The effect of extended cryo-storage following vitrification on embryo competence: a systematic review and meta-analysis

Assessing the effect of below-benchmark vitrified/warmed donor-oocyte survival rates in subsequent laboratory and clinical outcomes

OBJECTIVE

To assess the impact of below-benchmark (95%-100%) donor-oocyte survival rates on vitrification/warming in the laboratory and clinical outcomes of recipient cycles.

DESIGN

Retrospective cohort study.

SUBJECTS

We analyzed 12,690 vitrified-warmed donor-oocyte recipient cycles performed from 2018-2022.

EXPOSURE

All cycles analyzed used exclusively vitrified/warmed donor oocytes. The cycles were grouped according to the survival rate experienced: benchmark 95%-100%; competence 85%-95%; below competence 70%-85%; poor 50%-70%; and very poor <50%.

MAIN OUTCOME MEASURES

The primary endpoint of the study was the total usable blastocyst rate per 2 pronuclear (2PN) zygote. Secondary endpoints were the fertilization rate, the live birth rate after the first single blastocyst transfer, and the cumulative live birth rate.

RESULTS

The mean number of warmed oocytes per intracytoplasmic sperm injection (ICSI) cycle was 11.4 ± 3.2, with a mean survival rate of 89.1%. More oocytes per cycle were consumed in the lower survival groups, yet the total number of oocytes available for ICSI was smaller in the below-competence, poor, and very poor survival groups. The total usable blastocyst rate was lower in the lower survival groups (benchmark: 48.9%; competence: 47.0%, below competence: 46.0%; poor: 43.6%; and very poor: 43.6%), as well as the fertilization rates (benchmark: 76.8%; competence: 76.6%, below competence: 75.6%; poor: 74.7%; and very poor:75.5%). The adjusted relative risk (aRR) of live birth rate of the first embryo transferred was equal to the benchmark survival group in all the lower survival groups (benchmark: 40.9%; competence: aRR = 0.986, 95% confidence interval [CI]: 0.931-1.045; below-competence: aRR = 0.992, 95% CI: 0.929-1.059; poor: aRR = 1.103, 95% CI: 1.009-1.207; and very poor: aRR = 1.169, 95% CI: 0.963-1.419). The cumulative live birth rate decreased in lower survival groups compared with benchmark survival (benchmark: 79.2%; competence: aRR = 0.988, 95% CI: 0.961-1.015; below competence: aRR = 0.911, 95% CI: 0.880-0.944; poor: aRR = 0.802, 95% CI: 0.757-0.851; and very poor: aRR = 0.793, 95% CI: 0.693-0.907). The lower cumulative rates maintained in a subanalysis with equal metaphase-II available for ICSI (benchmark: 69.5%; competence: aRR = 0.909, 95% CI: 0.827-1.000; below competence: aRR = 0.942, 95% CI: 0.848-1.046; poor: aRR = 0.833, 95% CI: 0.7386-0.941; and very poor: aRR = 0.873, 95% CI: 0.695-1.097) CONCLUSION: Lower donor-oocyte cryo-survival rates have a moderate negative impact on the blastocyst utilization rate per 2PN zygote, fertilization rate, and the cumulative live birth rates of a donation cycle, even after adjusting for equal metaphase-II oocytes available for ICSI. Nonetheless, the surviving oocytes of a cohort seem to maintain a high competence level, with very similar laboratory outcomes, irrespective of the cohort's survival rates, as well as equal implantation potential of the resulting blastocysts.

Patient-specific predictors of successful frozen embryo transfer using the freeze-all protocol: a retrospective observational study

BACKGROUND

The aim of this study was to examine various patient factors affecting first programmed embryo transfer (ET) outcomes under the freeze-all policy at a single tertiary university infertility center.

METHODS

This retrospective observational study reviewed the medical records of 243 couples who underwent their first ET using blastocysts collected under the freeze-all antagonist-controlled ovarian stimulation (COS) protocol from 2015 to 2023. Patients were grouped into pregnant and nonpregnant groups, and their data, including demographics, COS and ET outcomes, and embryo storage duration, were analyzed.

