Kinetic characteristics of mosaic embryos observed by time-lapse and their post-implantation outcomes: A single-center retrospective cohort study
Article information
Abstract
Objective
The interpretation and evaluation of mosaicism in pre-implantation genetic testing for aneuploidy (PGT-A) are complex, and no consensus or standardized criteria are currently available. We investigated whether mosaicism, as assessed by type or level in PGT-A, is correlated with clinical pregnancy and live birth rates.
Methods
This retrospective experimental trial included 207 oocyte retrieval cycles and 124 cycles of single vitrified-warmed blastocyst transfer performed between August 2020 and March 2023 at a single in vitro fertilization center. A total of 124 single vitrified-warmed blastocyst transfer cycles were analyzed for clinical outcomes, stratified by mosaic type and level. We also analyzed the correlations between kinetic characteristics and embryo ploidy.
Results
No significant difference in live birth rates was found between the euploid and low-level mosaic groups (52.9% vs. 35.7%). However, live birth rates were significantly lower in the high-level mosaic group than in the euploid group (52.9% vs. 17.6%, p<0.05). No full-term live births were recorded among the embryos with high-level mosaicism for trisomy and segmental aneuploidy, although three live births were observed in high-level mosaic embryos with monosomy. Furthermore, time to blastocyst development was longer in mosaic embryos than in euploid embryos. However, when analyzed according to mosaic level, the developmental kinetics were not sufficiently distinctive to enable reliable non-invasive prediction of mosaic status.
Conclusion
This study suggests that ranking embryos by the level and type of mosaicism can help maximize post-implantation outcomes. Live birth rates varied according to the type of mosaicism.
Introduction
In assisted reproductive technology (ART), multiple births have historically been a serious problem resulting from the transfer of two or more embryos into the uterus [1,2]. Modern ART clinics now aim to achieve a healthy live birth using single embryo transfer. In recent years, culture media and culture conditions have advanced dramatically, and embryos cultured in vitro for 5 to 6 days frequently yield several blastocysts for transfer [3]. In such situations, the issue arises as to how best to rank embryo quality to achieve a successful pregnancy. Pre-implantation genetic testing for aneuploidy (PGT-A) is a technique used to select high-quality embryos by assessing the chromosome number of multiple blastocysts [4]. In embryo selection, normal chromosome composition, as defined by PGT-A, is the strongest predictor of a successful pregnancy. However, PGT-A also detects chromosomal mosaicism, in addition to euploidy and aneuploidy [5,6]. Exclusion of mosaic blastocysts can reduce the number of embryos available for transfer, which may lead to poor outcomes. Chromosomal mosaicism refers to the presence of a mixture of euploid and aneuploid cells, a condition arising from mitotic errors [7]. The interpretation and assessment of mosaicism in embryos are complex, and no consensus or standardized criteria are currently available for its evaluation. The incidence of mosaicism varies by embryonic stage, with reported rates of 4% to 22% at the blastocyst stage, depending on the clinic [8,9]. Although earlier PGT-A techniques had limited capacity to detect mosaicism, next-generation sequencing (NGS) is now widely used as a more accurate method for this purpose [10]. Viotti et al. [11] retrospectively analyzed 1,000 mosaic embryo transfers and found that pregnancy and live birth rates differed progressively according to the type and extent of mosaicism.
These findings suggest that the outcome of mosaic embryo transfer depends on the characteristics of mosaicism. Viotti et al. [11] focused on implantation rates, ongoing pregnancy rates, and live birth rates after mosaic embryo transfer, demonstrating the influence of mosaic status (number of chromosomes showing whole chromosome or segmental mosaicism). Several studies of mosaic trisomy and monosomy have shown that mosaic trisomy is associated with a higher risk of miscarriage than mosaic monosomy [9,12-17]. Furthermore, mosaicism involving multiple chromosomes has been associated with lower ongoing implantation rates than mosaicism involving one or two chromosomes [18-20]. Assessing mosaic embryos according to the type and level of mosaicism is therefore crucial for maximizing the clinical outcomes of PGT-A and increasing the chances of implantation.
