Cryostorage duration does not affect pregnancy and neonatal outcomes: a retrospective single-centre cohort study of vitrified–warmed blastocysts

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.

Vitrification preservation of good-quality blastocysts for more than 5 years reduces implantation and live birth rates

STUDY QUESTION

Does vitrification cryopreservation of embryos for more than 5 years affect the pregnancy outcomes after frozen embryo transfer (FET)?

SUMMARY ANSWER

Vitrification cryopreservation of good-quality blastocysts for more than 5 years is associated with a decrease in the implantation rate (IR) and live birth rate (LBR).

WHAT IS KNOWN ALREADY

Previous studies have predominantly focused on embryos cryopreserved for relatively short durations (less than 5 years), yet the impact of extended cryopreservation duration on pregnancy outcomes remains a controversial issue. There is a relative scarcity of data regarding the efficacy and safety of storing embryos for 5 years or longer.

STUDY DESIGN, SIZE, DURATION

This retrospective study involved 36 665 eligible vitrified-thawed embryo transfer cycles from 1 January 2016 to 31 December 2022, at a single fertility center in China.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were divided into three groups according to embryo storage time: Group 1 consisted of 31 565 cycles, with storage time of 0-2 years; Group 2 consisted of 4458 cycles, with a storage time of 2-5 years; and Group 3 included 642 cycles, with storage time exceeding 5 years. The main outcome measures were IR and LBR. Secondary outcome variables included rates of biochemical pregnancy, multiple pregnancy, ectopic pregnancy, and miscarriage, as well as neonatal outcomes. Reproductive outcomes were analyzed as binary variables. Multivariate logistic regression analysis was used to explore the effect of preservation time on pregnancy outcomes after correcting for confounding factors. In addition, we also assessed neonatal outcomes, such as large for gestational age (LGA) and small for gestational age (SGA).

MAIN RESULTS AND THE ROLE OF CHANCE

IRs in the three groups (0-2, 2-5, and >5 years) were 37.37%, 39.03%, and 35.78%, respectively (P = 0.017), and LBRs in the three groups were 37.29%, 39.09%, and 34.91%, respectively (P = 0.028). After adjustment for potential confounding factors, compared with the 0-2 years storage group, prolonged embryo vitrification preservation time (2-5 years or >5 years) did not affect secondary outcomes such as rates of biochemical pregnancy, multiple pregnancy, ectopic pregnancy, and miscarriage (P > 0.05). But cryopreservation of embryos for more than 5 years reduced the IR (adjusted odds ratio (aOR) 0.82, 95% CI 0.69-0.97, P = 0.020) and LBR (aOR 0.76, 95% CI 0.64-0.91, P = 0.002). Multivariate stratified analysis also showed that prolonging the cryopreservation time of blastocysts (>5 years) reduced the IR (aOR 0.78, 95% CI 0.62-0.98, P = 0.033) and LBR (aOR 0.68, 95% CI 0.53-0.87, P = 0.002). However, no effect on cleavage embryos was observed (P > 0.05). We further conducted stratified analyses based on the number and quality of frozen blastocysts transferred, and the results showed that the FET results after transfers of good-quality blastocysts in the >5 years storage group were negatively affected. However, the storage time of non-good-quality blastocysts was not significantly associated with pregnancy outcomes. Regarding the neonatal outcomes (of singletons), embryo vitrification preservation time had no effect on preterm birth rates, fetal birth weight, or neonatal sex ratios. However, as the storage time increased, rates of SGA (5.60%, 4.10%, and 1.18%) decreased, while rates of LGA (5.22%, 6.75%, and 9.47%) increased (P < 0.05). After adjusting for confounding factors, the increase in LGA and the decrease in SGA were significantly correlated with the duration of storage time.

LIMITATIONS, REASONS FOR CAUTION

This was a retrospective study using data from a single fertility center, even though the data had been adjusted, our findings still need to be validated in further studies.

