Clinical outcomes resulting from the transfer of vitrified human embryos using a new device for cryopreservation (plastic blade)

Hyaluronan-enriched transfer medium (HETM) can improve the implantation rate in morphologically poor euploid blastocyst transfer

PURPOSE

Hyaluronan-enriched transfer medium (HETM) could improve the clinical pregnancy rate (CPR) for patients with repeated implantation failures (RIF). In contrast, there have been seldom reports addressing the potentially beneficial effects of HETM for morphologically poor blastocysts (MPBLs). Our study aimed to evaluate whether the use of HETM would improve the CPR for the patients who were transferred with euploid MPBLs.

METHODS

Patients who underwent single euploid blastocyst transfer between July 2020 and June 2022 were enrolled. We included only those blastocysts confirmed as euploid by PGT-A, and those blastocysts were transferred after thawing. The natural ovulatory cycle or hormone replacement cycle (HRC) protocol were used for endometrial preparation for frozen embryo transfer (FET). A total of 1,168 FET cycles were performed in the study period, including 954 cycles of morphologically good blastocysts (≥ 4BB in Gardner's classification), and 85 cycles of MPBLs, of which 47 were transferred using HETM in FET (the HETM group), and the remaining 38 were transferred with the medium without hyaluronan (the control group). We compared the CPR between these two groups.

RESULTS

The characteristics of patients were similar between the HETM and control groups. The CPR in the HETM group was significantly higher than the control group (47.4% and 21.5%, respectively, p = 0.019). The multiple logistic regression analysis found that the use of HETM was a predictive factor of positive pregnancy outcomes (OR = 5.08, 95% CI = 1.62-16.0, p = 0.019).

CONCLUSION

Our data suggests that HETM used in the euploid blastocyst transfer can improve the clinical pregnancy rates of morphologically poor blastocysts.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Increasing number of implantation failures and pregnancy losses associated with elevated Th1/Th2 cell ratio

PROBLEM

We aimed to assess whether an imbalance of T-helper (Th) 1 and Th2 cells contributes to implantation failure and pregnancy loss.

METHOD OF STUDY

In this cross-sectional study, 197 consecutive patients with a history of repeated implantation failure (RIF) after three or more embryo transfer (ET) cycles and/or recurrent pregnancy loss (RPL) after two or more clinical pregnancy losses underwent Th cell testing. After excluding 42 women aged ≥44 and 9 with vitamin D supplementation, we recruited 146 women including 79 with RIF and 81 with RPL. Fourteen women had a history of both RIF and RPL. We also recruited 45 fertile women and 40 general infertile women without a history of in vitro fertilization treatment. This study was approved by the local ethics committee.

RESULTS

There was no significant difference in IFN-γ-producing Th1 and IL-4-producing Th2 cell levels between the fertile and general infertile women, but Th1 cell levels and the Th1/Th2 cell ratio were significantly higher in the women with ≥4 ET cycles and ≥2 pregnancy losses than in the fertile and general infertile women. In the general infertile women, the total livebirth rates including natural conception after two ET cycles in the normal and high Th1/Th2 groups (Th1/Th2 <11.8 and ≥11.8, respectively) were 66.7% and 87.5%, respectively (p = .395).

CONCLUSIONS

A high Th1/Th2 cell ratio was linked to ≥4 implantation failure cycles and ≥2 pregnancy losses but not to general infertility.

Impact of chronic endometritis on endometrial receptivity analysis results and pregnancy outcomes

BACKGROUND

The aim of this study is to evaluate the relationship between chronic endometritis (CE) and a personalized window of implantation (WOI), identified by results of endometrial receptivity analysis (ERA), and pregnancy outcomes following embryo transfer (ET) based on the ERA outcomes.

METHODS

The single-center, cross-sectional study was designed. The study population consisted of 101 infertile women who underwent endometrial sampling between June 2018 and February 2020. We recruited 88 patients who underwent ERA testing and immunohistochemistry of the plasma cell marker CD138 to diagnose CE within 3 months of testing. Subjects were divided into three groups as follows: 33 without CE (non-CE group); 19 with untreated CE at ERA testing (CE group); and 36 successfully treated for CE before ERA testing (cured-CE group). CE diagnosis was defined as ≥5 CD138-positive plasma cells per 10 random stromal areas at ×400 magnification.