The recent spread of time-lapse imaging has prompted the development of algorithms that combine PGT-A and morphokinetics to predict embryo ploidy [21]. These algorithms may be useful as a tool to predict ploidy non-invasively. Aneuploid embryos are known to develop more slowly than euploid embryos, but the comparative development of mosaic embryos is not fully understood [22]. Furthermore, high-level mosaic embryos are associated with developmental delay [23]. These findings suggest the possibility of non-invasively detecting mosaic embryos using information obtained from time-lapse imaging. Therefore, analyzing the relationship between the chromosomal status of embryos obtained by PGT-A and the timing of blastocyst development could clarify the impact of mitotic aneuploidies on embryo development.
The purpose of this study was to investigate implantable mosaic embryos and to retrospectively analyze implantation outcomes according to mosaic type and level. As a secondary objective, the kinetic characteristics of mosaic embryos were also examined using time-lapse imaging.
Methods
1. Patients and study design
This retrospective experimental trial included 207 oocyte retrieval cycles and 124 cycles of single vitrified-warmed blastocyst transfer performed between August 2020 and March 2023 at a single in vitro fertilization (IVF) center (Kinutani Women’s Clinic). A total of 557 blastocysts underwent PGT-A. All embryos were monitored using a time-lapse system from fertilization to the blastocyst stage. However, cases exhibiting structural chromosomal rearrangements on pre-implantation genetic testing and multiple embryo transfers, including two-step embryo transfers, were excluded from the analysis. The main outcome measures were clinical pregnancy (presence or absence of a gestational sac) and live birth. This study was approved by the Ethics Committee of Kinutani Women’s Clinic (certification number: 17000119). The approval number assigned to this study by the Institutional Review Board was 20191120. All procedures were conducted in accordance with the ethical standards of the institutional research committee and the 1964 Helsinki Declaration and its later amendments. Informed consent was obtained from all patients who participated in the study.
2. Ovarian stimulation and oocyte retrieval
Standard regimens of controlled ovarian hyperstimulation were employed based on established clinical protocols. Patients were treated with a gonadotropin-releasing hormone (GnRH) agonist using a short or long protocol following progestin-primed ovarian stimulation, in accordance with each patient’s ovarian response and medical history of IVF treatment. Serum estradiol levels were monitored, and follicular growth was evaluated by transvaginal ultrasonography. In some cycles, a minimal stimulation protocol or a natural cycle was used. When a follicle reached a mean diameter ≥18 mm, human chorionic gonadotropin (Aska Pharmaceutical), 250 g of choriogonadotropin alpha (Ovidrel; Merck Serono), or a GnRH agonist was administered. Transvaginal oocyte retrieval was performed 35 to 37 hours after administration.
3. Fertilization procedure and embryo culture
The retrieved cumulus–oocyte complexes were cultured for approximately 4 hours in G-IVF medium (Vitrolife) at 37 °C under an atmosphere of 6% CO2, 5% O2, and 89% N2 before conventional IVF (c-IVF) or intracytoplasmic sperm injection (ICSI). For c-IVF, sperm was prepared at a concentration of 7.5–10×106/mL. A total of 5 to 50 μL of sperm was added to the dish containing the oocytes. The sperm and oocytes were then co-cultured at 37 ºC under 6% CO2, 5% O2, and 89% N2 for approximately 18 to 20 hours. For ICSI, cumulus–oocyte complexes were denuded via pipetting with 80 IU/mL hyaluronidase (Irvine Scientific). The maturity of denuded oocytes was assessed by visualization of the first polar body. Only metaphase II oocytes were used for ICSI. Embryos fertilized by c-IVF or ICSI were cultured in DNP dishes (Dai Nippon Printing Co. Ltd.) with SAGE™ 1-Step (Origio) at 37 °C under an atmosphere of 6% CO2, 5% O2, and 89% N2 for 5 to 7 days and evaluated for development to the blastocyst stage.
