Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Equivalent outcomes of human oocytes after vitrification or slow freezing with a modified rehydration protocol

BACKGROUND

According to data from numerous research studies and reviews, the efficiency of the oocyte slow-freezing method is believed to be compromised. Here, we attempt to challenge this notion by showing our retrospective evaluation of the efficiency of the traditional vs. successfully modified method of slow-frozen oocyte recovery compared with that of vitrified oocytes. Specifically, we compared the efficiency of a modified thawing/rehydration system applied to oocytes that had already been slow-frozen with the effects of oocyte vitrification. Moreover, we verified this comparison using chemical activation of slow-frozen vs. vitrified oocytes and parthenogenetic embryo development.

RESULTS

Twenty-two and 73 thawing cycles of slow-frozen oocytes were performed using traditional and modified rehydration methods, respectively. For comparison, 105 warming cycles of vitrified oocytes were analyzed. The survival rate of oocytes subjected to the traditional rehydration method was 65.1%. In contrast, significantly higher ratios of 89.8% and 89.7% of oocytes survived the thawing/warming procedure performed according to the modified rehydration procedure or vitrification, respectively (P ≤ 0.0001). Clinical pregnancy and implantation rates tended to be higher after a transfer of embryos developed in the modified rehydration group vs. traditional rehydration group (33.8% and 25.5% vs. 23.5% and 13.8%, respectively) and were comparable to vitrification effects (30.1% and 26.6%). Transfer of embryos developed after modified post-thawing rehydration method resulted in 23 births with 25 healthy and one preterm baby, not significantly different from 28 births reported after oocyte vitrification. Slow-frozen oocytes that were chemically activated after the superior modified rehydration method gave similar survival (91.9% vs. 99.0%), activation (76.0% vs. 64.6%) and blastocyst rates (15.2% vs. 9.4%) in comparison with vitrified oocytes, respectively.

CONCLUSIONS

The modified post-thawing rehydration method applied to slow-frozen oocytes offers benefits in terms of higher oocyte survival, fertilization, and development or activation rates, comparable to the respective measures of vitrified oocytes and, in clinical settings, high pregnancy, implantation, and birth rates. It may bring new hope to patients who have slow-frozen oocytes stored in IVF clinics.

A diluted one-step warming protocol: survival of vitrified blastocyst

PURPOSE

The objective of this study was to compare the effects of two warming protocols (three step vs. one-step) on re-expansion and post-warming survival of human blastocysts previously vitrified using the standard vitrification protocol.

METHODS

One hundred vitrified blastocysts were included in the study; 50 blastocysts were warmed using the standard warming protocol, and 50 were warmed using the diluted one-step warming protocol (DS 37 °C, 3 min; WS RT 5 min; culture dish until embryo transfer).

RESULTS

There was no significant difference in survival 2 h post-warming between the standard warming protocol and the diluted one-step warming protocol (98% vs 94%; p = 0.3), nor was there any difference in the number of embryos that were completely re-expanded, hatching or hatched when evaluated 2 h post-warming (84% vs 80%; p = 0.6). Those results indicate that vitrified blastocysts were able to survive equally between the two investigated protocols.

CONCLUSION

The diluted one-step warming of vitrified blastocysts in 0.5 M sucrose showed no negative effects on embryo re-expansion and post-warming embryo survival when compared with the standard warming method. Therefore, the elimination of the first step of the standard warming procedure (TS, 37 °C, 1 min), the most difficult at a practical level, not only allows the reduction of the execution time, but above all, reduces the learning curve while maintaining effectiveness.

