Vitrification of human mature oocytes in clinical practice

Minimum number of mature oocytes needed to obtain at least one euploid blastocyst according to female age in in vitro fertilization treatment cycles

OBJECTIVE

To find a useful tool for estimating the minimum number of metaphase II (MII) oocytes needed to obtain at least one euploid blastocyst according to female age.

DESIGN

Retrospective analysis of in vitro fertilization (IVF) treatment cycles with preimplantational genetic testing for aneuploidies (PGT-A) performed over 5 years in IVIRMA Valencia (Spain), January 2017-March 2022. Approval from the Institutional Review Board of IVI Valencia (2204-VLC-040-CR).

SETTING

Private infertility clinic in Spain.

PATIENTS

Eligible patients were undergoing their first IVF-PGT-A treatment cycle, in which at least one MII oocyte was obtained, regardless of oocyte and semen origin. Oocyte donation cycles were included in the donor group (≤34 years old). Treatment cycles from women with their own oocytes were selected only when the oocytes were aged ≥35 years (patient group). Only trophoectoderm biopsies performed on days 5 or 6 of development and analyzed using next-generation sequencing were included. Preimplantational genetic testing for aneuploidy cycles because of a known abnormal karyotype were excluded.

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

Number of MII oocytes needed to obtain one euploid blastocyst according to female age.

RESULTS

A total of 2,660 IVF-PGT-A treatment cycles were performed in the study period in the eligible population (patients group = 2,462; donors group =198). The mean number of MII oocytes needed to obtain one euploid blastocyst increased with age, as did the number of treatment cycles that did not get at least one euploid blastocyst. An adjusted multivariate binary regression model was designed using 80% of the patient group sample (n = 2,462; training set). A calculator for the probability of obtaining at least one euploid blastocyst was created using this model. The validation of this model in the remaining 20% of the patient group sample (n = 493; validation set) showed that it could estimate the event of having at least one euploid blastocyst with an accuracy of 72.0%.

CONCLUSIONS

Our results show a preliminary model capable of predicting the number of MII oocytes needed to obtain at least one euploid blastocyst according to female age, calculated with the largest database of IVF-PGT-A treatment cycles ever used for this purpose, including only treatment cycles using next-generation sequencing on trophoectoderm biopsies. Once this model has been properly validated, it could help with decision-making for both clinicians and patients coming to an infertility clinic.

Trophectoderm cells of human mosaic embryos display increased apoptotic levels and impaired differentiation capacity: a molecular clue regarding their reproductive fate?

STUDY QUESTION

Are there cell lineage-related differences in the apoptotic rates and differentiation capacity of human blastocysts diagnosed as euploid, mosaic, and aneuploid after preimplantation genetic testing for aneuploidy (PGT-A) based on concurrent copy number and genotyping analysis?

SUMMARY ANSWER

Trophectoderm (TE) cells of mosaic and aneuploid blastocysts exhibit significantly higher levels of apoptosis and significantly reduced differentiation capacity compared to those of euploid blastocysts.

WHAT IS KNOWN ALREADY

Embryos diagnosed as mosaic after PGT-A can develop into healthy infants, yet understanding the reasons behind their reproductive potential requires further research. One hypothesis suggests that mosaicism can be normalized through selective apoptosis and reduced proliferation of aneuploid cells, but direct evidence of these mechanisms in human embryos is lacking. Additionally, data interpretation from studies involving mosaic embryos has been hampered by retrospective analysis methods and the high incidence of false-positive mosaic diagnoses stemming from the use of poorly specific PGT-A platforms.

STUDY DESIGN, SIZE, DURATION

Prospective cohort study performing colocalization of cell-lineage and apoptotic markers by immunofluorescence (IF). We included a total of 64 human blastocysts donated to research on Day 5 or 6 post-fertilization (dpf) by 43 couples who underwent in vitro fertilization treatment with PGT-A at IVI-RMA Valencia between September 2019 and October 2022. A total of 27 mosaic blastocysts were analyzed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study consisted of two phases: Phase I (caspase-3, n = 53 blastocysts): n = 13 euploid, n = 22 mosaic, n = 18 aneuploid. Phase II (terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), n = 11 blastocysts): n = 2 euploid, n = 5 mosaic, n = 4 aneuploid. Following donation for research, vitrified blastocysts were warmed, cultured until re-expansion, fixed, processed for IF, and imaged using confocal microscopy. For each blastocyst, the following cell counts were conducted: total cells (DAPI+), TE cells (GATA3+), inner cell mass (ICM) cells (GATA3-/NANOG+), and apoptotic cells (caspase-3+ or TUNEL+). The incidence of apoptosis was calculated for each blastocyst by dividing the number of caspase-3+ cells (Phase I) or TUNEL+ cells (Phase II) by the number of TE or ICM cells. Statistical analysis was performed according to data type and distribution (P < 0.05 was considered statistically significant).