4. Blastocyst biopsy protocols, NGS analysis, and mosaicism classification
Trophectoderm (TE) biopsy was conducted on expanded blastocysts on days 5 to 7, regardless of morphological grade. First, artificial shrinkage was performed using a laser system (Zilos-TK; Hamilton Thorne Biosciences Inc.) to create a space between the zona pellucida and TE cells. While securing the blastocyst with the inner cell mass (ICM) positioned at approximately 8 to 9 o’clock, serial laser pulses were used to create a small hole (approximately 10 µm) in the zona pellucida at a position of approximately 3 to 4 o’clock. A biopsy pipette was then inserted into the hole created by the laser to aspirate the TE cells. Five to 10 TE cells were aspirated into the biopsy pipette and collected by flicking the holding pipette and biopsy pipette with the aid of several laser pulses. Biopsy samples were processed for whole-genome amplification and NGS at the Varinos Laboratory using the VeriSeq PGS kit (Illumina K.K.) on a MiSeq system (Illumina K.K.) in 24-sample runs, according to the manufacturer’s protocol. The copy number of each sample was analyzed using BluFuse Multi Software (Illumina K.K.). A molecular karyotype profile consistent with mosaicism was defined when a whole chromosome or chromosomal segment showed intermediate copy number levels of 20% to 80% between whole-number states, according to the guidelines of the Preimplantation Genetic Diagnosis International Society [24]. The mosaic embryo group was subclassified into low-level (between 20% and 49% abnormal cells) and high-level (between 50% and 80% abnormal cells) mosaicism. Mosaic embryos were further subgrouped into whole chromosome (loss or gain), segmental, and complex mosaic embryos. When mosaicism was present on more than one chromosome, the chromosome with the highest level of mosaicism was assigned as the mosaic type.
5. Vitrification and warming of blastocysts and embryo transfer
Blastocyst vitrification was performed as reported by Hiraoka et al. [25] within 1 hour after embryo biopsy. Blastocysts were placed in an equilibration solution containing 7.5% (v/v) ethylene glycol (Sigma-Aldrich) and 7.5% (v/v) dimethyl sulfoxide (Nacalai Tesque Inc.) in modified human tubal fluid (mHTF; Irvine Scientific) with 20% (v/v) serum protein substitute (SPS; Origio) at 37 °C. Blastocysts were then transferred into a vitrification solution containing 15% (v/v) ethylene glycol, 15% (v/v) dimethyl sulfoxide, and 0.5 M sucrose (Sigma-Aldrich) in mHTF with 20% SPS for 1 minute at 37 °C. Blastocysts were loaded onto Cryotops (Kitazato Corporation) in a minimal volume and immediately immersed in liquid nitrogen at –196 °C. For the warming protocol, the tip of the Cryotop was immersed directly in 1.0 M sucrose solution for 1 minute at 37 °C. Blastocysts were then transferred to 0.5 M sucrose solution for 3 minutes and washed twice in mHTF with 20% SPS for 5 minutes at 37 °C. Prior to embryo transfer, the warmed blastocyst was cultured for approximately 3 to 4 hours in EmbryoGlue (Vitrolife). Luteal phase support was started using intravaginal micronized progesterone or in natural cycles. Embryo transfers were performed under ultrasound guidance using a soft catheter (Origio).