Evaluation of Women's Awareness and Knowledge of Planned Oocyte Cryopreservation at Different Sociocultural Levels: A Cross-Sectional Survey

Objective: This study evaluated awareness and knowledge of planned oocyte cryopreservation (POC) among Turkish women across diverse sociocultural backgrounds. Design: This is a cross-sectional survey with a 56-item self-administered electronic questionnaire. Setting: Istanbul, Turkiye, June to September 2022. Population: The study evaluated 915 participants between 21 and 45 years. Methods: Women completed a 56-item self-administered online electronic questionnaire survey to identify their demographic information, perspective on family planning, future fertility expectations/plans, oocyte freezing, and degree of knowledge. Main Outcome Measures: Comparison of participants considering and not considering POC. Results: A total of 464 (50.7%) women indicated an intent to undergo POC in the future, with statistically significantly higher university graduates in the group clearly considering POC (p=0.044) and a higher rate of singles indicating an intent to POC. A total of 546 (59.7%) women planned to have children in the future; the participants considered the age of 39.37 (±5.01) as "old" for pregnancy; 748 (81.7%) of the participants thought that the information about age-related fertility decline and POC should be a part of the annual gynecological examination. The level of knowledge about family planning/postponing fertility and POC between the two groups showed that the group considering POC provided significantly more accurate responses to seven items (5th, 6th, 7th, 10th, 11th, 14th, and 17th questions). The group not considering POC answered correctly, "What is the rate of spontaneous female conception?" (p=0.047). Conclusion: The target population expected to benefit from POC in our country had low knowledge and awareness of age-related fertility decline and POC. Most women expected the information to be a part of the annual gynecological examination. The main determinants of the knowledge score and considering POC are education level and relationship status.

Use and understanding of AI in the ART laboratory: an international survey

RESEARCH QUESTION

What is the awareness, adoption and comprehension of artificial intelligence (AI) among assisted reproductive technology (ART) laboratory professionals?

DESIGN

A cross-sectional survey consisting of 32 questions was conducted among clinical embryologists worldwide using an online questionnaire between 17 July and 31 August 2023. The survey assessed familiarity with AI technology; current knowledge within laboratories; understanding of AI principles and limitations; and views on ethical concerns, job impacts and scientist-patient relationships.

RESULTS

In total, there were 702 survey respondents. The results revealed a high degree of awareness of AI concepts. The participants recognized the potential benefits of AI in embryology, but acknowledged known limitations. While open to the adoption of AI, they expressed reservations surrounding ethics, effects on jobs, and maintaining positive patient relationships. The study uncovered differences in embryologists' opinions based on their years of experience. Most embryologists, independent of age, were positive regarding AI, but workplace concerns diminished with age.

CONCLUSIONS

ART professionals are broadly receptive to AI, but ethical and practical uncertainties were raised. Further engagement between developers and end-users can align AI innovation with the values and needs of human practitioners.

A randomized controlled trial comparing embryo vitrification with slush nitrogen to liquid nitrogen in women undergoing frozen embryo transfer: embryology and clinical outcomes

STUDY QUESTION

Does the use of slush nitrogen (SN) for embryo vitrification improve embryo transfer outcomes compared to liquid nitrogen (LN)?

SUMMARY ANSWER

SN is a safe method for embryo preservation and significantly improves post-warming survival rates during repeated vitrification-warming cycles; however, after a single freeze-thaw cycle, pregnancy outcomes are not improved when embryos are vitrified with SN compared to LN.

WHAT IS KNOWN ALREADY

SN is a combination of solid and LN, with a temperature lower than regular LN, and it is an alternative to conventional LN in achieving a faster cooling speed. Studies have shown that SN improves survival in non-human embryos and human oocytes. However, it is unknown whether the use of SN reduces blastocyst damage in humans during vitrification-as indicated by increased survival across multiple vitrification-warming cycles-or whether it enhances pregnancy outcomes in a single vitrification-warming cycle.

STUDY DESIGN, SIZE, DURATION

Following the pre-clinical trial assessing embryo survival after repeated freeze-thaw cycles using SN and LN on 50 donated embryos per group, a randomized controlled trial was performed, where 253 patients were enrolled between September 2020 and January 2022, and 245 underwent an IVF stimulation, which resulted in at least one blastocyst for cryopreservation. Of those, 121 were allocated to the SN (study), and 124 were allocated to the LN (control) group. Randomization occurred on the day of blastocyst biopsy using a computer-generated block schema. Groups were assigned via opaque envelopes, opened by the embryologist on vitrification day. The patient, physician, and clinical team were blinded to the intervention.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All couples with female aged between 18 and 42 years old undergoing IVF stimulation at one university-affiliated infertility center, with plan for preimplantation genetic testing for aneuploidy and subsequent single, frozen embryo transfer (FET) were eligible for inclusion in this study.

