with Ph-ALL requested oocyte cryopreservation at a private fertility clinic using assisted reproduction technology (ART). In cases of leukemia, there is a very short time before chemotherapy, follwed shortly by total body irradiation (TBI), and although she had already received the chemotherapy, ten oocytes were vitrified and stored for 59 months before warming. Soon after the oocyte cryopreservation, she received TBI and bone marrow transplant (BMT). During the storage, a magnitude 9.0 earthquake occurred making oocyte transport necessary. The embryo transfer was planned in a hormone replacement cycle, and intracytoplasmic sperm injection (ICSI) was performed on the vitrified-warmed oocytes. On day 3, two embryos were transferred.

Results

The patient became pregnant and delivered a healthy girl after ICSI using vitrified-warmed oocytes.

Conclusions

Oocyte cryopreservation is the best option for fertility preservation of young single women with leukemia. Oncologists and gynecologists who conduct ART should cooperate to improve the quality of life of cancer patients.

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.

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.

Oocyte cryostorage to preserve fertility in oncological patients

Thanks to the progress in oncostatic treatments, young women affected by cancer have a fairly good chance of surviving the disease and leading a normal post-cancer life. Quite often, however, polychemiotherapy and/or radiotherapy can induce ovarian damage and significantly reduce the content of follicles and oocytes inside the ovary, thus predisposing the patient to menstrual disorders, infertility, and precocious menopause. Several techniques have been proposed to preserve fertility in these patients; among them oocyte collection and cryopreservation prior to the oncostatic treatment has been widely applied in the last decade. The proper indications, the permitting conditions, the available hormonal stimulation protocols, as well as the effectiveness and limits of this option will be discussed herein, with a comprehensive and up-to-date review of the two techniques commonly used to cryostore oocytes, the slow-freezing technique and the vitrification technique.

First successful birth of twins in India following the transfer of vitrified oocytes

We report the first twin pregnancy and birth in India after the transfer of embryos generated from vitrified and thawed oocytes to a 41-year-old woman who was in a donor program. Embryos were generated from the microinjection of pre-prepared sperms into vitrified oocytes. Twin male babies weighing 750 and 860 g were born by emergency cesarean section. Vitrification is one of the most promising options in cryopreservation and preservation of embryos and 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.

Cryopreservation of Mammalian oocyte for conservation of animal genetics

The preservation of the female portion of livestock genetics has become an international priority; however, in situ conservation strategies are extremely expensive. Therefore, efforts are increasingly focusing on the development of a reliable cryopreservation method for oocytes, in order to establish ova banks. Slow freezing, a common method for cryopreservation of oocytes, causes osmotic shock (solution effect) and intracellular ice crystallization leading to cell damage. Vitrification is an alternative method for cryopreservation in which cells are exposed to a higher concentration of cryoprotectants and frozen with an ultra rapid freezing velocity, resulting in an ice crystal free, solid glass-like structure. Presently, vitrification is a popular method for cryopreservation of embryos. However, vitrification of oocytes is still challenging due to their complex structure and sensitivity to chilling.

Cryopreservation of mammalian oocytes by using sugars: Intra- and extracellular raffinose with small amounts of dimethylsulfoxide yields high cryosurvival, fertilization, and development rates

Accumulation of intra- and extracellular sugars such as trehalose, glucose, and raffinose is central to survival strategies of a variety of organisms coping with extreme conditions including freezing and almost complete drying. The objective of the present study was to investigate the potential application of intra- and extracellular raffinose in combination with low concentrations of dimethylsulfoxide (Me(2)SO) to mammalian oocyte cryopreservation. To this end, the fertilization and embryonic development of cryopreserved metaphase II (M II) mouse oocytes were studied in comparison to unfrozen controls. For cryopreservation, M II oocytes were microinjected with 0.1M raffinose, and then cooled to -196 degrees C in the presence of either 0.3M raffinose and 0.5M Me(2)SO (cryopreservation group 1) or 0.3M raffinose and 1.0M Me(2)SO (cryopreservation group 2). The control groups included untreated oocytes (untreated control) and oocytes microinjected with raffinose, but not frozen (injection control). The post-thaw survival rates were 83.9% and 80.6% for the cryopreservation group 1 and 2, respectively. The fertilization and blastocyst rates in the cryopreservation group 1 (90.0% and 77.8%, respectively) and 2 (94.6% and 72.5%, respectively) were also high and similar to the ones of the injection controls (97.8% and 78.5%, respectively) and untreated controls (98.8% and 83.6%, respectively). These results are consistent with the findings of our earlier studies and support the use of sugars as intra- and extracellular cryoprotectants. Furthermore, the results of the present study indicate that the presence of intra- and extracellular sugars alleviates high concentrations of conventional penetrating cryoprotectants, and thus minimizes their toxicity.