RESULTS

Patient body mass index, cause of infertility, follicle-to-oocyte index, distribution of blastocyst grades, number of transferred embryos, and embryo storage duration were not significantly different between the groups. In a simple comparative analysis, patients with successful clinical pregnancy tended to have significantly lower female and male age (33.83±3.67 and 35.32±4.54 years vs. 37.07±4.15 and 39.33±5.60 years, respectively), higher anti-Müllerian hormone levels (6.27±5.32 ng/mL vs. 4.14±3.82 ng/mL) and antral follicle counts (14.20±8.26 vs. 10.04±5.75), and higher numbers of retrieved oocytes and metaphase II oocytes (13.74±6.92 and 9.64±6.19 vs. 11.21±6.04 and 7.53±5.56, respectively). Multivariate logistic regression analysis of these variables revealed that only male age was a significant factor for successful clinical pregnancy (odds ratio, 4.768; 95% confidence interval, 1.252-18.162; p=0.022).

CONCLUSION

During the first programmed ET using blastocysts collected under the freeze-all antagonist COS protocol, male age and correspondingly the quality of gametes for fertilization were crucial for successful pregnancy, having more importance than calculated female ovarian reserve and embryo storage duration.

Beyond the icebox: modern strategies in organ preservation for transplantation

Organ transplantation, a critical treatment for end-stage organ failure, has witnessed significant advancements due to the integration of improved surgical techniques, immunosuppressive therapies, and donor-recipient matching. This review explores the progress of organ preservation, focusing on the shift from static cold storage (SCS) to advanced machine perfusion techniques such as hypothermic (HMP) and normothermic machine perfusion (NMP). Although SCS has been the standard approach, its limitations in preserving marginal organs and preventing ischemia-reperfusion injury (IRI) have led to the adoption of HMP and NMP. HMP, which is now the gold standard for high-risk donor kidneys, reduces metabolic activity and improves posttransplant outcomes. NMP allows real-time organ viability assessment and reconditioning, especially for liver transplants. Controlled oxygenated rewarming further minimizes IRI by addressing mitochondrial dysfunction. The review also highlights the potential of cryopreservation for long-term organ storage, despite challenges with ice formation. These advances are crucial for expanding the donor pool, improving transplant success rates, and addressing organ shortages. Continued innovation is necessary to meet the growing demands of transplantation and save more lives.

Impact of prolonged embryo storage on reproductive and neonatal outcomes: a systematic review and meta-analysis

PURPOSE

To analyze the influence of embryo storage on reproductive and neonatal results in patients undergoing in vitro fertilization (IVF) treatment.

METHODS

PubMed, Embase, Cochrane Central Register of Controlled Trials, and BioMed Central databases were searched from inception up to June 2024 for studies comparing reproductive and neonatal outcomes in patients undergoing frozen embryo transfer within 12 months from embryo storage versus more than 12 months after embryo storage. Data were pooled by meta-analysis using a random effects model.

RESULTS

A total of 16 studies, involving 233,315 embryos were included. Patients undergoing frozen embryo within 12 months from embryo storage were associated with higher rates of live birth (OR 1.17, 95% CI 1.09-1.26, I2 = 78%) biochemical pregnancy (OR 1.26, 95% CI 1.08-1.47, I2 = 77.8%) clinical pregnancy (OR 1.24, 95% CI 1.12-1.38, I2 = 86.3%) and multiple pregnancy rate (OR 1.26, 95% CI 1.03-1.55, I2 = 69%). No significant differences between groups were shown in terms of survival rate (OR 1.52, 95% CI 0.65-3.58, I2 = 98.5%), miscarriage (OR 1.08, 95% CI 0.91-1.27, I2 = 77%), implantation rate (OR 1.17, 95% CI 0.90-1.52, I2 = 91.7%) and ectopic pregnancy (OR 0.98, 95% CI 0.80-1.20, I2 = 0%). In addition, prolonged embryo storage was not associated with higher rates of preterm delivery (OR 0.86, 95% CI 0.67-1.09, I2 = 8.3%), low weight at birth (OR 1.10, 95% CI 0.88-1.38, I2 = 24.3%) or congenital malformations (OR 0.90, 95% CI 0.65-1.25, I2 = 0.8%).