RESULTS

In non-CE, CE, and cured-CE groups, the numbers of CD138-positive cells were 0.7 ± 1.0, 28.5 ± 30.4, and 1.3 ± 1.3, respectively (p < .001). The rates of "receptive" endometrium in non-CE and cured-CE groups were 57.6% (19 women) and 50.0% (18 women), respectively; however, in the CE group, this rate was significantly lower than the other two groups (p = .009) at only 15.8% (3 women). After CE were treated prior or posterior to the ERA test in cured-CE or CE groups, the clinical pregnancy rates at the first ET in non-CE, CE, and cured-CE groups were 77.8% (21/27 cycles), 22.2% (4/18 cycles), and 51.7% (15/29 cycles), respectively (p < 0.001).

CONCLUSION

CE had detrimental effects on the individual WOI, leading to embryo-endometrial asynchrony; therefore, diagnosis and treatment of CE should be done before ERA testing.

Review of non-permeating cryoprotectants as supplements for vitrification of mammalian tissues

Vitrification of mammalian tissues is important in the areas of human assisted reproduction, animal reproduction, and regenerative medicine. Non-permeating cryoprotectants (CPAs), particularly sucrose, are increasingly used in conjunction with permeating CPAs for vitrification of mammalian tissues. Combining non-permeating and permeating CPAs was found to further improve post-thaw viability and functionalities of vitrified mammalian tissues, showing the potential applications of such tissues in various clinical and veterinary settings. With the rising demand for the use of non-permeating CPAs in vitrification of mammalian tissues, there is a strong need for a timely and comprehensive review on the supplemental effects of non-permeating CPAs toward vitrification outcomes of mammalian tissues. In this review, we first discuss the roles of non-permeating CPAs including sugars and high molecular weight polymers in vitrification. We then summarize the supplemental effects of non-permeating CPAs on viability and functionalities of mammalian embryos, and ovarian, testicular, articular cartilage, tracheal, and kidney tissues following vitrification. Lastly, challenges associated with the use of non-permeating CPAs in vitrification of mammalian tissues are briefly discussed.

Improved outcomes after blastocyst-stage frozen-thawed embryo transfers compared with cleavage stage: a Society for Assisted Reproductive Technologies Clinical Outcomes Reporting System study

OBJECTIVE

To investigate whether there is a difference in obstetrical and perinatal outcomes in blastocyst frozen-thawed embryo transfers (FETs) compared with cleavage-stage FET.

DESIGN

A retrospective cohort study.

SETTING

Not applicable.

PATIENT(S)

Women undergoing autologous FETs at either the blastocyst stage (n = 118,572) or the cleavage stage (n = 117,619) reported to the Society for Assisted Reproductive Technology in the years 2004-2013.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Live birth, gestational age, birth weight, miscarriage.

RESULT(S)

After controlling for confounders, there were a 49% increased odds of live birth after blastocyst-stage FET compared with cleavage-stage FET (odds ratio [OR] = 1.49; 95% confidence interval [CI], 1.44, 1.54). Additionally, blastocyst FET was associated with a 68% (OR = 1.68; 95% CI, 1.63, 1.74) increased odds of clinical pregnancy and an 7% (OR = 0.93; 95% CI, 0.88, 0.92) decreased odds of miscarriage. There was also a 16% increased odds of preterm delivery (OR = 1.16; 95% CI, 1.06, 1.27) after blastocyst FET but no difference in birth weights.

CONCLUSION(S)

In patients undergoing FET, blastocyst-stage transfer is associated with higher live-birth rates when compared with cleavage-stage transfers. Furthermore, perinatal outcomes are similar between the groups.

Comparison of pregnancy outcomes after vitrification at the cleavage and blastocyst stage: a meta-analysis

OBJECTIVE

This systematic review sought to evaluate the clinical outcomes of vitrification at the cleavage stage and blastocyst stage for embryo transfer in patients undergoing assisted reproductive technology (ART) treatment.

