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.

Lessons learned from 64,071 embryos subjected to PGT for aneuploidies: results, recurrence pattern and indications analysis.

RESEARCH QUESTION: What is the influence of biological, technical and clinical factors on embryo outcomes in preimplantation genetic testing for aneuploidies (PGT-A) and what is the recurrence pattern? DESIGN: This retrospective study included 64,071 embryos undergoing PGT-A in the same laboratory between 2011 and 2019. Biopsies were performed at the day 3 embryo stage (48.32%) or blastocyst stage (51.70%). Advanced maternal age (AMA) was the main indication (65.62%). RESULTS: The aneuploidy rate was 67.75%, higher in women aged over 35 years than in women aged 35 years or less (71.76% versus 47.44%), and higher in day 3 embryo versus blastocyst biopsies (77.51% versus 58.62%). The trisomy:monosomy ratio was 1.01 for blastocysts versus 0.84 for day 3 embryos. Trisomy 21 was present in 4.9% of embryos. In aneuploid embryos, the probability of having one or more involved chromosomes followed a decreasing exponential pattern. The probability of an embryo being euploid was constant at around 30% (40% in blastocysts, 20% in day 3 embryos). The cumulative probability of having one or more euploid embryos after 10 biopsied embryos was 94.79% in blastocysts and 80.61% in day 3 embryos. AMA was associated with a much higher aneuploidy rate than all other indications, which among them had similar aneuploidy rate and chromosomal involvement. CONCLUSIONS: There is a considerably lower aneuploidy rate in blastocysts than day 3 embryos, which is most notable for monosomies. While AMA shows an increased aneuploidy rate and a specific chromosomal pattern of involvement, the remaining indications showed a similar aneuploidy rate and chromosomal pattern. Even after producing many consecutive aneuploid embryos, the possibility of obtaining a euploid embryo is not negligible.

The effect of vitrification on blastocyst mitochondrial DNA dynamics and gene expression profiles.

PURPOSE: Does vitrification/warming affect the mitochondrial DNA (mtDNA) content and the gene expression profile of blastocysts? METHODS: Prospective cohort study in which 89 blastocysts were obtained from 50 patients between July 2017 and August 2018. mtDNA was measured in a total of 71 aneuploid blastocysts by means of real-time polymerase chain reaction (RT-PCR). Transcriptomic analysis was performed by RNA sequencing (RNA-seq) in an additional 8 aneuploid blastocysts cultured for 0 h after warming, and 10 aneuploid blastocysts cultured for 4-5 h after warming. RESULTS: A significant decrease in mtDNA content just during the first hour after the warming process in blastocysts was found (P < 0.05). However, mtDNA content experimented a significantly increased along the later culture hours achieving the original mtDNA levels before vitrification after 4-5 h of culture (P < 0.05). Gene expression analysis and functional enrichment analysis revealed that such recovery was accompanied by upregulation of pathways associated with embryo developmental capacity and uterine embryo development. Interestingly, the significant increase in mtDNA content observed in blastocysts just after warming also coincided with the differential expression of several cellular stress response-related pathways, such as apoptosis, DNA damage, humoral immune responses, and cancer. CONCLUSION: To our knowledge, this is the first study demonstrating in humans, a modulation in blastocysts mtDNA content in response to vitrification and warming. These results will be useful in understanding which pathways and mechanisms may be activated in human blastocysts following vitrification and warming before a transfer.

Elevated serum progesterone does not impact euploidy rates in PGT-A patients.

PURPOSE: Some women undergoing stimulated cycles have elevated serum progesterone (P) on the day of ovulation trigger, but its effect on embryo quality is unclear. We analyze embryo quality among patients with high and low serum P undergoing preimplantation genetic testing for aneuploidy (PGT-A). METHODS: This retrospective study included 1597 patients divided into two groups by serum P values: < 1.5 ng/mL or ≥ 1.5 ng/mL. A gonadotrophin-releasing hormone (GnRH) antagonist protocol was established for each patient. Serum P levels were measured on the day of triggering. Propensity score matching and Poisson regression were done. Age, body mass index, and ovarian sensitivity index were also compared. RESULTS: Elevated serum P was not significantly associated with euploid embryo rate or other embryo-quality variables evaluated in our study. Age was the only variable associated with euploidy rate (per MII oocyte, P < 0.001; per biopsied embryo, P = 0.008), embryo biopsy rate (P < 0.001), absolute number of euploid embryos (P = 0.008), and top-quality embryo rate (P = 0.008). Categorical variables decreased in value for every year of increased age in patients with high serum P. CONCLUSIONS: Elevated serum P did not affect the number of euploid and good-quality embryos for transfer in GnRH antagonist intracytoplasmic sperm injection (ICSI) cycles. Contrary to the clear influence of premature P elevation on endometrial receptivity based on literature, our results may help to tip the balance towards the absence of a negative effect of P elevation on embryo competence. More studies are needed to fully understand the effect of P elevation on reproductive outcomes.