The future potential of cryopreservation for assisted reproduction

Cryopreservation of human gonadal tissue and oocytes has brought about new and exciting research in reproductive medicine, as well as new cryopreservation techniques that are dramatically improving post-thaw viability and freezing damage. The work done on gonadal tissues is aimed at improving the quality of life for infertile patients and for prepubertal patients undergoing gonadotoxic chemotherapy, patients for whom hormonal stimulation/IVF is not an option, and women without partners. Cryopreservation of mature oocytes is the best model for timing IVF. Vitrification is likely to benefit the field, and since 2005, implantation and pregnancy rates from vitrified oocytes have matched or eclipsed results from conventional methods, due to new cell-specific methods and formulas. Cryopreservation of immature oocytes leads to a new direction of egg banking in future. Preserving ovarian tissue for autografting is still promising and has resulted in folliculogenesis, resumed hormone production and live births in limited cases. The use of small cortical blocks, or mechanical/chemical digestion of ovarian tissue for isolation of follicles is a new direction for ovary preservation for reasons of cryoprotectant permeation and graft revascularization. Maturation of follicles in vitro has become more feasible with the use of alginate microencapsulation. Testicular tissue preservation has taken a sharp turn towards preservation of gonadal stem cells. Research into the mechanism for spermatogenesis points to the ability for male germ cells to resume spermatogenesis. The cryopreservation of minced testicular tissue for isolation of germ cells via chemical digestion has produced viable cells, however, structural damage that may be avoided by vitrification has been noted to the surrounding cell junctions and supporting cells.

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.

Human oocyte cryopreservation: comparison between slow and ultrarapid methods

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

Several aspects of animal embryo cryopreservation: anti-freeze protein (AFP) as a potential cryoprotectant

With the development of embryo technologies, such as in vitro fertilization, cloning and transgenesis, cryopreservation of mammalian gametes and embryos has acquired a particular interest. Despite a certain success, various cryopreservation techniques often cause significant morphological and biochemical alterations, which lead to the disruption of cell organelles, cytoskeleton damages, cell death and loss of embryo viability. Ultrastructural studies confirm high sensitivity of the cell membrane and organelle membrane to freezing and thawing. It was found that many substances with low molecular weights have a protective action against cold-induced damage. In this concern, an anti-freeze protein (AFP) and anti-freeze glycoproteins (AFGPs), which occur at extremely high concentrations in fish that live in Arctic waters and protect them against freezing, may be of potential interest for cryostorage of animal embryos at ultra-low temperatures. This mini-review briefly describes several models of AFP/AFGP action to preserve cells against chilling-induced damages and indicates several ways to improve post-thaw developmental potential of the embryo.

Application of intra- and extracellular sugars and dimethylsulfoxide to human oocyte cryopreservation

PURPOSE

Oocyte cryopreservation may avoid many complications of human embryo freezing and provide future fertility for women undergoing cancer therapy. The objective of this study was to explore the application of intra- and extracellular sugars in combination with small amounts of dimethylsulfoxide (DMSO) to human oocyte cryopreservation as an alternative approach.

METHODS

Discarded human oocytes that were obtained from IVF patients under informed consent and IRB approval, were cryopreserved by slow cooling to -196 degrees C after being randomly distributed into three groups: (i) DMSO control without intra- and extracellular sugar; (ii) extracellular sugar (raffinose) + DMSO; and (iii) intra- and extracellular sugar (trehalose and raffinose, respectively) + DMSO. Subsequently, all cryopreserved oocytes were thawed rapidly, and their survival was assessed by morphological criteria after 24 h of culture.