METHODS

We searched for related comparative studies published in the PubMed, EMBASE, and Cochrane Library databases up to July 2017. The primary outcomes were clinical pregnancy rate (CPR) and embryo implantation rate (IR). Secondary outcomes were multiple pregnancy rate (MPR), miscarriage rate (MR), live birth rate (LBR), and ongoing pregnancy rate (OPR). The Mantel-Haenszel fixed effects model and random effects model were used to analyze the summary risks ratios (RRs) with 95% confidence intervals (CIs).

RESULTS

Eight studies with more than 6590 cycles were included in our meta-analysis. Seven studies were observational retrospective comparative studies. One was a prospective study. Overall, the current study summarizes information from 6590 vitrification warming cycles (cleavage stage n = 4594; blastocysts n = 1996). There was no difference in the primary outcome clinical pregnancy rate (RR = 0.97, 95% CI = 0.90-1.04; fixed effects model; I ²  = 21%), whereas vitrified blastocyst transfer was significantly superior to vitrified cleavage-stage embryo transfer regarding the implantation rate (RR = 0.85, 95% CI = 0.74-0.97; random effects model; I ²  = 43). Regarding the secondary outcomes, no differences were found in the multiple pregnancy rate (RR = 1.20, 95% CI = 0.79-1.82; fixed effects model; I ²  = 22), live birth rate (RR = 1.07, 95% CI = 0.98-1.16; fixed effects model; I ²  = 0), and ongoing pregnancy rate (RR = 1.01, 95% CI = 0.92-1.120; fixed effects model; I ²  = 0), whereas a higher miscarriage rate was observed with vitrified blastocyst transfer (RR = 0.65, 95% CI = 0.45-0.93; random effects model; I ²  = 23).

CONCLUSION

In summary, this meta-analysis shows that vitrification at any stage has no detrimental effect on clinical outcome. Blastocyst transfer will still remain a favorable and promising option in ART. Due to the small sample evaluated in the pool of included studies, large-scale, prospective, and randomized controlled trials are required to determine if these small effects are clinically relevant.

Immunosuppressive treatment using tacrolimus promotes pregnancy outcome in infertile women with repeated implantation failures

PROBLEM

We aim to investigate whether the peripheral blood T helper (Th) 1 cell level could predict pregnancy outcome in patients who have experienced repeated implantation failure (RIF, three or more) after ART cycles.

METHOD OF STUDY

This is a prospective cohort study of total 124 women with RIF who showed elevated Th1/Th2 (CD4⁺ IFN-γ⁺ /CD4⁺ IL-4⁺ ) cell ratios (≥10.3) and received tacrolimus at Sugiyama Clinic between November 2011 and July 2016. Patients were divided into three groups as per Th1 cell levels: Th1 level of <22.8 as Low; 22.8 to <28.8 as Middle, and 28.8 or greater as High group. The study patients received daily dose of tacrolimus 1-3 mg based on initial Th1/Th2 cell ratio.

RESULTS

The clinical pregnancy rates of Low, Middle, and High groups were 48.8%, 43.9%, and 33.3%, respectively (P=NS), with tacrolimus treatment. The ongoing pregnancy/delivery rate of Low group (46.3%) was significantly higher than that of High group (21.4%, P<.05). Middle group (34.3%) had higher success rate than High group, albeit without statistical significant.

CONCLUSION

We confirm our previous report that Th1/Th2 ratio can predict ART outcomes in patients with RIF and immunosuppressant treatment with tacrolimus, and peripheral blood Th1 cell levels were negatively correlated with pregnancy outcome.

Perinatal outcomes of patients who achieved pregnancy with a morphologically poor embryo via assisted reproductive technology

PURPOSE

To learn more about the perinatal outcomes of conception via the use of low-grade embryos, we evaluated the relationship between the status of transferred embryos and the resultant perinatal outcomes.

METHODS

A total of 340 patients who achieved pregnancy via ART treatment and consequently delivered in our clinic between April 2009 and March 2014 were recruited for this study. Patients were divided into two groups according to a morphological assessment of the transferred embryos, which relegated 79 patients into a poor-embryo group with the remainders (n = 261) placed into a good-embryo group.