WIDER IMPLICATIONS OF THE FINDINGS

With the full implementation of the two-child policy in China, there may be more patients whose embryos have been frozen for a longer time in the future. Patients should be aware that the IR and LBR of blastocysts are negatively affected when the cryopreservation time is longer than 5 years. Couples may therefore consider shortening the time until FET treatment.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Nature Science Foundation of China (No. 82101672), Science and Technology Projects in Guangzhou (No. 2024A03J0180), General Guidance Program for Western Medicine of Guangzhou Municipal Health Commission (No. 20231A011096), and the Medical Key Discipline of Guangzhou (2021-2023). None of the authors have any conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

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.

Effect of post-vitrification cryopreservation duration on singleton birth-weight in frozen-thawed blastocysts transfer cycles

Introduction

This study aimed to explore the effect of cryopreservation duration after blastocyst vitrification on the singleton birth-weight of newborns to assess the safety of long-term preservation of frozen-thawed blastocyst transfer (FBT) cycles.

Methods

This was a retrospective observational study conducted at the Gynecological Endocrinology and Assisted Reproduction Center of the Peking Union Medical College Hospital. Patients who gave birth to singletons between January 2006 and December 2021 after undergoing FBT cycles were included. Five groups were formed according to the duration of cryopreservation of embryos at FBT: Group I included 274 patients with a storage time < 3 months. Group II included 607 patients with a storage time of 3-6 months. Group III included 322 patients with a storage time of 6-12 months. Group IV included 190 patients with a storage time of 12-24 months. Group V included 118 patients with a storage time of > 24 months. Neonatal outcomes were compared among the groups. Multivariate linear regression analysis was performed to evaluate birth-weights and other birth-related outcomes.

Results

A total of 1,511 patients were included in the analysis. The longest cryopreservation period was 12 years. The birth-weights of neonates in the five groups were 3344.1 ± 529.3, 3326.1 ± 565.7, 3260.3 ± 584.1, 3349.9 ± 582.7, and 3296.7 ± 491.9 g, respectively (P > 0.05). The incidences of preterm birth, very preterm birth, low birth-weight, and very low birth-weight were similar in all groups (P > 0.05). The large-for-gestational-age and small-for-gestational-age rates did not differ significantly among the groups (P > 0.05). After adjusting for confounding factors that may affect neonatal outcomes, a trend for an increased risk of low birth-weight with prolonged cryopreservation was observed. However, cryopreservation duration and neonatal birth-weight were not significantly correlated (P > 0.05).

Conclusion

The duration of cryopreservation after blastocyst vitrification with an open device for more than 2 years had no significant effect on the birth-weight of FBT singletons; however, attention should be paid to a possible increase in the risk of low birth-weight.

Storage time does not influence pregnancy and neonatal outcomes for first single vitrified high-quality blastocyst transfer cycle

RESEARCH QUESTION

Does blastocyst storage time have an impact on pregnancy and neonatal outcomes following the first single vitrified/warmed high-quality blastocyst transfer cycle for young women?

DESIGN

Retrospective cohort study in a university-affiliated reproductive medical centre.

RESULTS

A total of 2938 patients undergoing their first frozen embryo transfer (FET) cycle with a single high-quality blastocyst (Day 5: 3BB and above; Day 6: 4BB and above) transferred were divided into five groups: Group A with storage time ≤3 months (n = 1621), Group B with storage time of 4-6 months (n = 657), Group C with storage time of 7-12 months (n = 225), Group D with storage time of 13-24 months (n = 104), and Group E with storage time of 25-98 months (n = 331). After adjusting for confounding factors by multivariate logistic regression, there were no significant differences in live birth rate [Group A as reference; Group B: adjusted odds ratio (aOR) 0.954 (95% CI 0.791- 1.151); Group C: aOR 0.905 (95% CI 0.674-1.214); Group D: aOR 0.727 (95% CI 0.474-1.114); Group E: aOR 1.185 (955 CI 0.873-1.608)], β-human-chorionic-gonadotropin-positive rate, clinical pregnancy rate and miscarriage rate between Group A and the other groups. Among all singletons born after FET, there were no significant differences with regards to gestational age, preterm birth, birthweight, low birthweight, high birthweight and macrosomia.