Sperm chromosomal abnormalities and their contribution to human embryo aneuploidy.

In this work we reviewed 18 years of experience using fluorescence in situ hybridization (FISH) for sperm aneuploidy testing. We evaluated parameters associated with increased numerical sperm chromosome abnormalities and determined the male contribution to embryo aneploidies in terms of reproductive outcome by increased sperm aneuploidy. This retrospective study analyzed data from 2008 sperm samples of infertile males undergoing FISH analysis because of clinical history of repetitive implantation failure, recurrent miscarriage, impaired sperm parameters, or mixed causes. Sperm concentration was the only sperm parameter associated with FISH results-we observed a gradual increase of abnormal sperm FISH results in males with decreasing sperm concentration. However, a great proportion of normozoospermic males also showed increased sperm aneuploidies, suggesting that sperm parameters alone do not enable identification of a substantial proportion of infertile males at risk of sperm aneuploidies. Regarding reproductive outcomes, couples with normal sperm FISH results for the male had similar outcomes regardless of conventional in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), or preimplantation genetic testing for aneuploidies (PGT-A). However, couples with abnormal sperm FISH results for the male showed better clinical outcomes after PGT-A, suggesting a potential contribution of sperm to embryo aneuploidy. Moreover, PGT-A cycles showed better clinical outcomes when 24 chromosomes were analyzed by array comparative genome hybridization (aCGH) or next-generation sequencing (NGS) instead of only nine chromosomes analyzed by FISH. In conclusion, sperm FISH analysis offers clinical prognostic value to evaluate reproductive possibilities in infertile couples. Therefore, couples with abnormal sperm FISH results should be offered genetic counseling and presented with clinical options such as PGT-A.

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.

False positive rate of an arrayCGH platform for single-cell preimplantation genetic screening and subsequent clinical application on day-3.

In this work, false positive rate of an arrayCGH platform for its use in day-3 single-blastomere analysis was calculated. For this purpose, 38 embryos diagnosed as abnormal on day-3 by FISH were re-biopsied on day-4. Single-cell day-4 arrayCGH diagnosis was then performed. A successful amplification was obtained in 97.4 % (37/38) of the day-4 cells analysed by arrayCGH. Day-3 FISH and day-4 arrayCGH diagnosis were concordant in 35/37 cases. The two discordant embryos were spread and all the cells from each embryo were re-analysed by FISH on day 5. The same error rate (2.7 %) for day-3 FISH and day-4 arrayCGH was obtained when comparing day-5 FISH re-analysis. After this pre-clinical phase, the platform was used for day-3 arrayCGH clinical application in 320 patients (1,760 embryos). Day-3 amplification rate was 98.6 %. An optimal reproductive outcome was obtained when applying arrayCGH to a clinical program: clinical pregnancy rate per cycle of 38.4 % and 60.3 % per transference were obtained, with an implantation rate of 53.5 %. Overall miscarriage rate was 10.6 %. Additionally, day-5 FISH re-analysis was performed in 42 of the embryos from the clinical phase, obtaining a concordance rate of 97.6 % with day-3 arrayCGH.

Spontaneous in vitro maturation and artificial activation of human germinal vesicle oocytes recovered from stimulated cycles.