6. Time-lapse assessment
Oocytes were cultured individually in a time-lapse system (CCM-iBIS; Astec). A total of 1 to 25 embryos were placed in a 100 µL drop of medium, and images of the embryos were recorded automatically at 15-minute intervals. Kinetic timing and compaction dynamics were annotated by two well-trained embryologists, who were blinded to the PGT-A results, using a Linkid image analyzer (Astec). The exact timing of two events was annotated as follows: completion of the compaction process (tM) and formation of a full blastocyst (tB). All timing parameters were expressed in hours after the fading of the pronucleus. Compaction was observed and classified into two patterns: ‘whole,’ indicating compaction through normal development, and ‘partial,’ indicating blastomeres left behind during compaction. In addition, an instrument was used to measure the diameter of the blastocyst at the time of embryo biopsy.
7. Statistical analysis
Statistical analysis was performed using JMP ver. 14.0 (SAS Institute Inc.) and GraphPad Prism ver. 6.03 (GraphPad Inc.). Patient characteristics were presented as mean and standard deviation. Proportions were analyzed using the Fisher exact probability test or the chi-square test to determine statistical differences. Continuous variables were compared using the Student t-test or one-way analysis of variance, and significance was determined using the Tukey–Kramer test. As the time-lapse data were not normally distributed, we used the Wilcoxon rank-sum test or Kruskal–Wallis test, and significance was determined using the Dunn test. To adjust for the potential confounding effect of maternal age on developmental kinetics, analysis of covariance (ANCOVA) was performed with maternal age included as a covariate. Differences were considered statistically significant at p<0.05.
Results
1. Participant characteristics
Table 1 shows the participant characteristics for oocyte retrieval cycles and NGS PGT-A results. Overall, 687 blastocysts were obtained from 207 oocyte retrieval cycles. Of these 687 blastocysts, 641 were biopsied and 578 were analyzed by NGS. The results revealed that 105 embryos were euploid and 364 were aneuploid. There were 88 embryos with mosaicism, categorized as low- or high-level according to the proportion of abnormal cells detected. All NGS-tested samples were subjected to ploidy analysis, and 16 embryos were found to have abnormal ploidy (haploidy or triploidy). In addition, 0.9% (five embryos) had inconclusive or failed NGS results. Table 2 shows the characteristics of embryo transfer participants. A total of 124 single vitrified-warmed blastocyst transfers were performed with euploid and mosaic embryos, primarily under hormone replacement cycles. Of these 124 cycles, 60 clinical pregnancies were achieved, 50 of which resulted in live births.
Participant characteristics regarding oocyte retrieval cycles and NGS preimplantation genetic testing for aneuploidy
Characteristics of participants regarding embryo transfer
2. Kinetic characteristics of mosaic embryos observed by time-lapse monitoring
The characteristics of PGT-A embryos observed by time-lapse are shown in Table 3. Maternal age in the euploid group was significantly lower than in the mosaic and aneuploid groups (37.3±3.79 years vs. 39.1±3.31 years vs. 40.6±3.08 years, respectively; p<0.05). However, paternal age was highest in the aneuploid group and did not differ significantly between the euploid and mosaic groups (38.8±4.92 years vs. 38.9±5.00 years vs. 42.1±5.34 years, respectively; p<0.05). Time to completion of compaction did not differ significantly among the three groups. Time to blastocyst development was earliest in the euploid group compared with the mosaic and aneuploid groups (83.3 hours [range, 69.0–111.7] vs. 87.3 hours [range, 71.5–120.8] vs. 88.2 hours [range, 71.0–139.0], respectively; p<0.05). The percentage of good-quality embryos decreased significantly in the order of euploid, mosaic, and aneuploid (61.9% vs. 43.2% vs. 25.8%, p<0.05), while the percentage of poor-quality embryos was highest in the aneuploid group (15.2% vs. 25.0% vs. 33.2%, respectively; p<0.05). ANCOVA was performed with maternal age as a covariate to adjust for potential age-related effects on blastocyst development. The effect of ploidy remained statistically significant (F=7.53, p=0.0006), whereas maternal age showed no significant association (F=1.90, p=0.168). These results indicate that differences in blastocyst development timing among euploid, mosaic, and