CONCLUSION

Long-term cryostorage of human vitrified high-quality blastocysts does not affect pregnancy or neonatal outcomes.

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.

Pregnancy and neonatal outcomes after long-term vitrification of blastocysts among 6,900 patients after their last live birth

OBJECTIVE

To evaluate whether prolonged storage of vitrified blastocysts negatively impacts pregnancy and neonatal outcomes.

DESIGN

A retrospective cohort study.

SETTING

University hospital.

PATIENT(S)

A total of 6,900 patients who desired to transfer vitrified blastocysts from the same oocyte retrieval cycle as their last live birth met the inclusion criteria and were grouped according to the storage duration (1,890 patients in group 1 with storage duration < 3 years, 2,693 patients in group 2 with storage duration between 3 and 4 years, 1,344 patients in group 3 with storage duration between 4 and 5 years, 578 patients in group 4 with storage duration between 5 and 6 years and 395 patients in group 5 with storage duration ≥ 6 years but ≤ 10.5 years).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Rates of blastocyst survival, biochemical pregnancy, clinical pregnancy, miscarriage, ectopic pregnancy, and live birth and neonatal outcomes.

RESULT(S)

The survival rates of the vitrified blastocysts significantly decreased with prolonged storage from group 1 to the subsequent groups 2, 3, 4, and 5. After adjusting for potential confounding factors, the rates of biochemical pregnancy, clinical pregnancy, and live birth were significantly decreased when the vitrified blastocysts were stored for more than 6 years (group 5) compared with these for less than 3 years (group 1) but no distinct differences were found in these above-mentioned indicators among group 1, 2, 3, and group 4 (group 1 as reference). However, no significant differences were noted in the rates of miscarriage and ectopic pregnancy and neonatal outcomes on prolonged storage of vitrified blastocysts.

CONCLUSION(S)

Long-term blastocyst vitrification for more than 6 years can negatively affect the rates of biochemical pregnancy, clinical pregnancy, and live birth but does not impact neonatal outcomes.

The association between embryo storage time and treatment success in women undergoing freeze-all embryo transfer

OBJECTIVE

To investigate the relationship between the embryo frozen time and live birth rate (LBR) in women having a freeze-all cycle.

DESIGN

Retrospective cohort study.

SETTING

Academic hospital.

PATIENT(S)

Women who underwent their first vitrified-warmed cycles from January 2013 to December 2019.

INTERVENTION(S)

Embryo storage time.

MAIN OUTCOME MEASURE(S)

The primary outcome was the LBR.

RESULT(S)

A total of 14,928 women were eligible for the analysis. Women with the frozen time of transferred embryos for 2-5 months were associated with a higher LBR compared with other groups. The results were confirmed by an inverted U curve in the restricted cubic splines before as well as after adjustment for covariables, which suggested that an embryo storage time of 3-4 months was associated with the highest LBR. Subgroup analyses demonstrated that the inverted U curve relationship between embryo storage time and LBR was only observed in women with the high response. Sensitivity analyses in women with at least one good-quality embryo for transfer, in women aged <36 years at embryo transfer, or in women with double cleavage embryo transfer showed that the association remained valid. The association was weakened in women with single blastocyst transfer probably because of the small sample size in these women.

CONCLUSION(S)

An inverted U-shaped relationship was found between embryo storage time and treatment success in women with high ovarian response in freeze-all embryo transfer cycles. Prolonged storage time of >6 months was associated with reduced pregnancy rates.

Long-term cryopreservation and frozen embryo transfer do not impact clinical and neonatal outcomes: a retrospective cohort study of slow-frozen early-cleavage human embryos