MAIN RESULTS AND THE ROLE OF CHANCE

The pre-clinical trial demonstrated significant improvements in blastocyst survival, with the SN group achieving a mean of 7.5 survived vitrification-warming cycles (range: 3-22), significantly surpassing the mean of 3.0 cycles (range: 0-10) in the LN group (P < 0.0001). Following the pre-clinical trial, 223 patients randomized to SN or LN underwent single FET. Baseline characteristics were similar between groups, as were embryology outcomes, including the number of oocytes retrieved, mature oocytes, fertilization rate, and total blastocysts biopsied. No significant differences were observed between the two groups in pregnancy rate, clinical pregnancy rate, sustained implantation rate, or miscarriage rate (P = 0.16, 0.80, 0.49, and 0.74, respectively, using Student's t-test). A futility analysis indicated no value in continuing recruitment and therefore the study was closed.

LIMITATIONS, REASONS FOR CAUTION

Neonatal or birth outcomes were not assessed. Termination of the study based on futility analysis precludes a conclusion of equivalence between SN and LN.

WIDER IMPLICATIONS OF THE FINDINGS

This study demonstrates that SN is a safe alternative to traditional LN for vitrification; however, it did not demonstrate improvements in the reproductive potential of vitrified embryos.

STUDY FUNDING/COMPETING INTEREST(S)

The project was funded by the Foundation for Embryonic Competence.

TRIAL REGISTRATION NUMBER

NCT04496284.

TRIAL REGISTRATION DATE

3 August 2020.

DATE OF FIRST PATIENT’S ENROLLMENT

5 September 2020.

The effect of pipette- and laser-induced blastocyst collapse before vitrification on their re-expansion and clinical outcome after warming

RESEARCH QUESTION

What are the effects of pipette- versus laser-assisted artificial blastocyst collapse (ABC) on the morphokinetics of warmed blastocyst re-expansion, and what is the potential effect on treatment outcomes?

DESIGN

Surplus blastocysts were extracted from 203 patients. These were divided into three groups: study group A, artificial collapsed by the aspiration of blastocoel fluid with a pipette; study group B, trophectoderm opened with a laser pulse; control group, no manipulation before vitrification was performed. During the 5-year study period, 257 associated single-warm blastocyst transfers were scheduled. The start and duration of the re-expansion process before transfer were annotated. Pregnancy and live birth data were also collected for the transfers.

RESULTS

The overall blastocyst survival rate was 96.9%, with no effect observed as a result of the two ABC methods. The re-expansion of blastocysts in study group B was initiated significantly sooner after warming (0.50 ± 0.37 h) than in group A (0.79 ± 0.56 h) or the control group (1.22 ± 1.00 h). The duration of the re-expansion process was significantly reduced in study groups A (P = 0.021) and B (P = 0.004) compared with the control group. The embryos of participants who achieved a live birth had a significantly (P < 0.001) faster start of re-expansion (0.60 ± 0.42 h) than the embryos in those who did not produce an ongoing pregnancy (1.05 ± 0.92 h).

CONCLUSIONS

Laser-treated blastocysts exhibited substantially shorter re-expansion times. Because faster re-expansion of the blastocyst is associated with positive treatment outcomes, the laser technique should be prioritized over the pipetting technique if ABC is considered.

Best practices for cryopreserving sperm in Nonhuman Primates: a systematic review and meta-analysis

Nonhuman primates (NHPs) are in increasing demand as models for preclinical research. The availability of a highly efficient cryopreservation protocol for use with NHP sperm has potential to significantly alleviate this demand and contribute to rapid increases in overall number of NHPs available for biomedical research. Thus, this systematic review assesses the state-of-the-art in NHP sperm cryopreservation and uses meta-analyses to describe the impact of varied cryopreservation approaches on NHP sperm. We searched the literature deposited in PubMed, Scopus, and Web of Science databases through June 2024 to identify data relevant to the effect of sperm cryopreservation on quality of thawed sperm compared to fresh sperm across NHP species. All original NHP studies reporting sperm parameters both before cryopreservation and after thawing were included for analysis. In total, 32 articles were included for qualitative analysis and not surprisingly, all 32 studies demonstrated negative effects of cryopreservation on sperm parameters, Specifically, motility and viability were significantly decreased in thawed NHP sperm. While the method of sperm collection did not have a significant impact on recovery of motile sperm, significant variability was evident between species. Importantly, recovery of motile NHP sperm was greatest following rapid sperm freezing methods. This analysis provides critical insights into future research directions to enhance and optimize cryopreservation protocols in NHPs.

