The effect of repeated cryopreservation and thawing using cryotip on the clinical outcomes of embryos

Does double cryopreservation as well as double biopsy affect embryo viability and clinical outcomes? Evidence from a systematic review of the literature

This study evaluates the effects of double cryopreservation and re-biopsy on embryo viability and clinical outcomes. Studies of interest were selected from an initial cohort of 1027 potentially relevant records retrieved. PubMed was systematically searched for peer-reviewed original papers identified by keywords and medical subject heading terms. Moreover, we elaborated the evidence tables for double cryopreservation and re-biopsy separately. Data were systematically extracted, focusing on live birth, survival, clinical pregnancy, and miscarriage rates. For each study, we identified absolute numbers (numerator and denominator) related to clinical outcomes. Finally, for each outcome, we calculated the percentage change between the control and study groups. Among studies on double cryopreservation, 13 out of 22 reported no effect on clinical outcomes, suggesting contradictory results. Similarly, findings on re-biopsy were controversial, with seven out of 12 studies showing negative effects on survival and clinical outcomes, while five reported no impact. In our analysis of the evidence tables, we observed a reduction in live birth rates of 22.2% and 39.3% in blastocysts undergoing double vitrification and re-biopsy, respectively. These findings suggest that repeated micromanipulations can impair embryo competence. Therefore, double cryopreservation and re-biopsy should be limited in the selected cases without other options by consulting patients about the possible harmful effects.

Embryonic and neonatal outcomes following double vitrification/thawing: a systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis aimed to evaluate the impact of double vitrification/thawing (DVT) versus single vitrification/thawing (SVT) on key embryonic and neonatal outcomes.

DATA EXTRACTION

Information sources included systematic search in PubMed, Scopus, and Cochrane databases up to September 7, 2024. Data from each qualifying study were extracted by two reviewers using a standardized electronic data gathering form.

DATA ANALYSIS

Mantel-Haenszel odds ratio (MHOR) and mean difference (MD) with 95% confidence intervals (CI) were calculated using both fixed and random-effects models. Subgroup analyses were based on biopsy status, number of biopsy rounds, extended culture between rounds of vitrification, and embryo transfer strategy.

RESULTS

A total of 35 studies involving 46,749 embryo transfer cycles were included. After excluding studies that used slow freezing, 28 studies were included in the meta-analyses. The findings indicated that DVT is associated with significant reductions in cryosurvival rates (MHOR: 0.4; CI: 0.3 to 0.8; P < 0.01), biochemical pregnancy (MHOR: 0.7; CI: 0.6 to 0.8; P < 0.01), clinical pregnancy (MHOR: 0.7; CI: 0.5 to 0.8; P < 0.01), and live birth rates (MHOR: 0.6; CI: 0.5 to 0.7; P < 0.01). Additionally, there was a significant increase in the miscarriage rate (MHOR: 1.4; CI: 1.2 to 1.7; P < 0.01). No significant differences were found in neonatal outcomes.

CONCLUSION

Poor-quality evidence suggests that the transfer of double-vitrified embryos might be associated with significantly lower rates of cryosurvival, pregnancy, and live births; however, it does not appear to affect neonatal outcomes such as birth weight and gestational age at birth. Given the small sample size in some subgroups, the high risk of selection, confounding and missing data biases, and the high level of heterogeneity for some outcomes, these findings should be interpreted cautiously.

Systematic review and meta-analysis of the impact of the refreezing and rebiopsy embryos on reproductive outcomes in patients undergoing freeze-thaw embryo transfer

IMPORTANCE

During frozen-thawed embryo transfer (FET) cycles in in vitro fertilization/intracytoplasmic sperm injection patients (including preimplantation genetic testing patients), transfer of embryos that have been thawed may be abandoned for medical or personal reasons, resulting in the need to refreeze embryos. Typically, embryos from patients undergoing preimplantation genetic testing are cryopreserved after biopsy, pending test results. However, in the absence of a clear result, another biopsy is required, and the embryo is frozen again to await the results for future use.

OBJECTIVE

To explore whether refreezing and rebiopsy affect reproductive outcomes.

DATA SOURCES

Computer search was conducted in PubMed, Embase, Cochrane Library, Web of Science, CBM, CNKI, WanFang Data, and VIP databases and searched until May 2023.

