Prediction of in-vitro developmental competence of early cleavage-stage mouse embryos with compact time-lapse equipment

Morphokinetic Profiling Suggests That Rapid First Cleavage Division Accurately Predicts the Chances of Blastulation in Pig In Vitro Produced Embryos

The study of pig preimplantation embryo development has several potential uses: from agriculture to the production of medically relevant genetically modified organisms and from rare breed conservation to acting as a physiologically relevant model for progressing human and other (e.g., endangered) species' in vitro fertilisation technology. Despite this, barriers to the widespread adoption of pig embryo in vitro production include lipid-laden cells that are hard to visualise, slow adoption of contemporary technologies such as the use of time-lapse incubators or artificial intelligence, poor blastulation and high polyspermy rates. Here, we employ a commercially available time-lapse incubator to provide a comprehensive overview of the morphokinetics of pig preimplantation development for the first time. We tested the hypotheses that (a) there are differences in developmental timings between blastulating and non-blastulating embryos and (b) embryo developmental morphokinetic features can be used to predict the likelihood of blastulation. The abattoir-derived oocytes fertilised by commercial extended semen produced presumptive zygotes were split into two groups: cavitating/blastulating 144 h post gamete co-incubation and those that were not. The blastulating group reached the 2-cell and morula stages significantly earlier, and the time taken to reach the 2-cell stage was identified to be a predictive marker for blastocyst formation. Reverse cleavage was also associated with poor blastulation. These data demonstrate the potential of morphokinetic analysis in automating and upscaling pig in vitro production through effective embryo selection.

Novel image analyser-assisted morphometric methodology offer unique opportunity for selection of embryos with potential for implantation

BACKGROUND

Previous studies looked into the connections between pregnancy and the Zona Pellucida (ZP) thickness and Zona Pellucida Thickness Variation (ZPTV), as well as the embryo's radius, circumference, perimeter and global symmetry. However, no research has linked embryo implantation and pregnancy to the percentage of ZP thinning, the reduction in ooplasm volume, and the increase in perivitelline space (PVS) volume. Our objective is to correlate the percentage of ZP thinning, the percentage of ooplasm volume shrinkage and the percentage of PVS increase to the implantation. These data will be used for embryo selection as well as it can be put into a software that will assist embryo selection.

MATERIALS AND METHODS

Retrospective study included 281 patients, all of them had 2 embryos transferred, 149 patients got pregnant with two gestation sacs and 132 patients did not get pregnant. All of the transferred embryos had the ZP thickness measured several times from time of ICSI till Embryo Transfer (ET), the ooplasm volume was calculated from time of ICSI till two Pronuclei (2PN) fading and the PVS was calculated from the ICSI time till the 2PN fading.

RESULTS

The first characteristic is the change in the average ZP thickness that decreased by 32.7% + 5.3% at 70 h for the implanted embryos (Group 1) versus 23.6% + 4.8% for non-implanted embryos (Group 2) p = 0.000. The second characteristic is the average reduction in the volume of the ooplasm which is 20.5% + 4.3% in Group 1 versus 15.1% + 5.2% in Group 2, p = 0.000. The third characteristic is the increase in the volume of the PVS which was 38.1% + 7.6% in Group 1 versus 31.6% + 9.7% in Group 2 p = 0.000.

CONCLUSION

The implanted embryos showed higher percent of ZP thinning, higher percent of ooplasm reduction and higher percent of PVS increase.

Are Early Embryo Cleavage Kinetics Affected by Energy Substrates in Different Culture Media?

OBJECTIVE

This study aimed to investigate the influence of different culture media on early embryonic cleavage kinetics using time-lapse analysis and to determine the possible relationships between energy substrates in culture media and the cleavage kinetics.

METHODS

A total of 10 021 embryos from 1310 couples were cultured in time-lapse incubators. Embryos cultured in Vitrolife media were allocated to group I, and those in COOK media to group II. Embryo cleavage time points up to the 8-cell stage (t2-t8) were observed after pronuclei fading.

RESULTS

The baseline demographic features, in vitro fertilization indications, ovarian stimulation protocol, oocyte-cumulus complexes, fertilization rate, together with pregnancy and perinatal outcomes were similar (P>0.05) between groups I and II. According to the time-lapse analysis, all embryos in group I showed significantly faster cleavage speed than those in group II (P<0.05). Furthermore, there was better synchrony in division (s3) and a longer length of the third cell cycle duration (cc3) in group II. Interestingly, implanted embryos in group II showed faster cleavage speed than those in group I, especially at t4 and t7. The glucose contents and multiple major amino acids were similar between the two groups. Lactic and pyruvic acid contents were generally higher in group I than those in group II.

CONCLUSION

Because different commercial culture media may influence cleavage kinetics of embryos, it is essential for embryologists to take culture media into consideration in selecting a potential embryo when using a time-lapse system before implantation.

