Cryopreservation of Human Embryos

Chinese experts' consensus guideline on preimplantation genetic testing of monogenic disorders

Recent developments in molecular biological technologies and genetic diagnostic methods, accompanying with updates of relevant terminologies, have enabled the improvements of new strategies of preimplantation genetic testing for monogenic (single gene) disorders (PGT-M) to prevent the transmission of inherited diseases. However, there has been much in the way of published consensus on PGT-M. To properly regulate the application of PGT-M, Chinese experts in reproductive medicine and genetics have jointly developed this consensus statement. The consensus includes indications for patient selection, genetic and reproductive counseling, informed consent, diagnostic strategies, report generation, interpretation of results and patient follow-ups. This consensus statement serves to assist in establishment of evidence-based clinical and laboratory practices for PGT-M.

Vitrification within a nanoliter volume: oocyte and embryo cryopreservation within a 3D photopolymerized device

Purpose

Vitrification permits long-term banking of oocytes and embryos. It is a technically challenging procedure requiring direct handling and movement of cells between potentially cytotoxic cryoprotectant solutions. Variation in adherence to timing, and ability to trace cells during the procedure, affects survival post-warming. We hypothesized that minimizing direct handling will simplify the procedure and improve traceability. To address this, we present a novel photopolymerized device that houses the sample during vitrification.

Methods

The fabricated device consisted of two components: the Pod and Garage. Single mouse oocytes or embryos were housed in a Pod, with multiple Pods docked into a Garage. The suitability of the device for cryogenic application was assessed by repeated vitrification and warming cycles. Oocytes or early blastocyst-stage embryos were vitrified either using standard practice or within Pods and a Garage and compared to non-vitrified control groups. Post-warming, we assessed survival rate, oocyte developmental potential (fertilization and subsequent development) and metabolism (autofluorescence).

Results

Vitrification within the device occurred within ~ 3 nL of cryoprotectant: this volume being ~ 1000-fold lower than standard vitrification. Compared to standard practice, vitrification and warming within our device showed no differences in viability, developmental competency, or metabolism for oocytes and embryos. The device housed the sample during processing, which improved traceability and minimized handling. Interestingly, vitrification-warming itself, altered oocyte and embryo metabolism.

Conclusion

The Pod and Garage system minimized the volume of cryoprotectant at vitrification—by ~ 1000-fold—improved traceability and reduced direct handling of the sample. This is a major step in simplifying the procedure.

Supplementary information

The online version contains supplementary material available at 10.1007/s10815-022-02589-8.

The emergence of temporality in attitudes towards cryo-fertility: a case study comparing German and Israeli social egg freezing users

Assistive reproductive technologies are increasingly used to control the biology of fertility and its temporality. Combining historical, theoretical, and socio-empirical insights, this paper aims at expanding our understanding of the way temporality emerges and is negotiated in the contemporary practice of cryopreservation of reproductive materials. We first present an historical overview of the practice of cryo-fertility to indicate the co-production of technology and social constructions of temporality. We then apply a theoretical framework for analysing cryobiology and cryopreservation technologies as creating a new epistemic perspective interconnecting biology and temporality. Thereafter, we focus on the case of 'social egg freezing' (SEF) to present socio-empirical findings illustrating different reproductive temporalities and their connection to the social acceptance of and expectations towards the practice. SEF is a particularly interesting case as it aims to enable women to disconnect their reproductive potential from their biological rhythms. Based on 39 open interviews with Israeli and German SEF users, the cross-cultural comparative findings reveal three types of attitudes: postponing motherhood/reproductive decisions (German users); singlehood and "waiting" for a partner (Israeli and German users); and the planning of and hope for multiple children (Israeli users). For theory building, this analysis uncovers temporality formations embedded in gender and reproductive moral values; including the 'extended present', 'waiting', and 'reproductive futurism'. We conclude by discussing the contribution of our findings by advancing the theoretical framework of 'cryopolitics' highlighting the theoretical implications and importance of gendered and cultural imaginaries (re)constructing medical technological innovations and related temporalities.

Natural cycles achieve better pregnancy outcomes than artificial cycles in non-PCOS women undergoing vitrified single-blastocyst transfer: a retrospective cohort study of 6840 cycles

PURPOSE

To identify the optimal method for endometrial preparation in vitrified single-blastocyst transfer (VSBT) cycles.