RESULTS

A total of 71 oocytes were evaluated in three groups with survival rates of 88.5% (23/26), 68.2% (15/22), and 52.2% (12/23) for intra- and extracellular sugar+DMSO, extracellular sugar+DMSO, and DMSO control groups, respectively.

CONCLUSION

These results support the use of intra- and extracellular sugars as an alternative approach for cryopreservation of human oocytes.

Permeability of the rhesus monkey oocyte membrane to water and common cryoprotectants

Successful cryopreservation of oocytes of the rhesus monkey (Macaca mulatta) would facilitate the use of this valuable animal model in research on reproduction and development, while providing a stepping stone towards human oocyte cryopreservation and the conservation of endangered primate species. To enable rational design of cryopreservation techniques for rhesus monkey oocytes, we have determined their osmotic and permeability characteristics in the presence of dimethylsulfoxide (DMSO), ethylene glycol (EG), and propylene glycol (PROH), three widely used cryoprotectants. Using nonlinear regression to fit a membrane transport model to measurements of dynamic cell volume changes, we estimated the hydraulic conductivity (L(p)) and cryoprotectant permeability (P(s)) of mature and immature oocytes at 23.5 degrees C. Mature oocyte membranes were most permeable to PROH (P(s) = 0.56 +/- 0.05 microm/sec) and least permeable to DMSO (P(s) = 0.24 +/- 0.02 microm/sec); the permeability to EG was 0.34 +/- 0.07 microm/sec. In the absence of penetrating cryoprotectants, mature oocytes had L(p) = 0.55 +/- 0.05 microm/min/atm, whereas the hydraulic conductivity increased to 1.01 +/- 0.10, 0.61 +/- 0.07, or 0.86 +/- 0.06 microm/min/atm when mature oocytes were exposed to DMSO, EG, or PROH, respectively. The osmotically inactive volume (V(b)) in mature oocytes was 19.7 +/- 2.4% of the isotonic cell volume. The only statistically significant difference between mature and immature oocytes was a larger hydraulic conductivity in immature oocytes that were exposed to DMSO. The biophysical parameters measured in this study were used to demonstrate the design of cryoprotectant loading and dilution protocols by computer-aided optimization.

Stem cells and female reproduction

Several recent findings in stem cell biology have resulted in new opportunities for the treatment of reproductive disease. Endometrial regeneration can be driven by bone marrow derived stem cells. This finding has potential implications for the treatment of uterine disorders. It also supports a new theory for the etiology of endometriosis. The ovaries have been shown to contain stem cells that form oocytes in adults and can be cultured in vitro to develop mature oocytes. Stem cells from the fetus have been demonstrated to lead to microchimerism in the mother and implicated in several maternal diseases. Additionally the placenta may be another source of hematopoietic stem cell. Finally endometrial derived stem cells have been demonstrated to differentiate into non-reproductive tissues. While we are just beginning to understand stem cells and many key questions remain, the potential advantages of stem cells in reproductive biology and medicine are apparent.

Oocyte cryopreservation

Over the last few years, there has been renewed interest and scientific debate concerning human oocyte cryopreservation. The aim of this study was to analyse the clinical data coming from our long experience of slow-freezing oocytes. Between 2001 and 2007, 1280 thawing cycles were carried out using oocytes previously frozen by means of a slow 1,2 propaniedol+sucrose protocol. A total of 7585 oocytes were thawed, of which 4409 survived and 3622 were microinjected; 144 clinical pregnancies were obtained. The number of thawing cycles increased from 19 in 2001 to 268 in 2007, and the number of thawed oocytes from 197 to 1652. Although the survival rate was significantly lower in the period 2002-2005 than in the period 2006-2007, pregnancy and implantation rates steadily improved from respectively 6.7% and 2.4% in 2001 to 15% and 8.2% in 2007. Our data demonstrate a clinically important improvement in oocyte crypreservation over the years in a Centres with proved experience, and can be offered as a standard of care not only before cancer treatment but also for couples refusing embryo crypreservation or in countries with very restrictive limitations on embryo or zygote freezing.