MAIN RESULTS AND THE ROLE OF CHANCE

Phase I: Mosaic blastocysts displayed a similar number of total cells (49.6 ± 15 cells at 5 dpf; 58.8 ± 16.9 cells at 6 dpf), TE cells (38.8 ± 13.7 cells at 5 dpf; 49.2 ± 16.2 cells at 6 dpf), and ICM cells (10.9 ± 4.2 cells at 5 dpf; 9.7 ± 7.1 cells at 6 dpf) compared to euploid and aneuploid blastocysts (P > 0.05). The proportion of TE cells retaining NANOG expression increased gradually from euploid blastocysts (9.7% = 63/651 cells at 5 dpf; 0% = 0/157 cells at 6 dpf) to mosaic blastocysts (13.1% = 104/794 cells at 5 dpf; 3.4% = 12/353 cells at 6 dpf) and aneuploid blastocysts (27.9% = 149/534 cells at 5 dpf; 4.6% = 19/417 cells at 6 dpf) (P < 0.05). At the TE level, caspase-3+ cells were frequently observed (39% = 901/2310 cells). The proportion of caspase-3+ TE cells was significantly higher in mosaic blastocysts (44.1% ± 19.6 at 5 dpf; 43% ± 16.8 at 6 dpf) and aneuploid blastocysts (45.9% ± 16.1 at 5 dpf; 49% ± 15.1 at 6 dpf) compared to euploid blastocysts (26.6% ± 16.6 at 5 dpf; 17.5% ± 14.8 at 6 dpf) (P < 0.05). In contrast, at the ICM level, caspase-3+ cells were rarely observed (1.9% = 11/596 cells), and only detected in mosaic blastocysts (2.6% = 6/232 cells) and aneuploid blastocysts (2.5% = 5/197 cells) (P > 0.05). Phase II: Consistently, TUNEL+ cells were only observed in TE cells (32.4% = 124/383 cells). An increasing trend was identified toward a higher proportion of TUNEL+ cells in the TE of mosaic blastocysts (37.2% ± 21.9) and aneuploid blastocysts (39% ± 41.7), compared to euploid blastocysts (23% ± 32.5), although these differences did not reach statistical significance (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION

The observed effects on apoptosis and differentiation may not be exclusive to aneuploid cells. Additionally, variations in aneuploidies and unexplored factors related to blastocyst development and karyotype concordance may introduce potential biases and uncertainties in the results.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings demonstrate a cell lineage-specific effect of aneuploidy on the apoptotic levels and differentiation capacity of human blastocysts. This contributes to unravelling the biological characteristics of mosaic blastocysts and supports the concept of clonal depletion of aneuploid cells in explaining their reproductive potential.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by grants from Centro para el Desarrollo Tecnológico Industrial (CDTI) (20190022) and Generalitat Valenciana (APOTIP/2019/009). None of the authors has any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Automation in vitrification and thawing of mouse oocytes and embryos

Vitrification is a common technique for cryopreserving oocytes or embryos. However, manual vitrification is tedious and labor-intensive, and can be subject to variations caused by human factors. To address these challenges, we developed an automated vitrification-thawing system (AVTS) based on a cryo-handle. Our study firstly assessed the efficiency of cryoprotectant exchange through comparing the osmolalities of fresh and collected solutions during automated vitrification and thawing, and evaluated the cooling and warming rates of the cryo-handle. We also compared mouse oocyte survival, fertilization and embryo development after thawing and ICSI, and the development of re-frozen cleavage embryos between manual operation and automated system. The results showed that the osmolalities of collected samples were within normal range and comparable to fresh solutions. Furthermore, the automated system could obtain the reliable cooling and warming rates. Particularly, there were no significant differences in oocyte survival rates, fertilization rates, and subsequent embryo development and its quality between two procedures. Our findings suggest that AVTS has no impact on osmolalities of vitrification and thawing solutions, ensuring the proper exchange of cryoprotectants. The cryo-handle also shows the ability to achieve reliable cooling and warming rates, which benefits for the cryopreservation and thawing process. Moreover, the results from mouse oocytes and embryos indicate that automated system has effectively maintained the survival and fertilization of frozen oocytes and supported subsequent embryo development. Therefore, the automated vitrification and thawing system will inevitably represent a superior alternative to manual operation.