METHODS

This was a retrospective cohort study for non-PCOS patients who underwent VSBT cycles from March 2015 to November 2019 in an academic reproductive medical center. A total of 6840 VSBT cycles were enrolled and classified into two groups according to different endometrial preparation methods.

RESULTS

The non-PCOS patients who underwent VSBT showed a significantly higher clinical pregnancy rate (61.96% vs 56.85%, p < 0.001) and live birth rate (49.09% vs 39.86%, p < 0.001), as well as a statistically lower early miscarriage rate (12.02% vs 18.08%, p < 0.001) in the natural cycle (NC) group compared with the artificial cycle (AC) group. Multivariable analysis further confirmed that NC was associated with an increased likelihood of clinical pregnancy (adjusted odds ratio (aOR) 0.852, 95% confidence interval (CI) 0.765-0.949, p = 0.004) and live birth (aOR 0.746, 95% CI 0.669-0.832, p < 0 .001), but decreased early miscarriage occurrence (aOR 1.447, 95% CI 1.215-1.724, p < 0.001) compared to AC.

CONCLUSIONS

Our study demonstrated that non-PCOS patients could benefit from NC in vitrified blastocyst transfer. Increased clinical pregnancy rate and decreased early miscarriage rate led to a significantly higher live birth rate in NC patients compared with AC with our present protocol.

Slow freezing should not be totally substituted by vitrification when applied to day 3 embryo cryopreservation: an analysis of 5613 frozen cycles

PURPOSE

This study aimed to compare slow freezing (SF) and vitrification (VT) techniques for day 3 embryo cryopreservation in infertile couples.

METHODS

This retrospective cohort study enrolled 5613 infertile patients, with 7862 frozen-thawed day 3 embryos and 3845 vitrified-warmed day 3 embryos, from 2010 to 2014, at a single center. The rates of embryo survival, pregnancy, implantation, miscarriage, live birth, and live birth weight were compared between the two groups.

RESULTS

A total of 5613 cycles with 5520 transfers were analyzed. Using SF, the rates of overall embryo survival and fully intact blastomeres were lower than those in VT (91.5 vs. 97.4 % and 68.7 vs. 92.3 %, respectively). The rate of good quality embryos after thawing/warming was lower in SF than in VT. In single frozen embryo transfer cycles (FETs), the pregnancy and implantation rates were similar between the two groups (35.0 vs. 40.8 % and 34.6 vs. 35.9 %, respectively). In double FETs, the pregnancy rate per cycle was also similar between the groups (58.8 vs. 58.4 %). The implantation rate per embryo transfer was significantly higher with SF than with VT (38.8 vs. 34.6 %). With adjustment for maternal age and the number of good quality embryos, differences in implantation rate remained significant (adjusted P value, SF vs. VT P < 0.05). No independent effect was found for the method of cryopreservation on the pregnancy rate. No significant differences in the rates of miscarriage, live birth, and live birth weight were observed between the two techniques.

CONCLUSIONS

Despite the significantly low embryo survival rate, fully intact blastomere rate, and good quality embryo rate in SF, the pregnancy and implantation rates were not adversely affected in single and double FETs. SF yielded an equivalent miscarriage rate, live birth rate, and live birth weight compared with VT. The SF protocol to cryopreserve day 3 embryos still should be considered.

Fertility preservation and minimizing reproductive damage in cancer survivors

Recent advances in oncology have helped in the survival and cure of increasing numbers of childhood cancer patients and those during their reproductive age period. This has increased the need to improve existing technology, and prompted the search for new technologies, to minimize the gonadotoxic effects of cancer treatment and preserve human fertility. Conservative surgical approaches for cancer treatment have been widely accepted following progress in early detection of cancer and accumulating long-term outcome safety data. Gonadal suppression to increase resistance to cancer treatment by gonadotropin analogues and sex hormones has been suggested. However, while this is unlikely to be effective in males, there is no general consensus on its success in the female. Fertility preservation options for both male and female patients include cryopreservation of embryos, gametes and gonads. While embryo cryopreservation is a well-established and successful technique, there are several obvious limitations. Gamete cryopreservation is very successful in males (sperm freezing) while still experimental in females (oocyte freezing), with growing evidence suggesting its potential success. Gonadal cryopreservation is still in its early stages of experimental development, both in males (testicular tissue cryopreservation and in vitro spermatogenesis) and female (ovarian tissue cryopreservation and in vitro follicular maturation).