RESULTS

The mean maternal age for the poor-embryo group was 36.0 years, which was similar to the good-embryo group (36.8). In both groups, the percentages of fresh ET cycles were similar. The values for the mean birth weight and birth height of infants in the poor-embryo group were 3055 g and 50.3 cm, respectively, and there were no significant differences with the good-embryo group. The umbilical blood gas analysis in the poor-quality group was similar to that in the good-embryo group. There were no obvious major anomalies among the infants of either group.

CONCLUSIONS

The perinatal outcomes of the poor-embryo group were comparable to those of the good-embryo group. Based on these results, we can provide qualified assurance for a normal perinatal outcome to patients who had no choice but to undergo embryo transfer with a poor-quality embryo.

The Effect of a Newly Designed Needle on the Pain and Bleeding of Patients During Oocyte Retrieval of a Single Follicle

BACKGROUND

The purpose of this study was to evaluate the effect of needle type on pain and bleeding during oocyte pick-up (OPU).

METHODS

From May through November 2013, patients undergoing OPU from a single follicle without any analgesic treatment were including this study. Eligible patients (n=75) were randomized 1:1 to undergo the procedure with either a reduced needle (17 gauge body, 20 gauge tip; RN group) or a standard needle (19 gauge; SN group). Overall pain was assessed by patients using a visual analogue scale (VAS), and vaginal bleeding after the procedure was recorded. Fisher exact, t-test or Wilcoxon test were used, and p<0.05 was considered to be statistically significant.

RESULTS

The percentage of mature oocytes was 86.5% in the RN group and 91.7% in the SN group. Pain during OPU was significantly lower in the RN group than in the SN group (mean VAS score±SD: 3.2±2.0 cm vs. 4.9±2.2 cm, p<0.01; mean±SD). The frequency of vaginal bleeding was also significantly lower in the SN group (26.3% vs. 48.6%; p<0.05). The frequency of bleeding in the RN group was also significantly lower than that in the SN group (26.3% vs. 48.6%; p<0.05). No significant differences were found between the two groups with regard to fertilization and pregnancy rates.

CONCLUSION

The newly designed needle significantly reduced pain and vaginal bleeding associated with single-follicle OPU in patients receiving no analgesic treatment, in comparison with a standard needle. The RN had no adverse effect on the quality of retrieved oocytes.

Clomiphene citrate affects the receptivity of the uterine endometrium

Purpose

To investigate whether clomiphene citrate (CC) affects uterine receptivity or not, we evaluated pregnancy rates (PR) during the hormone replacement cycle (HRC) according to the period between the last day of CC administration and the day of embryo transfer (ET).

Methods

From March 2008 through March 2010, a total of 378 treatment cycles among 378 patients who received CC and had to avoid fresh ET due to a thin uterine endometrium were recruited. All patients underwent thawed ET using HRC. PRs were evaluated according to the period between the last CC treatment and the day of ET.

Results

PR for the groups in which the period between the last CC treatment and the day of ET increased to more than 91 days were significantly higher than that for group in which the period was less than 90 days (p < 0.05).

Conclusions

A lower PR was shown by the patients who underwent thawed ET in the HRC within 90 days after their last CC treatment, which shows that CC affects the receptivity of the uterine endometrium.

Cryopreservation of oocytes and embryos

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

Advanced scheduling for zygote intrafallopian transfer is possible via the use of a hormone replacement cycle for patients who have experienced repeated implantation failures

PURPOSE

Zygote intrafallopian transfer (ZIFT) is an effective option for patients who have experienced repeated implantation failures (RIF) in assisted reproductive technology (ART) treatment. However, advance planning for the day of the operation can be problematic. Using a hormone replacement cycle (HRC) makes it possible to plan for the day of ZIFT. In the present study, we evaluated whether HRC-ZIFT is useful for RIF patients who have experienced difficulties obtaining morphologically good embryos in vitro.

METHODS

A total of 55 patients with a history of five or more unsuccessful transfers received HRC-ZIFT between June 2008 and June 2013. The oocyte pick-ups were performed and the oocytes showing two pronuclei (2PN) were cryopreserved. After receiving more than five 2PN oocytes, the operation day was scheduled in advance, and as a consequence, a HRC was started and ZIFT was performed. The clinical outcomes were evaluated.