Mosaic results after preimplantation genetic testing for aneuploidy may be accompanied by changes in global gene expression

Aneuploidy in preimplantation embryos is a major cause of human reproductive failure. Unlike uniformly aneuploid embryos, embryos diagnosed as diploid-aneuploid mosaics after preimplantation genetic testing for aneuploidy (PGT-A) can develop into healthy infants. However, the reason why these embryos achieve full reproductive competence needs further research. Current RNA sequencing techniques allow for the investigation of the human preimplantation transcriptome, providing new insights into the molecular mechanisms of embryo development. In this prospective study, using euploid embryo gene expression as a control, we compared the transcriptome profiles of inner cell mass and trophectoderm samples from blastocysts with different levels of chromosomal mosaicism. A total of 25 samples were analyzed from 14 blastocysts with previous PGT-A diagnosis, including five low-level mosaic embryos and four high-level mosaic embryos. Global gene expression profiles visualized in cluster heatmaps were correlated with the original PGT-A diagnosis. In addition, gene expression distance based on the number of differentially expressed genes increased with the mosaic level, compared to euploid controls. Pathways involving apoptosis, mitosis, protein degradation, metabolism, and mitochondrial energy production were among the most deregulated within mosaic embryos. Retrospective analysis of the duration of blastomere cell cycles in mosaic embryos revealed several mitotic delays compared to euploid controls, providing additional evidence of the mosaic status. Overall, these findings suggest that embryos with mosaic results are not simply a misdiagnosis by-product, but may also have a genuine molecular identity that is compatible with their reproductive potential.

Mitochondrial DNA content decreases during in vitro human embryo development: insights into mitochondrial DNA variation in preimplantation embryos donated for research

OBJECTIVE

To assess the mitochondrial DNA (mtDNA) load and variation in human oocytes and during preimplantation embryo development using specimens donated for research.

DESIGN

Prospective cohort study.

SETTING

Not applicable.

PATIENTS

A total of 50 in vitro fertilization patients and 11 oocyte donors whose specimens were obtained between July 2017 and July 2018.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

All specimens were separately collected. Quantitative polymerase chain reaction was performed with SurePlex DNA Amplification System (Illumina). Primers for the adenosine triphosphate 8 mitochondrial gene and the β-actin were used. Data were statistically analyzed by analysis of variance with the Scheffé multiple pairwise comparison for categorical variables and by linear regression for numerical variables.

RESULTS

Human metaphase II (MII) oocytes had significantly more total mtDNA copy number than day 3 embryos, and day 3 embryos had more total and per-cell mtDNA copy number than aneuploid blastocysts. There was a significant decrease in mtDNA content associated with failed-fertilized oocytes compared to noninseminated metaphase II oocytes.

CONCLUSIONS

During preimplantation development, before implantation, human embryos undergo a significant decrease in total mtDNA content and no increase in mtDNA content at the blastocyst stage. Oocytes need to carry a correct threshold of mitochondrial load in the oocyte in order to successfully fertilize. An active degradation of mtDNA before implantation occurs after fertilization takes place. These findings could be used to improve knowledge about the best embryo culture conditions and would serve as a basis for further studies addressing again the use of mtDNA content as an embryo viability marker.

Conforming with current regulation in Turkey regarding the freezing of oocytes: A case report of the first pregnancy in Turkey achieved through oocyte vitrification

Objectives:

To present the first pregnancy achieved in Turkey with frozen–warmed oocytes in a case with previous nine unsuccessful assisted reproductive technology (ART) attempts.

Methods:

The clinical follow-up of a 33-year-old female applying to our ART centre after a long and complicated history of infertility is described.

Results:

In April 2013, the woman attempted our centre for her 10th ART trial. She informed us on oocyte pick-up (OPU) day that her husband had been hospitalized following a car crush in Albania and was unable to travel to our clinic to give a sperm sample. We were therefore placed in the position of having to make an emergency decision. OPU was done and seven oocytes were retrieved. Six metaphase II (MII) oocytes out of seven Cumulus Oocyte Complexes (COCs) were vitrified using the Kitazato Vitrification Cryotop Kit. Six months later, in November 2013, the patient applied for transfer. Two blastocysts were transferred and the ART trial resulted with a singleton pregnancy and the birth of a healthy new-born at term via cesarean section.

Conclusion:

Regulation Codes on Assisted Reproductive Procedures and Assisted Reproductive Technology Centres, published in the Official Gazette of the Republic of Turkey, on 6 March 2010 forbade the freezing of gonad cells and tissues except when essential for medical reasons and stated that this would be specified later. However, the Regulation Codes published in the Official Gazette of the Republic of Turkey, on 30 September 2014 provided no further clarification. Unfortunately, the wording of the regulations did not specifically address this unexpected emergency situation. However, we saw our decision to cryopreserve the oocytes as a valid interpretation of the regulations, bearing in mind also the requirement that sperm and oocyte in the IVF process must be those of a married couple. Turkish medicolegal regulations should be revised to increase the chances of more women taking advantage of the procedure to preserve their reproductive autonomy and to give guidance on what action may be taken in emergency situations.