CONCLUSION

Prolonged embryo storage over 12 months is associated with lower rates of live birth, biochemical pregnancy, clinical pregnancy, and multiple pregnancy. However, important covariates such as reasons for delay of transfer, embryo quality, and improper handling of embryos could not be ruled out as causes of this reduction. Given these limitations, these conclusions should be viewed with caution.

Embryo long-term storage does not affect assisted reproductive technologies outcome: analysis of 58,001 vitrified blastocysts over 11 years

BACKGROUND

Recently, the potential detrimental effect that the duration of storage time may have on vitrified samples has raised some concerns, especially when some studies found an association between cryostorage length and decreased clinical results.

OBJECTIVE

This study aimed to evaluate the effects of the storage time length of day-5 vitrified blastocysts in 2 study groups: freeze-all cycles and nonelective frozen embryo transfers.

STUDY DESIGN

This was a retrospective study that included 58,001 vitrified/warmed day-5 blastocysts from 2 different populations, according to the reason for frozen embryo transfer. Elective frozen embryo transfer comprised freeze-all cycles (N=16,615 blastocysts and 16,615 patients) in which only single embryo transfers and only the first frozen embryo transfer were included. The nonelective frozen embryo transfer group included 41,386 embryos from 25,571 patients where frozen embryo transfer took place using supernumerary embryos after fresh embryo transfer. All the possible frozen embryo transfers were included. Both single embryo transfer and double embryo transfers were included. Donor and autologous oocytes were used. The period covered by this study was 11 years. The blastocyst sample was clustered into deciles, which provided specific storage duration categories. The main outcome was the live birth rate, and secondary outcomes were embryo survival, miscarriage, and clinical and ongoing pregnancy rates according to storage duration. The impact of storage time was assessed by univariable analyses in both groups. The comparison was made between each decile and the last one. A multivariable logistic regression analysis was conducted, including the variables with significant association found in the univariate analysis. Student t test and chi-square tests, or an analysis of variance, were used wherever appropriate. P<.05 was considered statistically significant.

RESULTS

There were statistical differences in baseline characteristics of patients included in the study groups. Storage durations ranged from ≤0.67 to ≥4.34 and from ≤1.8 to ≥34.81 months in freeze-all and nonelective frozen embryo transfer, respectively. Embryo survival did not show statistical differences across the categories of storage time in freeze-all and nonelective frozen embryo transfer groups. Statistical differences were found for the live birth rate across some, but not all, the subgroups of storage duration. The multivariable analysis showed no association between storage time and the live birth rate in both groups (nonsignificant). Blastocyst quality, body mass index, number of retrieved oocytes, endometrial preparation, male factor, and uterine factor were related to the drop in the live birth rate in the freeze-all group (P<.05). In the nonelective frozen embryo transfer group, the variables that showed significant association with the live birth rate were age at retrieval and frozen embryo transfer, type of frozen embryo transfer (single embryo transfer or double embryo transfers), number of retrieved oocytes, body mass index, endometrial preparation, origin of sperm sample, and female factor.

CONCLUSION

This large study demonstrated no association between storage time and clinical outcome. Other variables, such as the patient's age, embryo quality, body mass index, and etiology, are somewhat responsible for impacting the outcome. This provides evidence for the safety of embryo vitrification, even after long storage periods. This is reassuring for both in vitro fertilization practitioners and patients undergoing frozen embryo transfer of either elective or nonelective embryos.