Effects of Trichostatin A on the Timing of the First Cleavage and In Vitro Developmental Potential of Bovine Somatic Cell Nuclear Transfer Embryos

This study examined the relationship between the timing of the first cleavage and in vitro development of bovine somatic cell nuclear transfer (SCNT) embryos treated with trichostatin A (TSA). SCNT embryos were visually assessed at 22, 26, and 48 hours after activation. Each embryo with two or more distinct blastomeres was transferred into a microwell and cultured until day 7. Irrespective of TSA treatment, approximately half of the cleaved embryos were observed at 22 hours, and a significantly higher blastocyst formation rate was shown in the SCNT embryos cleaved at 22 hours than those cleaved at ≥26 hours. The blastocyst formation rate of TSA-treated embryos cleaved at 22 hours (80%) was slightly higher than that of the control embryos (70%). In addition, interferon-τ (IFN-τ) expression was significantly lower in control SCNT embryos and late-cleaving (>26 hours) TSA-treated embryos than in in vitro fertilized (IVF) embryos. However, a significant difference was not observed between TSA-treated SCNT embryos cleaved at 22 and 26 hours, and IVF embryos. These results suggest that TSA treatment has no influence on the timing of the first cleavage of SCNT embryos; however, it slightly improves the blastocyst formation rate and the expression level of IFN-τ in early-cleaving embryos.

Prospective-randomized study comparing clinical outcomes of IVF treatments where embryos were cultured individually or in a microwell group culture dish

Culturing embryos together in a microdrop of media may improve embryo quality, based on the results of animal studies, however individual identification of the embryos in such a system is not possible. The microwell group culture dish contains 9 or 16 microwells with a minimal well-to-well distance and a specific well morphology that facilitates paracrine and autocrine effects. The microwell group culture dish enables individual identification of the embryos while providing the environment that comes with similar benefits as group culture. Our aim was to investigate whether embryo culture in the microwell group culture dish (Primo Vision Dish, Vitrolife) improves IVF outcomes compared to individual culture in human IVF treatment. Five hundred thirty-two IVF-ET cycles were enrolled in this prospective randomized study in a university hospital. IVF cycles were randomized into microwell group culture and individual culture groups. Primary outcome measure was clinical pregnancy rate and secondary outcome measures were embryo quality, fertilization, implantation, delivery and embryo utilization rates. Fertilization rate in ICSI cycles was significantly higher in the microwell group culture group (70.6% vs. 64.9%, P = 0.001). Clinical pregnancy rate was 50.8% in the group culture and 40.6% in the individual culture (P = 0.022). Live birth rate was 41.5% in microwell and 32.9% in individual culture (P = 0.0496). Embryo utilization rate was higher in microwell group culture than in individual culture (80.6% vs. 75.0%; P < 0.001). Microwell group culture has a beneficial effect on IVF outcome and it also allows following up individual embryo development.ClinicalTrials.gov: NCT01774006.

The effects of temperature variation treatments on embryonic development: a mouse study

Since the development of ART, embryos have been cultured at 37 °C in an attempt to mimic the in vivo conditions and the average body temperature of an adult. However, a gradient of temperatures within the reproductive tract has been demonstrated in humans and several other mammalian species. Therefore, the aim of this study was to evaluate the effects of temperature variation treatments on mouse embryo quality through morphokinetic events, blastocyst morphology, the relative gene expression of Igf2, Bax, Bcl2 and Apaf1 and the metabolomics of individual culture media. Study groups consisted of 2 circadian treatments, T1 with embryos being cultured at 37 °C during the day and 35.5 °C during the night, T2 with 38.5 °C during the day and 37 °C during the night and a control group with constant 37 °C. Our main findings are that the lower-temperature group (T1) showed a consistent negative effect on mouse embryo development with “slow” cleaving embryos, poor-quality blastocysts, a higher expression of the apoptotic gene Apaf1, and a significantly different set of amino acids representing a more stressed metabolism. On the other hand, our higher-temperature group (T2) showed similar results to the control group, with no adverse effects on blastocyst viability.

Effects of oxygen tension and humidity on the preimplantation development of mouse embryos produced by <i>in vitro</i> fertilization: analysis using a non-humidifying incubator with time-lapse cinematography

To examine the effects of oxygen tension and humidity on early embryonic development, the preimplantation development of mouse embryos produced by in vitro fertilization was assessed by time-lapse cinematography to evaluate morphokinetic development with higher precision. Zygotes were produced from spermatozoa and oocytes from ICR mice and cultured in KSOM under low or high oxygen tension in a non-humidified incubator with time-lapse cinematography (CCM-iBIS). The developmental rates of embryos to the 4-cell and blastocyst stages under lower oxygen tension in CCM-iBIS were significantly higher than those under higher oxygen tension in CCM-iBIS. Ninety-six hours after insemination, a large number of embryos cultured under low oxygen tension developed to the hatching blastocyst stage. Embryonic development was more synchronized under lower oxygen tension. Non-humidified cultures did not affect embryonic development. On average, mouse embryos cultured at lower oxygen tension reached 2-cell at 18 h, 3-cell at 39 h, 4-cell at 40 h, initiation of compaction at 58 h, morula at 69 h, and blastocyst at 82 h after insemination. In conclusion, lower oxygen tension better supports preimplantation development of mouse embryos fertilized in vitro, and non-humidified culture conditions do not influence the embryonic development in vitro.