PURPOSE: To define germinal vesicles (GV) by morphometric and morphologic examination and by chromatin compaction and to assess their spontaneous nuclear and cytoplasmic competence. MATERIALS: 131 GV were cultured for 42.7 ± 2.4 h. Nuclear maturation was evaluated at four time points. Sixty-seven in vitro and twenty-five in vivo metaphase II (MII) were activated. Parthenotes with 2 PB and one pronucleus (NA) were studied for ploidy. RESULTS: A total of 74.8% GV matured to MII: 55% at 21.4 ± 2.4 h and 47.3% in the following 24 h. Artificial activation induced NA in 79.2% of in vivo-MII and in 22.4% of in vitro-MII. All NA were haploid. CONCLUSIONS: GV spontaneously mature at the nuclear level. Their NA are haploid, but their cytoplasmic competence is compromised. Variables were not found to be predictors of oocyte competence, probably due to our population being homogeneous with respect to most of the variables studied.

The morphokinetic signature of mosaic embryos: evidence in support of their own genetic identity.

OBJECTIVE: To provide full morphokinetic characterization of embryos ranked with different degrees of chromosomal mosaicism. DESIGN: Retrospective cohort study. SETTING: University-affiliated private in vitro fertilization clinic. PATIENT(S): We analyzed 1,511 embryos from 424 intracytoplasmic sperm injection cycles by culturing embryos in a time-lapse imaging system and performing next-generation sequencing. We assessed 106 mosaic embryos. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Comparison of chromosomal, morphological, and morphokinetic characteristics of blastocysts classified as euploid, aneuploid, low-degree mosaic (30% to <50% aneuploid cells in trophectoderm biopsy), and high-degree mosaic (50% to <70% aneuploid cells in trophectoderm biopsy). Statistical analysis was performed using χ2, Kruskal-Wallis, or analysis of variance tests according to data type and distribution. A two-way random effects model was used to calculate interoperator correlation of annotations, and a logistic mixed effects model was performed to evaluate the effect of confounders on morphokinetic timing. RESULT(S): The mosaicism rate was ∼7% regardless of parental age. Mosaicism and uniform aneuploidies were not evenly distributed across chromosomes. The percentage of high-quality blastocysts significantly decreased from euploid (66.9%) to mosaic (52.8%) and aneuploid (47.7%). Aneuploid blastocysts significantly delayed development compared with euploid blastocysts in start of compaction (median, 84.72 hours postmicroinjection [hpm], interquartile range [IQR], 13.2; vs. median, 82.10 hpm, IQR, 11.5), start of blastulation (median, 101 hpm; IQR, 11.7; vs. median, 98.29 hpm, IQR, 10.5), and timing of blastocyst (median, 108.04 hpm, IQR, 11.50; vs. median, 104.71 hpm, IQR, 11.35). However, embryo morphokinetics were not correlated to the degree of mosaicism or to a mosaicism configuration that was apt for embryo transfer. CONCLUSION(S): Morphokinetic timing of mosaic embryos overlaps with that of euploid and aneuploid embryos, which may reflect their unique genetic and developmental identity. Although this suggests mosaic embryos are not simply a misdiagnosis by-product, further studies are needed to reveal the true identity of this particular type of embryo.

Prospective cohort study in high responder oocyte donors using two hormonal stimulation protocols: impact on embryo aneuploidy and development.

BACKGROUND: Ovarian stimulation regimens for in vitro fertilization seem to have a deleterious effect on oocyte quality and embryo aneuploidy in a dose-dependent manner. This study aims to test the influence of gonadotrophin doses on embryo aneuploidy rates. METHODS: A total of 32 young oocyte donors with a high response to ovarian stimulation, were included in the study. Two subsequent stimulation treatments were performed in each donor: first, a standard dose cycle using a 225 IU starting dose of recombinant FSH (r-FSH) and secondly, a reduced dose cycle with a starting dose of 150 IU r-FSH. In both cycles, GnRH agonist co-treatment was used for down-regulation. Ovarian response, embryo development and aneuploidy for chromosomes 13, 15, 16, 17, 18, 21, 22, X and Y were the main outcomes of the study. RESULTS: A total of 22 donors completed both treatments with different gonadotrophin doses. In the remaining 10 donors, the reduced dose cycle was cancelled due to low ovarian response. In those donors who completed both regimens, significant increases in rates of fertilization and chromosomally normal blastocysts were observed in the reduced dose cycle. No differences were observed in pregnancy and implantation rates in recipients who received oocytes from standard and reduced doses cycles. CONCLUSIONS: Despite the limited numbers in our study, we can conclude that in high responder donors, a decrease in the gonadotrophin dose could improve fertilization rates and embryo quality. However, due to the reduced oocyte numbers with lower doses, a similar reproductive outcome in terms of live births would be expected.