Factors related to clinical pregnancy after vitrified-warmed embryo transfer: a retrospective and multivariate logistic regression analysis of 2313 transfer cycles

STUDY QUESTION

What factors does multivariate logistic regression show to be significantly associated with the likelihood of clinical pregnancy in vitrified-warmed embryo transfer (VET) cycles?

SUMMARY ANSWER

Assisted hatching (AH) and if the reason to freeze embryos was to avoid the risk of ovarian hyperstimulation syndrome (OHSS) were significantly positively associated with a greater likelihood of clinical pregnancy.

WHAT IS KNOWN ALREADY

Single factor analysis has shown AH, number of embryos transferred and the reason of freezing for OHSS to be positively and damaged blastomere to be negatively significantly associated with the chance of clinical pregnancy after VET. It remains unclear what factors would be significant after multivariate analysis.

STUDY DESIGN, SIZE, DURATION

The study was a retrospective analysis of 2313 VET cycles from 1481 patients performed between January 2008 and April 2012. A multivariate logistic regression analysis was performed to identify the factors to affect clinical pregnancy outcome of VET.

PARTICIPANTS/MATERIALS, SETTING, METHODS

There were 22 candidate variables selected based on clinical experiences and the literature. With the thresholds of α entry = α removal= 0.05 for both variable entry and variable removal, eight variables were chosen to contribute the multivariable model by the bootstrap stepwise variable selection algorithm (n = 1000). Eight variables were age at controlled ovarian hyperstimulation (COH), reason for freezing, AH, endometrial thickness, damaged blastomere, number of embryos transferred, number of good-quality embryos, and blood presence on transfer catheter. A descriptive comparison of the relative importance was accomplished by the proportion of explained variation (PEV).

MAIN RESULTS AND THE ROLE OF CHANCE

Among the reasons for freezing, the OHSS group showed a higher OR than the surplus embryo group when compared with other reasons for VET groups (OHSS versus Other, OR: 2.145; CI: 1.4-3.286; Surplus embryos versus Other, OR: 1.152; CI: 0.761-1.743) and high PEV (marginal 2.77%, P = 0.2911; partial 1.68%; CI of area under receptor operator characteristic curve (ROC): 0.5576-0.6000). AH also showed a high OR (OR: 2.105, CI: 1.554-2.85) and high PEV (marginal 1.97%; partial 1.02%; CI of area under ROC: 0.5344-0.5647). The number of good-quality embryos showed the highest marginal PEV and partial PEV (marginal 3.91%, partial 2.28%; CI of area under ROC: 0.5886-0.6343).

LIMITATIONS, REASONS FOR CAUTION

This was a retrospective multivariate analysis of the data obtained in 5 years from a single IVF center. Repeated cycles in the same woman were treated as independent observations, which could introduce bias. Results are based on clinical pregnancy and not live births. Prospective analysis of a larger data set from a multicenter study based on live births is necessary to confirm the findings.

WIDER IMPLICATIONS OF THE FINDINGS

Paying attention to the quality of embryos, the number of good embryos, AH and the reasons for freezing that are associated with clinical pregnancy after VET will assist the improvement of success rates.

Cryopreservation of human genetic material

Up-to-date cryopreservation is a central component of contemporary human-assisted reproduction and fertility preservation technologies. Presently, the preservation of seminal and testicular spermatozoa, embryos, and oocytes can be readily achieved with a high functional survival rate. Preservation of the ovarian cortex containing a greater number of female germ cells is an experimental procedure under extensive investigation in many centers. All these techniques are used for various purposes like optimization of assisted reproduction, provision of donor gametes, fertility preservation for cancer patients and aging women, and posthumous reproduction. Here, we present a comprehensive review of the various applications of gamete, embryo, and ovarian tissue cryopreservation and discuss their basic biological principles, practical applicability, and limitations.

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.