Oleanolic acid promotes porcine oocyte maturation by activating the Nrf2/HO-1 signalling pathway

This study investigated the potential role and underlying mechanisms of oleanolic acid (OA), a pentacyclic triterpene with antioxidant and anti-inflammatory properties, in porcine oocytes during in vitro maturation (IVM). The results showed that supplementation with 5 μM OA during IVM resulted in a greater percentage of mature oocytes, parthenogenetically activated embryos and somatic cell nuclear-transferred embryos. This was evidenced by significant increases in the rate of first polar body expulsion, the expansion of cumulus granulosa cells and the total cell number in blastocysts. Further analysis revealed that OA promoted fatty acid accumulation and upregulated the mRNA expression of genes involved in fatty acid β-oxidation. OA significantly increased the intracellular mitochondrial membrane potential and ATP levels and effectively inhibited BAX/BCL2 and Cleaved Caspase3 protein expression. Notably, OA increased the protein levels of intracellular Nrf2 and HO-1, and the GSH levels and the activities of the antioxidant enzymes SOD and catalase (CAT), while reducing ROS levels. Mechanistically, OA activated the Nrf2/HO-1 signalling pathway, which is crucial for regulating the expression of antioxidant-related targets in IVM porcine oocytes. Our findings indicated that OA improved antioxidant capacity by activating the Nrf2/HO-1 signalling pathway, thereby promoting porcine oocyte maturation.

Molecular mechanisms of natural antifreeze phenomena and their application in cryopreservation

Cryopreservation presents a critical challenge due to cryo-damage, such as crystallization and osmotic imbalances that compromise the integrity of biological tissues and cells. In contrast, various organisms in nature exhibit remarkable freezing tolerance, leveraging complex molecular mechanisms to survive extreme cold. This review explores the adaptive strategies of freeze-tolerant species, including the regulation of specific genes, proteins, and metabolic pathways, to enhance survival in low-temperature environments. We then discuss recent advancements in cryopreservation technologies that aim to mimic these natural phenomena to preserve cellular and tissue integrity. Special focus is given to the roles of glucose metabolism, microRNA expression, and cryoprotective protein modulation in improving cryopreservation outcomes. The insights gained from studying natural antifreeze mechanisms offer promising directions for advancing cryopreservation techniques, with potential applications in medical, agricultural, and conservation fields. Future research should aim to further elucidate these molecular mechanisms to develop more effective and reliable cryopreservation methods.

Endometriotic tissue fragments are viable after cryopreservation in an ex vivo tissue model recapitulating the fibrotic microenvironment

STUDY QUESTION

Is it possible to establish an ex vivo endometriosis model using cryopreserved endometriotic tissue fragments?

SUMMARY ANSWER

Cryopreserved endometriotic tissue fragments remain viable after thawing and during at least 3 days of culture and can therefore be used to establish an ex vivo endometriosis model to efficiently test potential therapeutic agents.

WHAT IS KNOWN ALREADY

Endometriosis is the most prevalent benign gynecologic disease with an enormous societal burden; however, curative therapies are still lacking. To efficiently test potential new therapies, an ex vivo model based on previously cryopreserved endometriotic tissue that recapitulates the different endometriosis subtypes and their microenvironment is highly desirable.