Redefining advanced maternal age as an indication for preimplantation genetic screening.

In this retrospective study, the utility of preimplantation genetic screening (PGS) in patients with advanced maternal age is evaluated. The patient population consisted of women aged 38-44years and included in a regular IVF programme with or without PGS analysis. Transfer rate, ongoing implantation rate and ongoing pregnancy rate were the main outcome parameters measured. A trend of better ongoing pregnancy rate per oocyte retrieval was observed in patients aged 38 and 39years in the non-PGS group when compared with PGS groups, but better ongoing pregnancy rate per oocyte retrieval was observed in patients 41-44years old in the PGS group. When patients with a low ovarian response accumulated oocytes in several stimulation cycles, clinical outcomes were comparable to those of normal-responder patients. These results show that, although PGS does not benefit patients less than 40years of age, reproductive success increases more than two-fold in patients over 40years, especially in patients with more than six metaphase II oocytes, as a result of a good ovarian response or gamete accumulation, suggesting a redefinition of advanced maternal age as indication for PGS. In this retrospective study, the utility of preimplantation genetic screening (PGS) in patients with advanced maternal age is evaluated. Patient population consisted of women aged 38-44 years and included in a regular IVF programme with or without PGS analysis. Transfer rate, ongoing implantation rate and ongoing pregnancy rate were the main outcome parameters measured. A trend of better ongoing pregnancy rate per ovarian stimulation cycle was observed in patients aged 38-39 years in the non-PGS group when compared with PGS groups, but better ongoing implantation rate was observed in patients aged 41-44 years old in the PGS group. When patients with a low ovarian response (low number of oocytes available for the IVF cycle) accumulated oocytes in several stimulation cycles, their reproductive possibilities were comparable to those of normal-responder patients. These results show that, although PGS does not benefit patients less than 40 years of age, reproductive success increases more than 2-fold in patients over 40 years, especially in patients with more than six metaphase II oocytes, as a result of a good ovarian response or gamete accumulation, suggesting a redefinition of advanced maternal age as indication for PGS.

Preimplantation genetic testing for aneuploidy in patients with partial X monosomy using their own oocytes: is this a suitable indication?

OBJECTIVE: To describe the outcome of preimplantation genetic testing (PGT-A) using their own oocytes in patients with mosaic Turner Syndrome (MTS). The impact of the assisted reproduction technique (ART) performed (PGT-A or oocyte donation) and the type of absence of the X chromosome (total or partial) were considered. DESIGN: Retrospective observational multicenter study. SETTING: University-affiliated private in vitro fertilization center. PATIENT(S): Fifty-six patients with MTS with whom 65 ovarian stimulation cycles for PGT-A (fluorescence in situ hybridization/arrays-next generation sequencing) were performed. The study included 90 women with MTS and 20 women with pure Turner Syndrome (PTS) who underwent 140 and 25 oocyte donation (OD) cycles, respectively. INTERVENTION(S): In vitro fertilization for PGT-A (fluorescence in situ hybridization/arrays-next generation sequencing) or OD. MAIN OUTCOME MEASURE (S): Reproductive outcome and feto-maternal outcomes. RESULTS: The live birth rate (LBR) per embryo transfer in patients with MTS tended to be higher in OD 37.7% (95% confidence interval [CI]: 29.3-46.1) than that observed for PGT-A 22.5% (95% CI 7.8-38.2), and the cumulative LBR (CLBR), with 77.6% vs. 43.3%, respectively. Likewise, the LBR per patient was significant when comparing PGT-A vs. OD, with 12.5% (95 CI 3.9-21.1) vs. 51.1% (40.7-61.4), respectively. While focusing on the X chromosome, partial MTS (PTS), we found significant differences in the CLBR per embryo transfer, with 77.6% vs. 29.2%, and also in the LBR per patient: 51.1% (40.7-61.4) in MTS vs. 15% (95 CI 0.0-30.1) in PTS. CONCLUSION(S): Oocyte donation is the best reproductive option in females with Turner Syndrome with or without mosaicisms. Nevertheless, PGT-A is a valid therapeutic option in patients with MTS using their own oocytes, and OD should not necessarily be directly recommended.

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 ß-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.

Prognostic factors for preimplantation genetic screening in repeated pregnancy loss.