Cryopreservation of primate embryonic stem cells with chemically-defined solution without Me2SO

Human embryonic stem (hES) cells are expected to be useful in the fields of regenerative medicine and tissue engineering due to their pluripotency. Therefore, it is necessary to establish highly efficient and reliable methods for the cryopreservation of hES cells. We have cryopreserved cynomolgus and human ES cells by the vitrification method, using a chemically-defined dimethyl sulfoxide (Me(2)SO)-free and serum-free medium composed of Euro-Collins solution as a base medium and 40% (v/v) ethylene glycol (EG) and 10% (w/v) polyethylene glycol (PEG) as cryoprotectants. When the vitrification and the cryoprotectants were combined, the recovery ratio of hES cells was 22.9+/-7.7%, compared to 0.4+/-0.2% when the conventional slow-freezing method was used. After the cryopreservation and thawing cycle, hES cells were easily cultured and expressed undifferentiated cell markers such as Nanog, Oct-4, SSEA-4, and alkaline phosphatase activity after several subculturing steps. We also found that the pluripotency of hES cells was maintained, as demonstrated by teratoma formation of ES cells transplanted into severe combined immunodeficient (SCID) mice. Thus, we conclude that we have successfully cryopreserved primate ES cells with high efficiency using a Me(2)SO-free, chemically-defined medium.

Increased risk of blastogenesis birth defects, arising in the first 4 weeks of pregnancy, after assisted reproductive technologies

BACKGROUND

The reasons for increased birth defect prevalence following in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are largely unknown. Classification of birth defects by pathology rather than organ system, and examination of the role of embryo freezing and thawing may provide clues to the mechanisms involved. This study aimed to investigate these two factors.

METHOD

Data on 6946 IVF or ICSI singleton pregnancies were linked to perinatal outcomes obtained from population-based data sets on births and birth defects occurring between 1991 and 2004 in Victoria, Australia. These were compared with 20,838 outcomes for singleton births in the same population, conceived without IVF or ICSI. Birth defects were classified according to pathogenesis.

RESULTS

Overall, birth defects were increased after IVF or ICSI [adjusted odds ratio (OR) 1.36; 95% CI: 1.19-1.55] relative to controls. There was no strong evidence of risk differences between IVF and ICSI or between fresh and thawed embryo transfer. However, a specific group, blastogenesis birth defects, were markedly increased [adjusted OR 2.80, 95% CI: 1.63-4.81], with the increase relative to the controls being significant for fresh embryo transfer (adjusted OR 3.65; 95% CI: 2.02-6.59) but not for thawed embryo transfer (adjusted OR 1.60; 95% CI: 0.69-3.69).

CONCLUSION

Our findings suggest that there is a specific risk of blastogenesis birth defects arising very early in pregnancy after IVF or ICSI and that this risk may be lower with use of frozen-thawed embryo transfer.

Stimulation day-six serum estradiol: a predictive indicator for the probability of embryo cryopreservation in IVF/ICSI cycles

OBJECTIVE

To evaluate the predictive value of stimulation day six serum estradiol (E2) for the probability of embryo cryopreservation after fresh embryo transfer in intracytoplasmic sperm injection (ICSI) cycles.

SUBJECTS AND METHODS

The study included 282 ICSI cycles for different causes of infertility, provided that the age of the female partner was <40 years and her basal follicle stimulating hormone <10 IU/L.

SETTING

Alexandria IVF/ICSI center.

MAIN OUTCOME MEASURES

Primary outcome measures are stimulation day-six serum E2, and rate of embryo cryopreservation, after transfer of three good-quality embryos. Secondary outcome measures are pregnancy rate per fresh embryo transfer, and other intermediate variables of the ICSI cycle.

RESULTS

Patients were stratified into three groups according to day-six serum E2 levels: Group I with values <400 pg/mL; Group II, between 400 and 900; and Group III with values >900. The mean number of oocytes retrieved was 6.3, 8.9, and 12.4; the mean number of obtained embryos was 3.3, 4.8, and 6.7; and pregnancy rates were 18.1, 36.2, and 44.7% in the three groups, respectively. Rate of embryo cryopreservation, after transfer of three good-quality embryos was 70.7% in Group III, and 26.5% in Group I. (P = 0.01). The negative predictive value of day-six E2 <400 pg/mL for freezing was 83% while day-six serum E2 >900 pg/mL has a sensitivity of 55%, specificity of 72% and positive predictive value of 50% for embryo freezing.

CONCLUSION

Higher stimulation day-six estradiol was associated with a higher probability of cryopreservation, and a higher pregnancy rate.

A case of oocyte and embryo vitrification resulting in clinical pregnancy

OBJECTIVE

To examine a case of clinical pregnancy following oocyte and day 3 embryo vitrification.

DESIGN

Case report.

SETTING

Huntington Centro de Medicina Reprodutiva, a private infertility clinic, in São Paolo, Brazil.

PATIENT(S)

A 31-year-old woman, gravida 1, para 1, with polycystic ovary syndrome.