STUDY DESIGN, SIZE, DURATION

Endometriotic tissue fragments of three different subtypes were obtained from 28 patients by surgical resection. After cryopreservation and thawing, viability and metabolic activity of these tissue fragments were assessed. Viability was compared with fresh fragments from 11 patients directly after surgical removal. Experimental intervention studies were performed in cryopreserved and thawed tissue fragments from two patients to confirm the usability of these tissues for ex vivo intervention studies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometriotic tissue fragments (n = 45) were cryopreserved according to three different protocols. After thawing, fragments were cultured for 24 h. A resazurin-based assay was performed to assess the metabolic activity of the tissue fragments. In addition, cell type-specific viability was analyzed by VivaFix, Hoechst 33342, and α-smooth muscle actin immunofluorescence staining and confocal microscopy. The presence of endometriosis was histologically confirmed based on hematoxylin-eosin staining. Cryopreserved and thawed tissue fragments were treated for 72 h with pirfenidone or metformin and COL1A1 and CEMIP gene expressions were assessed using RT-PCR and RT-qPCR, either in the whole tissue fragments or in myofibroblasts isolated by laser capture microdissection.

MAIN RESULTS AND THE ROLE OF CHANCE

Metabolic activity of endometriotic tissue fragments obtained from peritoneal (PER), ovarian (OMA), and deep (DE) endometriotic lesions was well preserved after cryopreservation in a dimethyl sulfoxide-based medium and was comparable with fresh tissue fragments. Relative metabolic activity compared to fresh tissue was 70% (CI: 92-47%) in PER, 43% (CI: 53-15%) in OMA and 94% (CI: 186-3%) in DE lesions. In fragments from PE lesions 92% (CI: 87-96%), from OMA lesions 95% (CI: 91-98%), and from DE lesions 88% (CI: 78-98%) of cells were viable after cryopreservation and thawing followed by a 24-h culture period. Differences in gene expression of fibrotic markers COL1A1 and CEMIP after 72-h treatment with pirfenidone or metformin could be detected in whole tissue fragments and in isolated myofibroblasts, indicating that cryopreserved and thawed endometriotic tissue fragments are suitable for testing anti-fibrotic interventions.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Viability and metabolic activity of the endometriotic tissue fragments may have been partially compromised by damage sustained during the surgical procedure, contributing to inter-sample variance.

WIDER IMPLICATIONS OF THE FINDINGS

The storage of viable endometriotic tissue fragments for later usage in an ex vivo model creates the possibility to efficiently test potential new therapeutic strategies and facilitates the exchange of viable endometriotic tissue between different research laboratories.

STUDY FUNDING/COMPETING INTEREST(S)

This study was not financially supported by external funding. The authors declare no competing interest.

TRIAL REGISTRATION NUMBER

N/A.

Cohort differences between preschool development of in vitro fertilization and naturally conceived infants

To explore the differential cohort situation between preschool development of in vitro fertilization (IVF) and naturally conceived infants. From April 2014 to June 2022, 60 preschool IVFs were selected as the research subjects for follow-up at the pediatric health clinic of hospital's prevention and health department. They were set as the experimental group (Group S), and 60 naturally conceived infants of the same age were selected as the control group (Group Z). Data from both groups were collected through telephone follow-up and other methods. No significant difference showed between the 2 groups in age specific height, age specific weight, Gesell developmental score, Denver developmental screening test screening results, intellectual development index, and motor development index (P > .05). The influence of birth environment factors such as family background and maternal education level on children's height and weight was not significant (P > .05), while maternal education level had a significant impact on children's intellectual development index (P < .05). No significant difference showed in the development of preschool children in IVF compared to naturally conceived children, and the level of parental education has a significant impact on children's mental and motor development.

Fertility preservation in women with endometriosis: Oocyte cryopreservation and other techniques

In recent years, advancements in cryopreservation techniques for oocytes, embryos, and ovarian tissue have enabled offering fertility preservation (FP) options to women with endometriosis. It is recommended to always conduct specialized counselling on FP, especially before considering surgical interventions for endometriosis. The decision regarding the methods of FP, the timing, and to which women affected by endometriosis these techniques should be offered are still subjects of discussion. However, several studies suggest that it can be proposed before surgical interventions for endometriosis, particularly if the patient is undergoing mono or bilateral endometrioma surgery. The most recommended technique is ovarian stimulation, followed by oocyte cryopreservation. Nevertheless, the literature contains various studies describing FP through embryo cryopreservation or the retrieval and cryopreservation of ovarian tissue.