This study aimed to evaluate the effect of the cryopreservation duration (up to 160 months) on the clinical and neonatal outcomes of slow-frozen early-cleavage human embryos. Clinical data collected between February 2013 and August 2017 were included in this retrospective study. Cases were classified into five groups by the duration of cryopreservation: Group 1, 6-12 months; Group 2, 13-36 months; Group 3, 37-60 months; Group 4, 61-84 months; and Group 5, >84 months. The embryo survival rate, implantation rate, clinical pregnancy rate, live-birth rate, newborn sex ratio, singleton gestational age, singleton birth weight and malformation rate were compared between the groups. The cryopreservation duration did not significantly affect the rates of clinical pregnancy (P = 0.119) and live birth (P = 0.354), the newborn sex ratio (P = 0.614) or the singleton gestational age (P = 0.212) and birthweight (P = 0.212). Although decreases in the embryo survival and implantation rates were observed in groups 4 and 5 compared with those in groups 1-3, these differences were not statistically significant (P = 0.329, P = 0.279, respectively). Long-term cryopreservation does not appear to adversely affect the clinical and neonatal outcomes of slow-frozen early-cleavage human embryos.

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

PURPOSE

Few studies explored whether prolonged cryo-storage after vitrification affects embryo competence and perinatal outcomes. This systematic review and meta-analysis aims at highlighting any putative impact of cryo-storage duration on cryo-survival, miscarriage, live birth and major malformations.

METHODS

A systematic review was performed using MEDLINE (PubMed), ISI Web of Knowledge, Scopus and Embase databases up to June 2021. Data were combined to obtain a pooled OR, and meta-analysis was conducted using a random effects model. Out of 1,389 screened abstracts, 22 papers were assessed for eligibility, and 5 studies were included (N = 18,047 embryos). Prolonged cryo-storage was defined as > 12 months (N = 3389 embryos). Subgroup analysis was performed for untested vitrified cleavage stage embryos (N = 1739 embryos) and for untested and euploid vitrified blastocysts (N = 13,596 and 2712 embryos, respectively).

RESULTS

Survival rate, miscarriage, live birth and major malformation rates were all similar in the two groups.

CONCLUSION

These data further support the safety of long-term cryo-storage of human embryos beyond 12 months. This is reassuring for good prognosis patients with surplus embryos, couples seeking a second child from supernumerary embryos and women postponing the transfer for clinical or personal reasons.

Long-Term Storage Does Not Affect the Expression Profiles of mRNA and Long Non-Coding RNA in Vitrified-Warmed Human Embryos

Although vitrification has been widely applied in assisted reproductive technology, it is unknown whether storage time has any impact on the mRNA and lncRNA expression profiles in human embryos. Eleven women (aged 23-35 years) who had undergone in vitro fertilization treatment were recruited for this study. The transcriptomes of 3 fresh eight-cell embryos and 8 surviving vitrified-warmed eight-cell embryos (4 embryos were cryostored for 3 years, and the others were cryostored for 8 years) were analyzed through single-cell RNA-Seq. No differentially expressed mRNAs or lncRNAs were identified between the 3-years group and 8-years group. A total of 128 mRNAs and 365 lncRNAs were differentially expressed in the 8 vitrified-warmed embryos compared with the fresh embryos. The vitrification-warming impact was moderate, and it was mainly related to the pathways of metabolism, stress response, apoptosis, cell cycle, cell adhesion, and signaling for TFG-β and Hippo. The analysis of target mRNAs suggested that lncRNAs might contribute to the regulation of mRNAs after vitrification-warming. Our findings indicated that long-term storage after vitrification does not affect the mRNA and lncRNA expression profiles in human embryos, however, the procedure of vitrification-warming would lead to minor alteration of transcriptome.

Effect of long-term embryo cryopreservation on subsequent frozen embryo transfer outcomes: A retrospective cohort study

Background:

The duration of cryopreservation of embryos and its effect on the subsequent pregnancy outcomes, when they have been frozen for a longer duration remains a matter of concern. There is a continuous debate among studies comparing different durations of embryo cryopreservation as the results are contradictory.

Aims:

This study aims to find out if long-term cryopreservation of embryos has any effect on pregnancy and perinatal outcomes.

Settings and Design

:Retrospective cohort study was conducted in the department of reproductive medicine and surgery in a university-level teaching hospital.

Materials and Methods:

The study included women who underwent frozen embryo transfer (FET) from autologous in vitro fertilisation between January 2012 and December 2020 with the duration of cryopreservation of more than 5 years as one group and 3–5 years as another group. Pregnancy and perinatal outcomes were analysed.