RESULTS

The average age of the patients was 39.3 years, and the previous OPU and ET attempts numbered 7.5 and 6.9, respectively. The number of previously transferred embryos was 11.8, and the number of morphologically good embryos (MGEs) was only 1.2. The number of transferred 2PN oocytes was 6.7, and the subsequent pregnancy rate was 23.6 %. No ectopic or multiple pregnancies were observed, but there were 6 cases of miscarriage.

CONCLUSION

Among RIF patients, in particular those who have difficulty obtaining MGEs in vitro, ZIFT might be a useful option. The HRC allows patients and medical staff to plan for the operation day in advance.

Using a mild stimulation protocol combined with clomiphene citrate and recombinant follicle-stimulating hormone to determine the optimal number of oocytes needed to achieve pregnancy and reduce the concerns of patients

Purpose

The purpose of this study was to investigate how many oocytes are needed to achieve an adequate pregnancy rate per 1 oocyte retrieval cycle in mild ovarian stimulation.

Methods

This protocol consisted of clomiphene citrate and recombinant-follicle-stimulating hormone injection without a gonadotropin-releasing hormone-antagonist. From January 2009 through December 2010, there were 1,227 women who underwent assisted reproductive technologies treatment with mild stimulation at the Sugiyama Clinic. The overall pregnancy rate per single oocyte retrieval cycle was evaluated using both fresh and cryopreserved-and-thawed embryos according to the retrieved oocyte number.

Results

According to the retrieved oocyte number, a total of 1,227 cycles were divided into 4 groups: group A (the oocyte number <4; 433 cycles), group B (the oocyte number = 4, 5; 317 cycles), group C (the oocyte number = 6, 7; 206 cycles), and group D (the oocyte number ≥8; 271 cycles). The overall pregnancy rates for groups A, B, C, and D were 22.2, 42.9, 52.4, and 56.0 %, respectively, the rates for groups C and D were significantly higher than that for group A (p < 0.01).

Conclusions

The optimal number of retrieved oocytes proved to be between 6 and 7 for the patients who received our milder stimulation protocol and experienced no reduction in their overall pregnancy rate.

Hyaluronan-enriched transfer medium improves outcome in patients with multiple embryo transfer failures

PURPOSE

To ascertain whether the use of hyaluronan-enriched transfer medium (HETM) improves pregnancy and implantation rates among embryo transfer patients with a history of multiple implantation failures.

METHODS

Patients (n = 314) under the age of 40 and with a history of multiple unsuccessful embryo transfers were enrolled. There were three groups of patients: those undergoing fresh embryo transfer (fresh ET [n = 111]), those undergoing vitrified-warmed ET in the natural cycle (WET-N [n = 101]) and those undergoing WET in a hormone replacement cycle (WET-H [n = 102]). On the day of ET, patients were randomized to HETM (0.5 mg/ml hyaluronan) or control medium containing no hyaluronan. Only patients with good quality embryos on day 3 were included.

RESULTS

For all three patients groups (fresh ET, WET-N and WET-H) pregnancy rates (37.5 %, 31.4 % and 41.2 %, respectively) were significantly higher when using HETM compared with control medium (10.9 %, 10.0 % and 15.7 %, respectively; p < 0.05), and implantation rates when using HETM were also significantly higher compared with control medium (p < 0.05). Miscarriage rates were similar in both groups.

CONCLUSION

HETM significantly increased pregnancy and implantation rates among embryo transfer patients with a history of multiple unsuccessful implantations-regardless of method used to prepare the endometrium.

A programmed schedule of oocyte retrieval using mild ovarian stimulation (clomiphene citrate and recombinant follicle-stimulating hormone)

PURPOSE

The purpose was to establish a mild ovarian stimulation protocol that would help assisted reproductive technology (ART) units to avoid scheduling on weekends.