STUDY SELECTION AND SYNTHESIS

STATA/MP software was used for conducting data analysis. Dichotomous outcome data were pooled to calculate odds ratios (ORs) and their corresponding 95% confidence intervals (CIs). Continuous outcome data were combined using an inverse variance model to determine the mean difference between the two groups. Random-effects and fixed-effects meta-analysis models were employed to assess heterogeneity. Subgroup analysis was conducted on the basis of different freezing methods and various embryo types.

MAIN OUTCOMES

The primary outcome measure was the live birth rate (LBR), with secondary indicators including clinical pregnancy rate (CPR), implantation rate, miscarriage rate (MR), ectopic pregnancy, preterm delivery, mean birth weight of neonates, and neonatal malformation.

RESULTS

This study included 19 retrospective studies with a total of 11,024 FET cycles. Across the FET cycles, recryopreservation, compared with once-cryopreservation, demonstrated reduced LBRs (OR, 0.79; 95% CI, 0.60 -0.92; I2 = 21.7%), reduced CPRs (OR, 0.74; 95% CI, 0.60 -0.92; I2 = 56.9%), and increased MRs (OR, 1.27; 95% CI, 1.03 -1.55; I2 = 37.1%). Pregnancy outcomes after rebiopsies, revealing significantly lower LBRs after rebiopsies than after single biopsy (OR, 0.65; 95% CI, 0.45 -0.94; I2 = 43.5%). Similarly, rebiopsies were associated with reduced CPRs (OR, 0.75; 95% CI, 0.54 -1.03; I2 = 29.6%) and increased MRs (OR, 1.54; 95% CI, 0.89 -2.66; I2 = 13.0%) compared with single biopsy.

CONCLUSION AND RELEVANCE

Refrozen embryos compared with once-frozen embryos suggest a decrease in the LBRs and CPRs, coupled with an increase in the MRs, with negligible influence on neonatal outcomes. Similarly, rebiopsy yields comparable results, leading to a reduction in the LBRs.

Effects of first and second division modes on euploidy acquisition in human embryo

The aim of this study was to non-invasively investigate euploid embryos using methods other than pre-implantation genetic testing for aneuploidy. The study focused on direct cleavage (DC) observed during early embryo development. We also investigated the relationship between the mode of early embryo division and embryo ploidy. Embryos were divided into the normal cleavage (NC) and DC groups, and the DC group was further subdivided into the DC-First (DC-F) and DC-Second (DC-S) groups, depending on whether DC was observed at the first or second cleavage, respectively. The acquisition rates of euploid embryos and embryos appropriate for transfer were compared between the groups. Our results revealed that the timing of the first division did not differ between blastocyst grades or in embryos with varying degrees of ploidy. Further, the timing of the first cleavage did not affect the acquisition rate of embryos appropriate for transfer and euploid embryo formation rate did not significantly differ between the DC and NC groups. We also noted that for embryos appropriate for transfer, euploidy acquisition rate did not differ significantly between the DC and NC groups. Further, the euploidy acquisition rate of embryos did not differ between the DC-F and DC-S groups. However, the acquisition rate of embryos appropriate for transfer, including those with low mosaicism, was significantly higher in the DC-S group than in the DC-F group. These findings indicated that the number of good-quality blastocysts formed was significantly higher in the NC group than in the DC group and the acquisition rate of embryos appropriate for transfer, including those with low mosaicism, was significantly higher in the DC-S group than in the DC-F group.

Formation of the first plane of division relative to the pronuclear axis predicts embryonic ploidy

RESEARCH QUESTION

Is there a relationship between the pronuclear axis and the first cleavage plane formation in human pronuclear-stage embryos, and what are the effects on ploidy and clinical pregnancy rates?

DESIGN

Transferred embryos were followed up until their prognoses. A total of 762 embryos formed two cells and reached the blastocyst stage after normal fertilization in a time-lapse incubator. Embryos were classified into three groups: group A: embryos in which the first plane of division was formed parallel to the axis of the pronucleus; group B: embryos in which cases of oblique formation were observed; and group C: embryos in which cases of perpendicular formation were observed.