Statistical Analysis Used:

Regression analysis was performed using logistic regression by entering clinically important variables associated with pregnancy outcome, and the results were expressed as odds ratio with a 95% confidence interval (CI). All statistical analysis was performed with SPSS (version 21.0, IBM, USA).

Results:

A total of 1680 FET cycles were carried out during the study period. Among these, 75 cycles with a duration of 3–5 years and 20 cycles with a duration of more than 5 years were included. Live birth rate (LBR) was 40.8% in the 3–5 years group and 35% in the more than 5 years group. After adjusting for important confounders, the LBR has no significant association in the more than 5 years group (adjusted odds ratio 1.07; 95% CI 0.34–3.32; P = 0.913) compared to the 3–5 years group.

Conclusion:

The duration of cryopreservation of embryos has no statistically significant effect on the pregnancy and perinatal outcomes.

Clinical, obstetric and perinatal outcomes after vitrified-warmed euploid blastocyst transfer are independent of cryo-storage duration

RESEARCH QUESTION

The study aimed to retrospectively evaluate the impact of cryo-storage duration on clinical, obstetric and perinatal outcomes after vitrified-warmed euploid blastocyst transfer.

DESIGN

This was an observational study including 2688 vitrified-warmed euploid single blastocyst transfers that was conducted at a private IVF centre between May 2013 and March 2020. It included a total of 1884 women (age 38 ± 3 years) undergoing at least one transfer after preimplantation genetic testing for aneuploidies. The euploid blastocysts transferred were clustered into seven groups according to the cryo-storage duration between vitrification and warming: ≤60 days (n = 646; control group), 61-90 days (n = 599), 91-180 days (n = 679), 181-360 days (n = 405), 361-720 days (n = 144), 721-1080 days (n = 118) and >1080 days (n = 97). The primary outcome was the live birth rate (LBR) per transfer. The secondary outcomes were miscarriage rate, obstetric and perinatal issues. The data were adjusted for confounders through logistic or linear regressions.

RESULTS

A significantly lower LBR was reported for transfers performed within 91-180 days (n = 291/679, 42.9%; P = 0.017), 181-360 days (n = 169/405, 41.7%; P = 0.016) and 361-720 days (n = 57/144, 39.6%; P = 0.034) versus ≤60 days (n = 319/646, 49.4%). However, this was mainly due to top-quality embryos being transferred first when more euploid blastocysts were available, thereby leaving lower quality ones for subsequent procedures. Indeed, the multivariate odds ratios adjusted for confounders showed similar results across all cryo-storage duration clusters. No difference was reported also for all secondary outcomes.

CONCLUSIONS

Cryo-storage duration even beyond 3 years from blastocyst vitrification does not affect clinical, obstetric and perinatal outcomes.

Storage, transport, and disposition of gametes and embryos: legal issues and practical considerations

Cryopreservation of reproductive material has dramatically improved clinical outcomes for patients all over the world. At the same time the practice has produced significant legal, ethical, and practical challenges to physicians and practices who use this technique. Failing to meet the expectations of patients, for example by losing material because of a freezer failure, has significant implications for the reproductive facility. Similarly, improperly transporting or receiving gametes or embryos can result in substantial risk to a practice. Perhaps the most widely publicized conundrum is how best to manage embryos that are abandoned. This paper will describe the legal principles and best practices that should be incorporated into the management of a fertility cryopreservation program.

Effect of embryo cryopreservation duration on pregnancy-related complications and birthweight after frozen-thawed embryo transfer: a retrospective cohort study