Embryo transfer impact: a comprehensive national cohort analysis comparing maternal and neonatal outcomes across varied embryo stages in fresh and frozen transfers

Introduction

The utilization of frozen embryo transfer not only enhances reproductive outcomes by elevating the likelihood of live birth and clinical pregnancy but also improves safety by mitigating the risks associated with ovarian hyperstimulation syndrome (OHSS) and multiple pregnancies. There has been an increasing debate in recent years regarding the advisability of making elective frozen embryo transfer the standard practice. Our study aims to determine the optimal choice between fresh and frozen embryo transfer, as well as whether the transfer should occur at the cleavage or blastocyst stage.

Method

In this retrospective cohort study conducted in Taiwan, data from the national assisted reproductive technology (ART) database spanning from January 1st, 2013, to December 31st, 2017, were analyzed. The study included 51,762 eligible female participants who underwent ART and embryo transfer. Pregnancy outcomes, maternal complications, and singleton neonatal outcomes were evaluated using the National Health Insurance Database from January 1st, 2013, to December 31st, 2018. Cases were categorized into groups based on whether they underwent fresh or frozen embryo transfers, with further subdivision into cleavage stage and blastocyst stage transfers. Exposure variables encompassed clinical pregnancy rate, live birth rate, OHSS, pregnancy-induced hypertension, gestational diabetes mellitus (DM), placenta previa, placental abruption, preterm premature rupture of membranes (PPROM), gestational age, newborn body weight, and route of delivery.

Results

Frozen blastocyst transfers showed higher rates of clinical pregnancy (CPR) and live births (LBR) compared to fresh blastocyst transfers. Conversely, frozen cleavage stage transfers demonstrated lower rates of clinical pregnancy and live birth compared to fresh cleavage stage transfers. Frozen embryo transfers were associated with reduced risks of OHSS but were linked to a higher risk of pregnancy-induced hypertension compared to fresh embryo transfers. Additionally, frozen embryo transfers were associated with a higher incidence of large for gestational age infants and a lower incidence of small for gestational age infants.

Conclusion

The freeze-all strategy may not be suitable for universal application. When embryos can develop to the blastocyst stage, FET is a favorable choice, but embryos can only develop to the cleavage stage, fresh embryo transfer becomes a more reasonable option.

Innovative Strategies for Fertility Preservation in Female Cancer Survivors: New Hope from Artificial Ovary Construction and Stem Cell-Derived Neo-Folliculogenesis

Recent advances in anticancer treatment have significantly improved the survival rate of young females; unfortunately, in about one third of cancer survivors the risk of ovarian insufficiency and infertility is still quite relevant. As the possibility of becoming a mother after recovery from a juvenile cancer is an important part of the quality of life, several procedures to preserve fertility have been developed: ovarian surgical transposition, induction of ovarian quiescence by gonadotropin-releasing hormone agonists (GnRH-a) treatment, and oocyte and/or ovarian cortical tissue cryopreservation. Ovarian tissue cryostorage and allografting is a valuable technique that applies even to prepubertal girls; however, some patients cannot benefit from it due to the high risk of reintroducing cancer cells during allograft in cases of ovary-metastasizing neoplasias, such as leukemias or NH lymphomas. Innovative techniques are now under investigation, as in the construction of an artificial ovary made of isolated follicles inserted into an artificial matrix scaffold, and the use of stem cells, including ovarian stem cells (OSCs), to obtain neo-folliculogenesis and the development of fertilizable oocytes from the exhausted ovarian tissue. This review synthesizes and discusses these innovative techniques, which potentially represent interesting strategies in oncofertility programs and a new hope for young female cancer survivors.

Cryostorage management of reproductive cells and tissues in ART: status, needs, opportunities and potential new challenges

Among the wide range of procedures performed by clinical embryologists, the cryopreservation of reproductive cells and tissues represents a fundamental task in the daily routine. Indeed, cryopreservation procedures can be considered a subspecialty of medically assisted reproductive technology (ART), having the same relevance as sperm injection or embryo biopsy for preimplantation genetic testing. However, although a great deal of care has been devoted to optimizing cryopreservation protocols, the same energy has only recently been spent on developing and implementing strategies for the safe and reliable storage and transport of reproductive specimens. Herein, we have summarized the content of the available guidelines, the risks, the needs and the future perspectives regarding the management of cryopreservation biorepositories used in ART.