INTERVENTION(S)

In vitro fertilization with oocyte and embryo vitrification.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy defined as fetal cardiac activity on ultrasound examination.

RESULT(S)

Transvaginal ultrasound examination, at 7 6/7 weeks, revealed a single live intrauterine pregnancy with positive cardiac activity.

CONCLUSION(S)

Although further research is needed, this case suggests that repeat vitrification and warming of oocytes and embryos not only are possible but can result in pregnancy.

Favorable pregnancy, delivery, and implantation rates experienced in embryo donation programs in the United States

OBJECTIVE

To document the numbers of donated frozen ETs performed and the pregnancy, birth, and embryo implantation rates seen in four infertility clinics and three embryo donation agencies in the United States.

DESIGN AND SETTING

Case series. Four infertility clinics and three embryo donation agencies in the United States contributed data from their first year of available information through calendar year 2006. The programs reported numbers of donated frozen ETs, numbers of pregnancies delivered from these transfers, and numbers of these pregnancies lost to miscarriage or stillbirth. For each pregnancy, the programs reported the number of gestational sacs identified and the number of resulting live births.

PATIENT(S)

N/A.

INTERVENTION(S)

N/A.

MAIN OUTCOME MEASURE(S)

Pregnancy rate, delivery rate per ET, implantation rate, live birth rate per embryo transferred, and "implantation potential" (gestational sacs identified per embryo thawed).

RESULT(S)

These programs performed 702 ETs, resulting in 314 clinical pregnancies (44.7%) and 249 deliveries (35.5%). With 3,103 embryos thawed and 2,078 embryos transferred, the programs experienced an implantation rate of 19.9%, an implantation potential of 11.8%, and a live birth rate per embryo transferred of 15.0%.

CONCLUSION(S)

In this largest case series yet published, the pregnancy, delivery, and implantation rates for embryo donation compare favorably with rates reported from autologous IVF procedures.

Cryopreservation of human embryos by vitrification or slow freezing: a systematic review and meta-analysis

OBJECTIVE

To examine the literature systematically in order to identify prospective comparative trials answering the following question: Is vitrification of human embryos associated with a higher postthawing survival rate as compared with slow freezing?

DESIGN

Systematic review and meta-analysis.

SETTING

University-based hospital.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Vitrification versus slow freezing for cryopreservation of human embryos.

MAIN OUTCOME MEASURE(S)

Postthawing survival rate.

RESULT(S)

Four eligible studies were identified, three of which were randomized controlled trials. Overall, the current review summarizes information from 8,824 cryopreserved human cleavage stage embryos/blastocysts (vitrification: n = 7,482; slow freezing: n = 1,342). Survival rate of cleavage stage embryos was significantly higher after vitrification as compared with slow freezing (odds ratio 15.57, 95% confidence interval 3.68-65.82; random effects model). Postthawing survival rate of vitrified blastocysts was significantly higher compared with that observed with slow freezing (odds ratio 2.20, 95% confidence interval 1.53-3.16; fixed effects model).

CONCLUSION(S)

Vitrification appears to be associated with a significantly higher postthawing survival rate than slow freezing. Further prospective trials are necessary to confirm the above results and, in addition, allow the evaluation of the two cryopreservation methods in terms of pregnancy achievement.

Highly efficient vitrification for cryopreservation of human oocytes and embryos: The Cryotop method

Vitrification is frequently referred to as a novel technology of cryopreservation in embryology, although some young embryologists were born after its first successful application. Unfortunately, in spite of the accumulated evidence regarding its enormous potential value, most domestic animal and human laboratories use exclusively the traditional slow-rate freezing with its compromised efficiency and inconsistency. The purpose of this paper is to clarify terms and conditions, to summarize arguments supporting or disapproving the use of vitrification, and to outline its role among assisted reproductive technologies. To provide evidence for the potential significance of vitrification, achievements with the Cryotop technology, an advanced version of the "minimal volume approaches" is analyzed. This technology alone has resulted in more healthy babies after cryopreservation of blastocysts than any other vitrification technique, and more successful human oocyte vitrification resulting in normal births than any other cryopreservation method. The value of this method is also demonstrated by achievements in the field of domestic animal embryology. A modification of the technique using a hermetically sealed container for storage may help to eliminate potential dangers of disease transmission and open the way for widespread application for cryopreservation at all phases of oocyte and preimplantation embryo development in mammals.