Frozen embryo transfer (FET) has been adopted by growing number of reproductive medicine centers due to the improved outcome compared with fresh embryo transfer. However, few studies have focused on the impact of embryo cryopreservation duration on pregnancy-related complications and neonatal birthweight. Thus, a retrospective cohort study including all FET cycles with livebirth deliveries in a university affiliated hospital from May 2010 to September 2017 was conducted. These deliveries were grouped by the cryopreservation duration of the transferred embryo (≤3 months, 4-6 months, 7-12 months, and >12 months). The associations between embryo cryopreservation duration and pregnancy-related complications were evaluated among the groups using multinomial logistic regression. Neonatal birthweight was compared according to the stratification of singletons and multiples using multinomial and multilevel logistic regression, respectively. Among all 12,158 FET cycles, a total of 3864 livebirth deliveries comprising 2995 singletons and 1739 multiples were included. Compared with those within 3 months, women undergoing FET after a cryopreservation time longer than 3 months did not show any increased risk of gestational diabetes mellitus, gestational hypertension, preeclampsia, meconium staining of the amniotic fluid, or preterm birth. Furthermore, the risk of lower birthweight, macrosomia, small-for-gestational-age, or large-for-gestational-age for either singletons or multiples was not affected by long-term cryopreservation. In summary, embryo cryopreservation duration does not have negative effects on pregnancy-related complications or birthweight after FET.

The effect of storage time after vitrification on pregnancy and neonatal outcomes among 24 698 patients following the first embryo transfer cycles

STUDY QUESTION

To evaluate the impact of storage time after vitrification on embryo viability, pregnancy outcomes and neonatal outcomes.

SUMMARY ANSWER

The prolonged storage time of vitrified embryos negatively affected pregnancy outcomes, including biochemical pregnancy rate, clinical pregnancy and live birth rate; but did not influence neonatal outcomes.

WHAT IS KNOWN ALREADY

Although vitrification has been the fundamental tool of ART treatments in recent years, few studies have explored the influence of storage period after vitrification on embryonic and clinical outcomes.

STUDY DESIGN, SIZE, DURATION

A retrospective study was performed among 24 698 patients with the first vitrified embryo transfer following a freeze-all strategy during the period from January 2011 to December 2017.

PARTICIPANTS/MATERIAL, SETTING, METHODS

A total of 24 698 patients met the inclusion criteria and were grouped according to the storage time (11 330 patients in Group 1 with storage time <3 months, 9614 patients in Group 2 with storage time between 3 and 6 months, 3188 patients in Group 3 with storage time between 6 and 12 months and 566 in Group 4 with storage time between 12 and 24 months). The pregnancy outcomes and neonatal outcomes were compared between different storage time groups. Multivariate logistic regression and linear regression were performed to evaluate the independent effect of storage time on clinical outcomes, adjusting for important confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

After adjustment for potential confounding factors, the chance of biochemical pregnancy (Group 1 as reference; Group 2: adjusted odds ratio (aOR) = 0.92, 95% CI 0.87-0.97; Group 3: aOR = 0.83, 95% CI 0.76-0.90; Group 4: aOR = 0.68, 95% CI 0.56-0.81), clinical pregnancy (Group 2: aOR = 0.91, 95% CI 0.86-0.96; Group 3: aOR = 0.80, 95% CI 0.73-0.87; Group 4: aOR = 0.65, 95% CI 0.54-0.79) and live birth (Group 2: aOR = 0.89, 95% CI 0.85-0.95; Group 3: aOR = 0.83, 95% CI 0.76-0.91; Group 4: aOR = 0.59, 95% CI 0.48-0.72) significantly decreased with the increasing storage time, whereas the relationship between miscarriage, ectopic pregnancy and storage time did not reach statistical significance. In addition, there was no evidence of differences in adverse neonatal outcomes (preterm birth, low birthweight, high birthweight, macrosomia or birth defects) between groups.

LIMITATION, REASONS FOR CAUTION

Our study was limited by the retrospective design from a single center, the conclusion from our study needs to be verified in further studies.

WIDER IMPLICATIONS OF THE FINDINGS

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.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (grant nos. 81903324, 81771533, 81571397, 81701523), National Key Research and Development Program of China (grant no. SQ2018YFC100163). None of the authors have any conflicts of interest to declare.