RESULTS

The euploidy rate was significantly higher in groups A and B than those in group C (P < 0.01), whereas the aneuploidy rate was significantly higher in group C (P < 0.01) than in groups A and B. No differences were found between the three groups in frequency of positive HCG-based pregnancy tests, frequency of clinical pregnancies, miscarriage rates or delivery rates.

CONCLUSIONS

The formation pattern of the first plane of division relative to the pronuclear axis was a predictor of embryonic ploidy, with a reduced rate of euploidy and a high probability of aneuploidy observed when the first plane of division was perpendicular to the pronuclear axis.

Recryopreservation impairs blastocyst implantation potential via activated endoplasmic reticulum stress pathway and induced apoptosis

Recryopreservation (recryo) is occasionally applied in clinical, while the underlying mechanism of impaired clinical outcomes after recryo remains unclear. In this study, frozen embryo transfer (FET) cycles of single blastocyst transfer in an academic reproductive medicine center were enrolled. According to the number of times blastocysts experienced cryopreservation, they were divided into the cryopreservation (Cryo) group and the Recryo group. Donated human blastocysts were collected and detected for mechanism exploration. It was found that recryo procedure resulted in impaired blastocyst developmental potential, including decreased implantation rate, reduced biochemical pregnancy rate, declined clinical pregnancy rate, higher early miscarriage rate, and lower live birth rate. Moreover, recryo led to impaired trophectoderm (TE) function, exhibiting lower human chorionic gonadotropin levels 12 days after FET. In addition, single-cell RNA sequencing showed that the expression of genes involved in cell adhesion and embryo development were altered. More specifically, activated endoplasmic reticulum (ER) pathway and induced apoptosis were further verified by immunofluorescence and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay involving in the recryo procedure. In conclusion, recryo could interfere with the process of blastocyst implantation by impairing TE function, affecting blastocyst adhesion, activating ER stress pathway and inducing apoptosis. It provides caution to embryologists about the potential risk of recryopreservation.

Effect of freeze-thawing, cell collection, and laser irradiation cycles on mosaicism occurrence in preimplantation genetic testing for aneuploidy

OBJECTIVE

In preimplantation genetic testing for aneuploidy, opinions regarding the handling of mosaic embryos vary. In this study, we aimed to investigate the effects of freeze-thawing, the number of cells obtained, and the number of laser irradiation cycles on the degree of embryonic mosaicism.

STUDY DESIGN

This study was conducted in three parts. First, we classified specimens into the normal biopsy (control) (119 patients, 304 blastocysts) and thawed-biopsy (TB group) (26 patients, 72 blastocysts)) groups. The control and TB groups were then classified into three categories (euploidy, mosaic and aneuploidy) according to next-generation sequencing (NGS) results, and the number of cells collected and laser irradiation cycles were compared for each category. Subsequently, the effects of differences in the number of cells collected and laser irradiation cycles on NGS results were investigated in the control and TB groups. Finally, data on cell collection and laser irradiation cycles and NGS analysis results for the groups were compared.

RESULTS

The TB group had a significantly higher incidence of chromosomal mosaicism than the control group. Neither the number of cells collected nor the laser irradiation cycles affected the percentage of chromosomal mosaicism. However, the freeze-thaw process increased the occurrence of mosaicism.

CONCLUSIONS

This study showed that repeated freeze-thaw cycles increase the incidence of mosaicism, but the embryos are not aneuploid and are therefore suitable for transfer.

Effect of repeated vitrification of human embryos on pregnancy and neonatal outcomes

BACKGROUND

Repeated cryopreservation of embryos should occasionally be considered when embryos were not suitable for transfer. The effect of re-cryopreservation on embryos remains contentious.

METHODS

This retrospective cohort study aimed to evaluate the pregnancy and neonatal outcomes of twice vitrificated blastocyst derived from once vitrified embryos. Total 410 vitrified-warmed blastocyst transfer cycles were divided into two groups according to the times of embryo vitrification: (1) vitrified blastocysts derived from fresh blastocysts (control group, n = 337); (2) twice vitrified blastocysts derived from once vitrified embryos (n = 73). The primary outcome was live birth rate. Multivariable logistic or linear regression analysis model was performed to describe the association between embryo cryopreservation times and clinical outcomes.