[Female age - related fertility decline: Far from the myth of the "selfish working-girl" and the "right to have a child"]

OBJECTIVES

To study the social dimension of age-related female infertility through an analysis of three key themes: the personal life histories of infertile women over 40 years of age; representations of age and the desire to become pregnant after age 40; opinions of French legislations framing Assisted Reproductive Technologies, age limits, egg donation, and egg freezing for non-medical reasons.

METHODS

This qualitative sociological study was based on semi-structured interviews with infertile women over age 40 going through fertility treatments. The interviews contained three parts: personal and relationship histories; experiences related to age; opinions related to French legislation.

RESULTS

Twenty-three interviews were conducted; each lasting between 90 to 120minutes. Far from having similar life histories, the women interviewed had very different backgrounds leading to their desire for a pregnancy after 40 years of age. From the beginning of their fertility treatments, they perceived a "race against the clock". This feeling of urgency accompanied their experiences and was related to the desire to not be too old for their future child. The women interviewed were mainly in favor of loosening French bioethical laws in order to avoid the need to travel abroad to pursue fertility treatments.

CONCLUSION

The profiles studied attest to a growing gap between biological and biographical temporalities, as well as an inability of women to reduce their desire for a child. Faced with this disparity, egg donation and egg freezing were seen as practical solutions.

L’« horloge biologique » des femmes : un modèle naturaliste en question. Les normes et pratiques françaises face à la croissance de l’infertilité liée à l’âge

La croissance de l’infertilité liée à l’âge dans les sociétés industrielles avancées suscite un accroissement de demandes en matière d’assistance médicale à la procréation (AMP) et amène ainsi chaque société à s’interroger sur ses normes et pratiques. En France, cette question est un révélateur de la spécificité du modèle bioéthique qui encadre les techniques d’AMP ainsi que de ses tensions et contradictions croissantes. La particularité de ce modèle est de se présenter comme strictement « thérapeutique » et de reposer sur la notion d’« infertilité pathologique ». Or c’est justement la simplicité apparente de cette distinction entre pathologie et convenance que met en question l’infertilité liée à l’âge : elle ouvre vers une approche plus complexe de l’infertilité comme phénomène liant à la fois le somatique et le social. À partir d’une enquête auprès de professionnels qui font face à l’infertilité, nous montrerons la prégnance de ce modèle thérapeutique dans leur pratique. Mais nous verrons également que le contexte sociodémographique contemporain amène à une évolution de la notion même d’infertilité et interroge ce modèle de référence. De plus, l’apparition de nouvelles techniques telles que la congélation ovocytaire renforce la mise en question du modèle bioéthique et amène à penser autrement l’opposition pathologie/convenance sur laquelle il est construit. La question est de savoir si ce modèle saura évoluer vers une vision plus complexe et moins idéologique de l’infertilité, ce qui s’avère être un enjeu important pour la société française dans les années à venir et qui va bien au-delà de l’accès aux techniques favorisant ce dépassement.

Short-term storage of tripronucleated human embryos

PURPOSE

To determine the survival and subsequent in vitro development of human cleavage stage embryos and hatched blastocysts following varying periods of short-term storage at 4 °C, using tripronucleated human embryos (TPN) as a model.

METHODS

TPN cleavage embryos and hatched blastocysts short-term stored at 4 °C for 0 h (control), 24 h and 48 h. The main outcome measures were: survival rates (SR) and in vitro developmental ability (blastocyst rate and blastocyst-re-expansion rate) in each of the groups after storage.

RESULTS

Cleavage-stage TPN survived at comparable rates to controls, regardless of storage time (average: 97.3 %). The in vitro development of cleavage-stage TPN stored for 24 h was comparable to that of controls (average 64.7 %), but was significantly impaired when storage lasted 48-h (20.8 %). After artificial shrinkage, SR was comparable in 24-h-stored and non-stored hatched blastocysts (85.7 %; p > 0.05), but was significantly impaired in the 48-h-stored group (20.0 %). Following 24-h storage, the re-expansion rate of hatched blastocysts was similar to that of controls (average: 57.1 %; p > 0.05), but was higher than that of the 48-h-stored group (15.0 %; p < 0.05).

CONCLUSIONS

TPN human cleavage embryos and blastocysts can be successfully stored short-term for up to 24 h at 4 °C without using cryoprotectants without any significant negative impact on survival or subsequent in vitro development.