Storage Time of Cryopreserved Embryos and Pregnancy Outcomes: A Dose-Response Meta-Analysis

Purpose Cryopreservation techniques have become an essential part of assisted reproduction technology. Embryos may be cryopreserved for several years before transfer, and the safety of long-term cryopreservation needs to be considered. This dose-response meta-analysis was conducted to evaluate whether there were dose-response relationships between the storage time of cryopreserved embryos and pregnancy outcomes such as survival rate, implantation rate, miscarriage rate, clinical pregnancy rate, and congenital malformation rate. Methods After searching the databases PubMed, Embase, MEDLINE, CCRT and related reviews up until June 4, 2020, seven studies were included for analysis. Two reviewers extracted the relevant information and independently assessed the study quality using the Newcastle-Ottawa scale. Potential linear or non-linear dose-response relationships were assessed with a random-effect dose-response meta-analysis. Results No dose-response association was found between duration of embryo cryostorage and survival rate, implantation rate, miscarriage rate, clinical pregnancy rate or congenital malformation rate. Conclusion The interval between the start of embryo cryopreservation and frozen/thawed embryo transfer does not influence pregnancy outcomes.

The Impact of Embryo Storage Time on Pregnancy and Perinatal Outcomes and the Time Limit of Vitrification: A Retrospective Cohort Study

BACKGROUND

The technique of embryo cryopreservation has been increasingly applied in clinical settings. However, there has been a concern about the safety and efficacy of long-term freezing of embryos. Therefore, the aim of this study was to evaluate whether storage time of vitrification had any effects on pregnancy as well as perinatal outcomes, further, to explore the appropriate time limit of vitrification.

METHODS

The study included women who underwent at least one frozen-thawed cycle with single embryo transfer between January 1^st, 2016 and September 30^th, 2019. Patients were assigned into 3 groups according to the storage time (<3 months, 3-12 months and >12 months) to evaluate the impact of embryo storage time on pregnancy and perinatal outcomes. To further investigate the time limit of vitrification, propensity score matching was used to compare the primary outcomes of patients with storage time of 1-3 years, 3-5 years, and >5 years to those stored for ≤1 year.

RESULTS

A total of 9806 frozen-thawed embryo transfer cycles were included in our study. After adjustment for confounding variables, no significant differences were found in pregnancy outcomes among groups. However, postponement of transfer increased the risks of large for gestational age and placenta previa. In addition, after propensity score matching, 171 cycles with storage time >5 years were matched with those ≤1 year, both the clinical pregnancy rate and live birth rate decreased significantly when the storage time exceeded 5 years.

CONCLUSIONS

The duration of vitrification did not significantly affect the pregnancy outcomes within 5 years period. However, the clinical pregnancy rate and live birth rate both decreased significantly when the duration of vitrification exceeded 5 years. It is worth noting that the conclusion was drawn from a small sample study after propensity score matching and should be treated with caution. In addition, the cycles were from different time periods, which could have an impact on the results.

Prolonged Cryopreservation Negatively Affects Embryo Transfer Outcomes Following the Elective Freeze-All Strategy: A Multicenter Retrospective Study

BACKGROUND

With the development of embryo freezing and warming technology, frozen-thawed embryo transfer (FET) has been widely utilized. However, studies investigating the association between cryopreservation duration and FET outcomes are limited and controversial, and previous studies did not conduct stratification analyses based on demographic or clinical characteristics.

METHODS

This multicenter retrospective study included 17,826 women who underwent their first FET following the freeze-all strategy during the period from January 2014 to December 2018. Duration of cryopreservation was categorized into five groups: 3-8 weeks, 8-12 weeks, 12-26 weeks, 26-52 weeks, and >52 weeks. Modified Poisson regression and multivariate logistic regression were used to assess the association between cryostorage time of vitrified embryos and transfer outcomes. Moreover, further stratification analyses were performed according to variables with p <0.05 in multivariate models.

RESULTS

In this large multicenter study, we observed that storage duration was inversely associated with the possibility of pregnancy and live birth (p <0.001), but not with the risk of ectopic pregnancy and miscarriage. Stratification analyses based on maternal age, the number of oocytes retrieved, and condition of embryo transferred indicated that the inverse correlation was significant in the subpopulation with characteristics: (1) less than 40 years old, (2) more than 3 oocytes retrieved, and (3) only high-quality blastocysts transferred.