aneuploid embryos are independent of maternal age. Figure 1 shows the timing of blastocyst development according to mosaic level. No significant difference was noted in the timing of compaction among the mosaic groups (euploid, 63.8 hours [range, 45.6–97.7]; low-level mosaic, 66.2 hours [range, 39.1–88.0]; high-level mosaic, 64.4 hours [range, 49.8–90.3]; aneuploid, 66.5 hours [range, 33.3–105.2]; not significant) (Figure 1A). Blastocyst development was significantly faster in the euploid group than in the aneuploid group (83.3 hours [range, 69.0–111.7] vs. 88.2 hours [range, 71.0–139.0]; p<0.01) (Figure 1B). However, no significant difference was found in the timing of blastocyst development between low- and high-level mosaicism (87.3 hours [range, 72.9–120.8] vs. 89.1 hours [range, 71.5–118.4], respectively; not significant) (Figure 1B). Mosaic embryos exhibited blastocyst development patterns intermediate between euploid and aneuploid embryos, but no significant differences were observed between the mosaic subgroups after subdivision by mosaicism level. Overall, differences in developmental kinetics and morphological grades were evident between the euploid and aneuploid embryos, whereas the kinetics of mosaic embryos resembled those of aneuploid embryos.
Timing to compaction and timing to blastocyst for PGT-A embryos observed by time-lapse monitoring
Distribution of timing of compaction completion and blastocyst development (from pronuclear fading to full blastocyst). Box plot of the timing of compaction in the euploid, low-level mosaic, high-level mosaic, and aneuploid groups (A). Box plot of the timing of blastocyst formation in the euploid, low-level mosaic, high-level mosaic, and aneuploid groups (B). Box plots show the median, first and third quartiles, minimum, maximum, and mean values (cross). Wilcoxon rank-sum tests and Bonferroni multiple comparison tests were used. NS, not significant.
3. Effect of mosaic type and level on clinical outcome
The PGT-A results for 124 cycles, including 71 mosaic embryos, were classified by mosaic type and level. Figure 2 shows the clinical outcomes after single vitrified-warmed blastocyst transfer stratified by mosaic type and level. Embryos with low-level mosaicism were classified into four types and analyzed for clinical outcomes. Pregnancy and live birth rates were highest for embryos with segmental mosaicism, but no statistically significant differences were found among mosaic types (Figure 2A, 2B). High-level mosaic embryos were separated into four categories, and the clinical pregnancy and live birth rates of these categories were compared (Figure 2C, 2D). Clinical pregnancies were observed even in mosaic embryos with high degrees of chromosomal mosaicism. The live birth rate for embryos with high-level chromosome loss (monosomy) was 37.5% (3/8). However, no full-term live births were recorded in the group showing high-level chromosomal gain (trisomy) or segmental aneuploidy. Clinical outcomes differed depending on whether the mosaicism involved monosomy or trisomy (Figure 2C, 2D).
Effect of mosaicism level and type on clinical outcome. Comparison of pregnancy rate (A) and live birth rate (B) among the low-level segmental mosaic, low-level mosaic gain, low-level mosaic loss, and low-level complex mosaic embryos. Comparison of pregnancy rate (C) and live birth rate (D) among the high-level mosaic loss, high-level mosaic gain, and segmental aneuploidy embryos. Fisher exact tests and Bonferroni multiple comparison tests were used. NS, not significant.
4. Neonatal outcomes stratified by mosaic group
Table 4 compares neonatal outcomes after single vitrified-warmed blastocyst transfer according to mosaic group. Neonatal outcomes were divided into three groups: euploid, low-level mosaicism, and high-level mosaicism. No significant differences were observed in clinical pregnancy rates among these groups. Miscarriage rates were significantly higher in the low-level and high-level mosaic groups than in the euploid group (euploid, 0% [0/27]; low-level mosaic, 33.3% [5/25]; high-level mosaic, 62.5% [5/8]; p<0.05). The live birth rate in the high-level mosaic group was 17.6% (3/17), significantly lower than that of the fully euploid embryos (52.9% [27/51]). No significant differences in beta-human chorionic gonadotropin levels or maternal age were found. Furthermore, no significant differences in mean birth weight were noted among the groups (euploid, 3,117±373.5 g; low-level mosaic, 3,073±502.0 g; high-level mosaic, 2,621±730.9 g).