RESULTS

No difference was observed in female age at retrieval and transfer, infertility period, body mass index (BMI), infertility type, endometrial thickness, and embryo transfer numbers between the two groups. The pregnancy outcomes of embryos in repeated cryopreservation group were comparable to those of embryos in control group, including implantation rate, clinical pregnancy rate, and live birth rate. In multivariate logistic regression analysis, the cryopreservation times did not affect the outcomes of biochemical pregnancy, clinical pregnancy, and live birth. Moreover, there was no difference in gestational age, birthweight and sex ratio of singleton newborns between groups. After correcting several possible confounding variables, no significant association was observed between cryopreservation times and neonatal birthweight.

CONCLUSION

In conclusion, pregnancy and neonatal outcomes achieved with twice vitrified blastocyst transfer were comparable to those achieved with vitrified blastocyst transfer in control group.

Smooth endoplasmic reticulum cluster presence does not affect embryo ploidy

PURPOSE

We examined the impacts of the smooth endoplasmic reticulum cluster (sERC) presence on embryonic development and blastocyst ploidy.

METHODS

Patients who underwent oocyte retrieval from January 2019 to November 2021 were included in the study. We classified the oocytes into three groups: normal oocytes in the sERC ( -) cycle, normal oocytes in the sERC ( +) cycle, and sERC ( +) oocytes. Next, the levels of serum estradiol, progesterone, anti-Mullerian hormone, follicle-stimulating hormone, and human menopausal gonadotropin were compared between the groups. Moreover, fertilization, degeneration, and abnormal fertilization rates were compared between groups. To investigate developmental outcomes, the blastocyst and good-quality blastocyst rates after intracytoplasmic sperm injection were compared. The quality of the transferred blastocysts was evaluated at follow-up. Additionally, embryos were submitted for next-generation sequencing analysis to examine the effect of sERC presence on ploidy.

RESULTS

The sERC ( +) group had significantly higher serum estradiol, serum progesterone, and serum anti-Mullerian hormone concentrations compared to those in the sERC ( -) group (P < 0.01). The abnormal fertilization rate was higher in the sERC ( +) cycle-sERC ( +) oocyte group (16.1%; 37/230) than in the sERC ( +) cycle-normal oocyte (6.2%; 63/971) and sERC ( -) cycle-normal oocyte groups (7.1%; 174/2467) (P < 0.01). After embryo transfer, nine women gave birth, and no confirmed congenital anomalies were observed. There was no significant difference in ploidy between the sERC ( +) and sERC ( -) groups.

CONCLUSION

The occurrence rates of embryos with euploidy were similar between the sERC ( +) and sERC ( -) groups.

The effects of differences in trophectoderm biopsy techniques and the number of cells collected for biopsy on next‐generation sequencing results

Purpose

To examine how differences in trophectoderm biopsy techniques affect the frequency of mosaic embryos and sequencing results.

Methods

We examined differences in next‐generation sequencing (NGS) analysis results among operators or according to biopsy technique. Additionally, we determined the cut‐off for the number of collected cells to predict the occurrence of mosaicism. We collected cells according to the cut‐off value and examined whether there was a difference in the NGS analysis results between the pulling and flicking methods.

Results

There was no difference in the NGS analysis results among the operators. Regarding re‐biopsy, changes in the mosaic were observed in all specimens. The cut‐off value for the number of collected cells was five, and when more than five cells were collected, there was no difference in the NGS analysis results between the two methods.

Conclusions

We demonstrated that if trophectoderm biopsy techniques and NGS are stable, the cell collection location has a greater effect on NGS results than the biopsy technique.

A novel trophectoderm biopsy technique for all blastocyst stages

Purpose

This study was conducted to assess the effectiveness of a new trophectoderm (TE) biopsy method that does not require prior opening of the zona pellucida at the blastocyst stage.

Methods

TE biopsy was conducted using a modified extrusion method for embryos during the cleavage stage. In this method, culture medium was injected into the perivitelline space to help extrude TE cells from the zona pellucida before TE biopsy.

Results

Our extrusion method preserves the embryo culture environment until immediately before biopsy because it does not require opening of the zona pellucida prior to TE biopsy. Furthermore, this method does not require a waiting time for blastocyst hatching after laser irradiation, thereby minimizing damage to the embryos and maintaining the time schedule of culture operations.

Conclusions

TE biopsy using this novel extrusion method may be useful in various applications, including the collection of TE cells for next-generation sequencing analysis.