The objective of this study was to identify specific subgroups of recurrent pregnancy loss (RPL) patients of unknown aetiology in whom the selection of chromosomally normal embryos for transfer improves reproductive outcome in preimplantation genetic screening (PGS). A total of 428 PGS cycles were included and chromosomes 13, 15, 16, 18, 21, 22, X and Y were evaluated. In RPL patients < or =37 years, a lower incidence of chromosomal abnormalities (P = 0.0004) and miscarriages (P = 0.0283) was observed, and there were significantly higher pregnancy (P < 0.0384) and implantation (P < 0.0434) rates than in patients >37 years. In the former subset, results showed: (i) significantly higher implantation rates (P = 0.0411) in couples that had experienced a previous aneuploid miscarriage; (ii) similar aneuploidy, pregnancy and implantation rates in couples suffering previous miscarriages during fertility treatments and in those with previous spontaneous pregnancies; (iii) no miscarriages after PGS in couples in whom a fluorescence in-situ hybridization assay showed the male partner's sperm to be abnormal; and (iv) lower implantation rates in couples with > or =5 previous miscarriages, associated with a lower percentage of chromosomally abnormal embryos. It is concluded that PGS is to be strongly recommended when RPL is associated with miscarriages during infertility treatments, chromosomopathy in a previous miscarriage, up to five previous miscarriages and a high incidence of chromosomal abnormalities in spermatozoa.

Transcriptomic behavior of genes associated with chromosome 21 aneuploidies in early embryo development.

OBJECTIVE: To analyze how chromosome 21 (HSA21) ploidy affects global gene expression of early human blastocysts. DESIGN: Prospective study. SETTING: University-affiliated in vitro fertilization clinic. PATIENT(S): A total of 26 high-quality donated embryos from in vitro fertilization (IVF) patients: trisomy 21 (n = 8), monosomy 21 (n = 10), and euploid (n = 8) blastocysts. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Blastocyst transcriptome changes and its associated functions. RESULT(S): Trisomy 21, monosomy 21, and euploid blastocysts were classified by comparative genomic hybridization. The global transcriptome of whole blastocysts was analyzed with small cell number RNA sequencing, and they were compared to understand the gene expression behavior at early development and its implications for embryo implantation. We identified 1,232 differentially expressed genes (false discovery rate <0.05) in monosomy 21 compared with euploid blastocysts associated with dysregulated functions in embryo development as the Rap1 signaling pathway. Curiously, Down syndrome in early development revealed fewer transcriptomic changes than expected. In addition, Down syndrome gene expression in neonates, children, and adults revealed that the number of deregulated genes increases across life stages from blastocysts to adults, suggesting a potential dosage-compensation mechanism for human chromosome 21. CONCLUSION(S): At the transcriptomic level, early development in Down syndrome is mainly dosage compensated. However, monosomy 21 is strongly transcriptionally affected because early development involving main functions is associated with embryo implantation.

Variables associated with mitochondrial copy number in human blastocysts: what can we learn from trophectoderm biopsies?

OBJECTIVE: To study the potential variables that affect the mitochondrial DNA (mtDNA) content of trophectoderm (TE) cells in blastocysts that have undergone TE biopsy. DESIGN: Observational retrospective single-center analysis. SETTING: University-affiliated private in vitro fertilization center. PATIENT(S): A total of 465 consecutive preimplantation genetic screening (PGS) cycles of 402 women undergoing preimplantation genetic testing. INTERVENTION(S): Trophectoderm biopsy performed on blastocysts of women undergoing preimplantation genetic testing-aneuploidy (PGT-A). MAIN OUTCOME MEASURE(S): The mtDNA content in trophectoderm cells. RESULT(S): We checked the possible influence of patient characteristics, ovarian stimulation variables, embryo morphology, and embryo culture conditions on mtDNA values. Of all the analyzed variables, some such as body mass index (BMI), serum progesterone (P4), aneuploidy, and trophectoderm quality had an effect on mtDNA content in blastocysts. Body mass index had a small but positive effect on the mtDNA copy number; as the BMI values increased, the probability of women producing blastocysts with an mtDNA content above the median increased by 6%. For P4 serum concentration, an increase in P4 lowered the probability of blastocysts having values above the median by 39%. Embryo-associated variables such as TE quality and aneuploidy status appeared to affect the mtDNA copy number. For the aneuploid blastocysts, the probability of being above the median increased by 42%. Finally, blastocysts with poor quality TE had more chances of carrying higher mtDNA values. CONCLUSION(S): Summarizing, larger quantities of mtDNA in blastocysts are associated with the condition of aneuploidy and low quality TE, as well as being from women with high BMI values. Understanding the biological meaning of mtDNA content in human blastocysts and what factors may interfere with their values is fundamental. Other key gaps, such as whether a correlation exists between mtDNA content and mitochondrial mass and biogenesis in human TE cells, and whether this correlation can be extended to the inner cell mass, need to be further addressed. These questions are currently being investigated.