METHODS

This protocol directed patients to take 50 mg/day of clomiphene citrate between days 3 and 7 of the menstrual cycle: 225 IU of recombinant follicle-stimulating hormone (rec-FSH) were administered on days 3, 5 and 7; human chorionic gonadotropin (hCG) was administered on day 9; and, oocyte pick-up (OPU) was planned for day 11. From October 2008 through October 2009, 514 women underwent ART treatment with mild stimulation at the Sugiyama Clinic, and we evaluated whether OPU was accomplished on the planned day.

RESULTS

Of all the treatment cycles, 419 (81.5%) underwent OPU on day 11 (scheduled group). Additional rec-FSH administration was needed in 83 cycles, in which case OPU was performed on day 12 or later. In 12 cycles, OPU was canceled. The unscheduled group (n = 95) consisted of delayed OPU cycles and canceled cycles. Of all treatment cycles, 332 cycles in the scheduled group and 68 cycles in the unscheduled group underwent embryo transfer, with 81 and 16, respectively, resulting in pregnancies.

CONCLUSIONS

Using this protocol, OPU was performed on the scheduled day in about 80% of the cycles. Most weekend scheduling of OPU can be avoided using this mild stimulation.

Benefit and risk of application of European tissue management regulation in ART

The application of the European Tissues and Cells Directive requires that a high standard of quality and safety be applied to all tissue establishments, including that of assisted reproductive centres. In the countries where the Directive has been implemented, changes in the ART clinic and laboratory procedures have been made. However, many requirements stipulated in the Directive are already in place in some European countries and are mandatory by the country specific laws, while some other requirements have been recently implemented. In this article the benefits and the potential risks of the Directive implementation on the efficacy, safety and cost of all the different assisted reproductive technologies performed, including cryopreservation techniques and storage policies have been widely analysed. The feasibility of the implementation of some of the specific requirements when considering the delicate issues of reproductive cells in contrast to other cells or tissues covered by the Directive has been evaluated.

Efficiency of aseptic open vitrification and hermetical cryostorage of human oocytes

The present study reports, as far as is known for the first time, the safety of UV sterilization of liquid nitrogen and hermetical cryostorage of human oocytes by comparing the efficiency of fresh and vitrified sibling oocytes of infertile patients. A prospective randomized study on sibling oocytes of 31 patients was carried out. Metaphase-II oocytes were randomized for intracytoplasmic sperm injection and the supernumerary sibling oocytes were vitrified using a novel Cryotop aseptic procedure (UV liquid nitrogen sterilization and hermetical cryostorage). After unsuccessful attempts with fresh oocytes, vitrified sibling oocytes were injected. Mean outcome measures observed were fertilization, cleavage and top-quality embryo rates. No significant differences were observed between the fresh and vitrified-warmed sibling oocytes: oocyte fertilization was 88.3% versus 84.9%; cleavage 72.6% versus 71.0%; top-quality embryos 33.8% versus 26.3% and mean number of transferred embryos 2.6 ± 0.1 versus 2.5 ± 0.1, respectively. Clinical pregnancy rate per cycle with vitrified-warmed oocytes was 35.5% (implantation rate 17.1%) and seven healthy babies were born. This study demonstrated that UV liquid nitrogen sterilization and hermetical cryostorage does not adversely affect the developmental competence of vitrified oocytes, allowing safe aseptic open vitrification applicable under strict directives on tissue manipulation.

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

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

Cryopreservation of mammalian embryos: Advancement of putting life on hold

Rodent transgenesis and human-assisted reproductive programs involve multistep handling of preimplantation embryos. The efficacy of production and quality of results from conventionally scheduled programs are limited by temporal constraints other than the quality and quantities of embryos per se. The emergence of vitrification, a water ice-free cryopreservation technique, as a reliable way to arrest further growth of preimplantation embryos, provides an option to eliminate the time constraint. In this article, current and potential applications of cryopreservation to facilitate laboratory animal experiments, colony management, and human-assisted reproductive programs are reviewed. Carrier devices developed for vitrification in the last two decades are compared with an emphasis on their physical properties that infer cooling rate of samples and sterility assurance. Biological impacts of improved cryopreservation on preimplantation embryos are also discussed.

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

OBJECTIVES

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

STUDY DESIGN

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

RESULTS

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

CONCLUSIONS

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