CONCLUSION

The results of this large, multicenter, retrospective study suggested that prolonged cryopreservation was inversely associated with the probability of pregnancy and live birth. Therefore, for patients who adopt a freeze-all strategy, early FET might achieve a better outcome.

Does duration of cryostorage affect survival rate, pregnancy, and neonatal outcomes? Large-scale single-center study of slush nitrogen (SN2 ) vitrified-warmed blastocysts

OBJECTIVE

To evaluate the effects of the duration of cryostorage on clinical outcomes after embryo transfer of vitrified blastocysts stored in an open-device slush-nitrogen (SN₂ ) system.

METHODS

A retrospective cohort study was carried out on 1632 autologous vitrified-warmed blastocyst transfer cycles between January 2013 and June 2014. Duration of cryostorage was divided into four groups: Group I: 0-6 months (n=937); Group II: 7-12 months (n=299); Group III: 13-24 months (n=165); and Group IV: ≥25 months (n=231). The effects of the duration of cryostorage on the survival rate (SR), clinical pregnancy rate (CPR), live birth rate (LBR), and neonatal outcomes of vitrified blastocysts stored in an open-device SN₂ system were evaluated.

RESULTS

There were no significant differences between groups in SR, CPR, LBR, and neonatal outcomes after autologous vitrified-warmed blastocyst transfer. Multivariate logistic regression analysis showed no effect on LBR from duration of cryostorage.

CONCLUSION

Vitrification using SN₂ and long-term cryostorage in an open-device system are safe and effective and do not significantly affect clinical outcomes after embryo transfer.

Vitrification of the human embryo: a more efficient and safer in vitro fertilization treatment

Cryopreservation has become a central pillar in assisted reproduction, reflected in the exponential increase of "freeze all" cycles in the past few years. Vitrification makes it possible to cool and warm human eggs and embryos with far less cryo-damage than 'slow-freeze' and allows nearly intact survival of embryos with very high survival rates for eggs as well. This has resulted in a complete transformation how we manage treatment for in vitro fertilization patients. Fresh transfers can be avoided without compromising outcomes, and in fact, cumulative pregnancy/delivery rates may be improved by performing sequential elective "frozen" single embryo transfers. Some recent evidence suggests that previously vitrified embryos give better perinatal outcomes than fresh embryo transfers. Frozen embryo transfer, especially when coupled with preimplantation genetic testing allows for highly efficient single embryo transfers that translate to more singleton and therefore safer pregnancies, as well as healthier babies. Additionally, vitrification has also opened new options for patients, most notably fertility preservation (through oocyte cryopreservation), and donor egg banking.

Early detection of cryostorage tank failure using a weight-based monitoring system

PURPOSE

To study the relationship between liquid nitrogen loss and temperature in cryostorage dewars and develop an early-warning alarm for impending tank failure.

METHODS

Cryostorage dewars were placed on custom-engineered scales, and weight and temperature data were continuously monitored in the setting of slow, medium, and fast rate-loss of LN₂ to simulate three scenarios of tank failure.

RESULTS

LN₂ Tank weights and temperatures were continuously monitored and recorded, with a calculated alarm trigger set at 10% weight loss and temperature of - 185 °C. With an intact tank, a 10% loss in LN₂ occurred in 4.2-4.9 days. Warming to - 185 °C occurred in 37.8-43.7 days, over 30 days after the weight-based alarm was triggered. Full evaporation of LN₂ required ~ 36.8 days. For the medium rate-loss simulation, a 10% loss in LN₂ occurred in 0.8 h. Warming to - 185 °C occurred in 3.7-4.8 h, approximately 3 h after the weight-based alarm was triggered. For the fast rate-loss simulation, a 10% weight loss occurred within 15 s, and tanks were depleted in under 3 min. Tank temperatures began to rise immediately and at a relatively constant rate of 43.9 °C/h and 51.6 °C/h. Temperature alarms would have sounded within 0.37 and 0.06 h after the breech.

CONCLUSIONS

This study demonstrates that a weight-based alarm system can detect tank failures prior to a temperature-based system. Weight-based monitoring could serve as a redundant safety mechanism for added protection of cryopreserved reproductive tissues.