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

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

Effect of exposed-to-air frequency of cryopreserved embryo on clinical outcomes of vitrified-warmed embryo transfer cycles: a retrospective analysis of 9,200 vitrified-warmed transfer cycles

BACKGROUND

Cryopreservation of embryos plays a major role in the in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) treatment. However, the storage condition of the cryopreserved embryo can change temporarily due to repeated retrieval of the embryo from the liquid nitrogen (LN2) tank during the practical application during cryopreservation. Whether the implantation potential of a cryopreserved embryo will be damaged when the cane containing it is temporarily exposed to air due to the transfer between the LN2 tank and LN2 container is yet to be elucidated. Also, whether the exposed-to-air frequency (EAF) of cryopreserved embryos influences the clinical outcomes is unclear.

OBJECTIVE

To investigate whether the EAF of cryopreserved embryo affects the clinical outcomes of vitrified-warmed embryo transfer.

METHODS

A total of 9200 vitrified-warmed embryo transfer cycles were included in this study. All cycles were divided into five groups according to different EAFs (2, 4, 6, 8, or ≥ 10). Post-warming survival rates and clinical outcomes, including implantation, clinical pregnancy and live birth rates were investigated. Kruskal-Wallis test and Pearson's chi-squared tests were used to compare the patient characteristics and clinical outcomes among the five groups. Furthermore, multivariate logistic regression analyses were conducted to investigate the association between EAF and clinical outcomes.

RESULTS

No significant differences were observed in the positive HCG rate, implantation rate and live birth rate (P > 0.05) among five EAF groups with respect to D3 embryo, D5 blastocyst and D6 blastocyst. Post-warmed survival rate of D3 embryos (P = 0.015) differed significantly among the five EAF groups, but it was not EAF-dependent. Although clinical pregnancy was different among the five groups with respect to D5 blastocyst (P = 0.042), multivariate logistic regression analysis adjusted for confounding variables suggested that EAF did not adversely affect clinical pregnancy or live birth.

CONCLUSION

These findings indicated that human vitrified embryos in the open system could be repeatedly retrieved from the LN2 tank without affecting the implantation potential of the embryo.

Storage duration of vitrified embryos does not affect pregnancy and neonatal outcomes after frozen-thawed embryo transfer

Background

With the refinement of cryopreservation technology, the number of frozen-warmed embryo transfer (FET) cycles and cryopreserved embryos has increased rapidly. However, studies investigating the effect of storage duration on pregnancy outcomes after vitrification are limited and their results are controversial. Furthermore, the available studies did not take patients' demographic nor clinical treatment characteristics into account and the cryo-storage duration was short. So this study aimed to explore the effect of storage duration of vitrified warmed embryos on pregnancy and neonatal outcomes in patients with good prognosis and long storage duration of vitrified embryos.

Methods

This study was a bi-centre, retrospective study including 1037 women undergoing their first FET cycles following a fresh cycle from January 2012 until December 2021. Patients were divided into four storage groups in accordance with the storage duration of transferred embryos (612 patients in group I, with storage duration between 1 and 6 months; 202 patients in group II, with storage duration between 7 and 12 months; 141 patients in group III, with storage duration between 13 and 36 months; and 76 patients in group IV, with storage duration between 37 and 84 months). The pregnancy and neonatal outcomes were compared amongst different storage duration groups.

Results

Amongst the different groups, no significant differences were observed in the pregnancy outcomes, including biochemical pregnancy rate, implantation rate, clinical pregnancy rate, ongoing pregnancy rate and live birth rate. In addition, no evidence of differences amongst different storage duration groups was observed in terms of preterm birth, birth length and low birthweight.

Conclusions

The pregnancy and neonatal outcomes of embryos after vitrification were not impaired by storage duration up to 7 years.