Neonatal outcomes stratified by mosaic group
Discussion
This study examined implantable mosaic embryos by analyzing implantation outcomes according to mosaic type and level. In addition, the kinetic characteristics of mosaic embryos were evaluated. PGT-A is used to assess embryo aneuploidy to increase pregnancy rates, reduce miscarriage rates, and prioritize the highest-quality embryos for implantation. In this study, 50 healthy children were born from embryos in 124 PGT-A cycles, including cycles with mosaic embryos.
The possibility that viable embryos may be discarded because of concerns about mosaicism is a major challenge currently associated with PGT-A. The transfer of embryos classified as mosaic by PGT-A was first reported in 2015 and is now routine in clinical practice [26]. The reproductive potential of mosaic embryos remains a subject of debate [13,27]. When mosaic status is analyzed using techniques such as amplification or NGS, noise or artifacts may make it difficult to distinguish true mosaicism [28]. However, several studies have suggested that embryos classified as mosaic have reduced reproductive potential compared with embryos classified as euploid [9,19,29]. In these studies, diagnosis was primarily based on the presence or absence of mosaicism. The general definition of a mosaic embryo does not involve stringent thresholds (mosaicism: 20% to 80%), and it remains unclear which type or level of mosaicism is suitable for implantation [24].
Girardi et al. [30] found that, to maximize the accuracy of PGT-A, a single TE biopsy result should be reported according to a euploid/aneuploid classification based on a single cut-off of 50%. In this study, neonatal outcomes were divided into three groups using a 50% mosaicism threshold and compared. A slight decrease in live birth rate was observed from the euploid group to the low-level mosaic group, but this finding was not significant. Low-level mosaicism has been shown to resolve in subsequent TE biopsies, with many embryos later identified as uniformly euploid [31]. The incidence of chromosomal mosaicism also raises concerns that a significant proportion of PGT-A results may represent false-positive errors [32]. If the level of mosaicism is less than 50%, the developmental potential of the embryo may be similar to that of a euploid embryo. The live birth rate was significantly lower in the group with high-level mosaicism (17.6%) compared with 52.9% in the euploid group. Interestingly, no live births were recorded in the group with high-level chromosomal mosaicism or segmental aneuploidy. These results may differ depending on whether the embryos exhibit monosomy or trisomy. TE biopsy results do not always match the chromosomal composition of the ICM in mosaic embryos [33]. If TE biopsy shows more than 50% mosaicism and trisomy mosaicism, the chromosomal composition of most of these embryos is uniformly aneuploid [34]. Previous studies have shown that implantation is possible when trisomy abnormalities are present in the ICM, but miscarriage occurs in most cases [35].
Furthermore, segmental aneuploidy results from double-strand DNA breaks caused by endogenous and exogenous factors [36]. Segmental aneuploidy is often associated with mitotic errors and can lead to chromosomal mosaicism. Some studies suggest that embryos with segmental aneuploidy are more likely to contain aneuploid cells in the ICM, which contributes to pregnancy loss or implantation failure [9]. Even if these embryos are transferred, they face an increased risk of miscarriage due to chromosomal instability. Mosaic embryos clearly have greater developmental potential than uniformly aneuploid embryos, but embryos with severe trisomy or segmental aneuploidy are not suitable for transfer.