A Higher Ovarian Response after Stimulation for IVF Is Related to a Higher Number of Euploid Embryos.

This study has analysed the relationship between ovarian response and the number of euploid embryos. This is a post hoc analysis of a subset of data generated during a prospective cohort study previously published. Forty-six oocyte donors were subjected to ovarian stimulation with 150 IU of rFSH and 75 IU of hp-hMG in a GnRH agonist long protocol. Preimplantation genetic screening was performed in all viable embryos. We observed a positive relationship between ovarian response and the number of euploid embryos. When ovarian response was above the median (≥17 oocytes), the mean number of euploid embryos per donor was 5.0 ± 2.4, while when <17 oocytes were obtained the mean number of euploid embryos was 2.7 ± 1.4 (p = 0.000). Aneuploidy rate did not increase with ovarian response or gonadotropin doses. Also, the number of euploid embryos was inversely related to the amount of gonadotropins needed per oocyte obtained (ovarian sensitivity index). These results suggest that the number of euploid embryos available for embryo transfer increases as the number of oocytes obtained does. Considering the total number of euploid embryos seems more relevant than the aneuploidy rate.

Corrigendum to "A Higher Ovarian Response after Stimulation for IVF Is Related to a Higher Number of Euploid Embryos".

[This corrects the article DOI: 10.1155/2017/5637923.].

Human embryo culture.

Human embryonic stem cells (hESCs) are derived from preimplantation embryos. Approximately 60% of human embryos are blocked during in vitro development. Although statistics are inconclusive, experience demonstrates that hESCs are more effectively derived from high-quality embryos. In this way, optimal human embryo culture conditions are a crucial aspect in any derivation laboratory. Embryos can be cultured solely with sequential media or cocultured on a monolayer of a given cell type. This chapter explores general aspects of human embryonic development, the concept of sequential culture and coculture, and specific protocols and procedures in which the authors are experienced, including the results obtained.

Distribution patterns of segmental aneuploidies in human blastocysts identified by next-generation sequencing.

OBJECTIVE: To evaluate the ability of next-generation sequencing (NGS) to detect pure and mosaic segmental aneuploidies in trophectoderm biopsies and to identify distribution patterns in whole blastocysts. DESIGN: Validation study. SETTING: Reference laboratory. PATIENT(S): Seventy couples with known karyotypes who had undergone preimplantation genetic screening with diagnoses at the blastocyst stage using array comparative genomic hybridization (aCGH). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Concordance rates for segmental and whole-chromosome aneuploidies determined between aCGH and NGS, and estimates of mosaicism levels of segmental aneuploidies in fixed blastocysts. RESULT(S): We used NGS with amplified DNA from trophectoderm biopsies in which segmental aneuploidies had been previously detected by array comparative genomic hybridization (aCGH). Single-cell fluorescent in situ hybridization (FISH) was then used as an independent form of analysis. The concordance rate between NGS and aCGH was 124 (98.4%) of 126 for the detection of segmental aneuploidies, and 48 (96.0%) of 50 for whole-chromosome aneuploidies. The overall concordance rate was 99.8% (2,276 of 2,280 chromosomes assessed). After FISH analyses with 41.4 ± 24.3 cells per blastocyst, 26 (92.9%) of 28 segmentals detected by aCGH and NGS were confirmed. The FISH analysis did not detect the segmentals in two blastocysts, in which all cells analyzed were euploid. CONCLUSION(S): This is the first report analyzing distribution patterns of segmental aneuploidies in trophectoderm biopsy by NGS. We have demonstrated that NGS allows the detection of pure and mosaic segmental aneuploidies with the same efficiency as aCGH. The FISH analysis confirmed the existence of these events in the trophectoderm and the inner cell mass.