Prolong cryopreservation duration negatively affects pregnancy outcomes of vitrified-warmed blastocyst transfers using an open-device system: A retrospective cohort study

OBJECTIVE

To investigate the impact of cryopreservation (CP) duration on pregnancy outcomes of vitrified-warmed blastocysts transfers using an open-device liquid-nitrogen (LN₂) system.

METHODS

This retrospective cohort study was conducted on 6327 first vitrified-warmed single blastocyst transfer cycles with autologous oocytes from January 2015 to December 2020. The CP duration was initially divided into six groups: Group I: 0-3 months (n = 4309); Group II: 4-6 months (n = 1061); Group III: 7-12 months (n = 304); Group IV: 13-24 months (n = 113); Group V: 25-72 months (n = 466); Group VI: 73-120 months (n = 74). Multivariate logistic regression was performed to evaluate the independent effect of CP duration on pregnancy outcomes. To further examine the time limit of vitrification, propensity score matching (PSM) was applied to compare pregnancy outcome of patients with storage duration of 25-120 months to those of 0-24 months. After that, pregnancy outcomes were compared among the subgroups of Group I': 0-24 months, Group II': 25-48 months, Group III': 49-72 months, Group IV': 73-120 months. Stratification analysis based on embryo quality was also performed. Primary outcomes were clinical pregnancy rate and live birth rate. Secondary outcomes were implantation, biochemical pregnancy rate, ongoing pregnancy rate and early miscarriage rate.

RESULTS

Logistic regression demonstrated that the odds of pregnancy outcomes were similar across Group I to IV. However, the implantation rate, chances of biochemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth significantly decreased as the storage duration increased up to 25 months, while miscarriage rate did not significantly differ between groups. Subgroup analysis confirmed a dramatical decrease of clinical pregnancy and live birth rate when cryopreserved for more than 24 months. After that, the slope was relatively steady between 25 and 72 months, then steeply decreased again as CP reached 73-120 months. In addition, there was a more remarkable decline of pregnancy outcomes in the average quality embryo transfers than in the high quality embryo transfers as cryopreservation storage increased.

CONCLUSION

Prolonged cryopreservation of vitrified blastocysts in an open-device LN₂ system up to 24 months might negatively affect pregnancy outcomes. This negative impact progresses as storage duration increases, especially when exceeds 72 months. Average quality embryo appears to be less sustainable with long-term cryo-storage.

Effects of vitrified cryopreservation duration on IVF and neonatal outcomes

Background

In this study, we aimed to evaluate the impact of the duration of cryopreservation storage on embryo viability, implantation competence, pregnancy outcome and neonatal outcomes.

Methods

We retrospectively evaluated the outcomes of patients who underwent IVF with vitrified cryopreserved embryos between January 2004 and August 2019 by following the first frozen embryo transfer cycles within the study period. A total of 31,143 patients met the inclusion criteria and were grouped according to the embryo storage time as follows: Group 1 (n = 20,926),1–90 days; Group 2 (n = 6,472), 91–180 days; Group 3 (n = 2,237), 181–365 days; Group 4 (n = 746), 366–730 days; and Group 5 (n = 762), > 731 days.

Results

The embryo survival rate decreased significantly with longer durations of cryopreservation. The highest and lowest survival rate was recorded in Group 1 and Group 5, respectively (34853/35338; 98.63% vs. 1281/1801; 71.13%; P < 0.01). The human chorionic gonadotropin (HCG) detection and clinical pregnancy rate was highest in Group 1 (57.85% and 55. 26%, respectively; P < 0.01). Short-term cryopreservation (≤ 3 months) is associated with higher rates of clinical pregnancy. There were no significant differences in neonatal birth weight, neonatal height and congenital anomalies among the groups (P > 0. 05).

Conclusion

The prolonged storage time of vitrified embryos negatively affected survival rate and clinical pregnancy rate. It did not have a significant influence on neonatal health. This study provides new findings about the relationship between prolonged storage time of vitrified embryos and clinical outcomes and offers evidence for the safety of using long-stored embryos after vitrification.