In this study, regardless of maternal age, mosaic and aneuploid embryos exhibited a significantly delayed time to blastocyst formation compared with euploid embryos. Few reports have examined the dynamics of mosaic embryos, although existing data suggest the potential for non-invasive identification of mosaic embryos [23,37]. However, when mosaic embryos were further classified by mosaic level, the dynamic parameters did not demonstrate sufficient discriminatory power to predict mosaic status. The delayed blastocyst formation observed in aneuploid embryos is consistent with previous reports and supports the concept that chromosomal abnormalities are associated with slower developmental dynamics [38]. TE biopsies are currently performed at the blastocyst stage because the incidence of mosaicism decreases between day 3 (cleavage stage) and day 5 (blastocyst stage) [39], likely due to self-corrective mechanisms during the cell division process [22]. In human embryos, aneuploid cells are sequestered from the ICM between day 3 and day 5 and are partially localized to the TE surrounding the blastocyst [40]. Although a comprehensive analysis of neonatal outcome data from transferred mosaic embryos is still required, 23 healthy newborns were born from the mosaic group in this investigation.
The main strength of this study lies in its comprehensive evaluation of mosaic embryos using both clinical outcome data and time-lapse dynamic analysis, combined with detailed classification based on mosaic type and level. Furthermore, this research included neonatal outcome data from mosaic embryos, revealing differences according to the level of mosaicism. However, this study also has several limitations. First, the relatively small sample size may limit statistical power, particularly in subgroup analyses of mosaic type. Second, the use of a retrospective study design and a single-center cohort may introduce selection bias. Furthermore, the interpretation of mosaicism based on PGT-A results is inherently constrained by technical and biological variability in the testing process. NGS analysis cannot always distinguish background noise or amplification artifacts from true mosaicism, and the chromosomal constitution of the TE biopsy may not fully reflect that of the ICM. These limitations may lead to potential misclassification of mosaic embryos, particularly at moderate levels of mosaicism, and may partly explain the variability in clinical outcomes between different mosaicism categories. Therefore, the results of this study should be interpreted with caution, recognizing the inherent uncertainty in the current diagnostic methods for detecting embryonic mosaicism.
To rank the suitability of mosaic embryos for transfer and to use them as a tool to increase the likelihood of a good clinical outcome, an algorithm incorporating the morphological and kinetic characteristics of the embryos should be developed. Most of the blastocysts used for transfer in this study were day 5 blastocysts with good morphology (≥BB). Blastocysts that were late in reaching this stage or had poor morphology were more likely to be aneuploid and therefore not selected for transfer. Currently, obvious chromosomal abnormalities such as mosaicism and chromosomal imbalance can only be detected by PGT-A, but the live birth rate of embryos transferred after PGT-A was only about 40% in this study. In ART, it is important to generate many embryos with high developmental potential. In conclusion, this study suggests that ranking embryos by the level and type of mosaicism can help maximize post-implantation outcomes. Embryos with segmental aneuploidy and high chromosomal mosaicism are not suitable for embryo transfer. Further research is required to gain a more complete understanding of whether mosaic embryos are associated with clinical pregnancy and live birth.
Notes
Conflict of interest
No potential conflict of interest relevant to this article was reported.
Acknowledgments
The authors thank the embryologist team at Kinutani Women’s Clinic for the data acquisition, as well as the participating couples and gynecologists at the infertility clinic. We also thank Varinos Inc. (https://varinos.com) CEO Yoshiyuki Sakuraba for his assistance with this paper.
Author contributions
Conceptualization: YH. Methodology: YH. Formal analysis: YH, EF, TM, HS, MI, RS, SO, MK. Data curation: YH, EF, TM, HS, MI, RS, SO, MK. Visualization: YH. Software: YH. Validation: YH. Investigation: YH. Supervision: YH. Writing-original draft: YH. Writing-review & editing: YH, EF, TM, HS, MI, RS, SO, MK. Approval of final manuscript: YH, EF, TM, HS, MI, RS, SO, MK.