The Association of Kinetic Variables with Blastocyst Development and Ploidy Status

Background:

Despite a plethora of studies conducted so far, a debate is still unresolved as to whether TLM can identify predictive kinetic biomarkers or algorithms universally applicable. Therefore, this study aimed to elucidate if there is a relationship between kinetic variables and ploidy status of human embryos or blastocyst developmental potential.

Methods:

For conducting this retrospective cohort study, the normal distribution of data was verified using Kolmogorov-Smirnov test with the Lilliefors’ amendment and the Shapiro-Wilk test. Kinetic variables were expressed as median and quartiles (Q1, Q2, Q3, Q4). Mann-Whitney U-test was used to compare the median values of parameters. Univariate and multiple logistic regression models were used to assess relationship between blastocyst developmental potential or ploidy status and kinetics. Several confounding factors were also assessed.

Results:

Blastocyst developmental potential was positively correlated with the t4-t3 interval (s2) (OR=1.417, 95% CI of 1.288–1.560). s2 median value was significantly different between high- and low-quality blastocysts (0.50 and 1.33 hours post-insemination, hpi, respectively; p=0.003). In addition, timing of pronuclear appearance (tPNa) (OR=1.287; 95% CI of 1.131–1.463) had a significant relationship with ploidy changes. The median value of tPNa was statistically different (p=0.03) between euploid and aneuploid blastocysts (Euploid blastocysts=8.9 hpi; aneuploid blastocysts=10.3 hpi).

Conclusion:

The present findings are in line with the study hypothesis that kinetic analysis may reveal associations between cleavage patterns and embryo development to the blastocyst stage and ploidy status.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Back to the future: optimised microwell culture of individual human preimplantation stage embryos

Although in vitro culture of human embryos is a crucial step in assisted reproduction, the lack of focused research hampers worldwide standardisation and consistent outcomes. Only 1.2% of research papers published in five leading journals in human reproduction in 2019 focused on in vitro culture conditions, creating the impression that the optimisation process has approached its limits. On the other hand, in vitro culture of mammalian embryos is based on old principles, while there is no consensus on basic issues as density, time, medium change, gas atmosphere and small technical details including the way of drop preparation. This opinion paper aims to highlight and analyse the slow advancement in this field and stimulate research for simple and affordable solutions to meet the current requirements. A possible way for advancement is discussed in detail. Selection of embryos with the highest developmental competence requires individual culture and modification of the widely used "drop under oil" approach. Current use of three-dimensional surfaces instead of large flat bottoms is restricted to time-lapse systems, but these wells are designed for optical clarity, not for the needs of embryos. The size and shape of the original microwells (Well of the Well; WOW) offer a practical and straightforward solution to combine the benefits of communal and individual incubation and improve the overall quality of cultured embryos.

Review of computer vision application in in vitro fertilization: the application of deep learning-based computer vision technology in the world of IVF

In vitro fertilization has been regarded as a forefront solution in treating infertility for over four decades, yet its effectiveness has remained relatively low. This could be attributed to the lack of advancements for the method of observing and selecting the most viable embryos for implantation. The conventional morphological assessment of embryos exhibits inevitable drawbacks which include time- and effort-consuming, and imminent risks of bias associated with subjective assessments performed by individual embryologists. A combination of these disadvantages, undeterred by the introduction of the time-lapse incubator technology, has been considered as a prominent contributor to the less preferable success rate of IVF cycles. Nonetheless, a recent surge of AI-based solutions for tasks automation in IVF has been observed. An AI-powered assistant could improve the efficiency of performing certain tasks in addition to offering accurate algorithms that behave as baselines to minimize the subjectivity of the decision-making process. Through a comprehensive review, we have discovered multiple approaches of implementing deep learning technology, each with varying degrees of success, for constructing the automated systems in IVF which could evaluate and even annotate the developmental stages of an embryo.

Assessing equine embryo developmental competency by time-lapse image analysis

The timing of early mitotic events during preimplantation embryo development is important for subsequent embryogenesis in many mammalian species, including mouse and human, but, to date, no study has closely examined mitotic timing in equine embryos from oocytes obtained by ovum pick-up. Here, cumulus-oocyte complexes were collected by transvaginal follicular aspiration, matured invitro and fertilised via intracytoplasmic sperm injection. Each fertilised oocyte was cultured up to the blastocyst stage and monitored by time-lapse imaging for the measurement of cell cycle intervals and identification of morphological criteria indicative of developmental potential. Of the 56 fertilised oocytes, 35 initiated mitosis and 11 progressed to the blastocyst stage. Analysis of the first three mitotic divisions in embryos that formed blastocysts determined that typical blastocyst timing (median±IQR) is 30.0±17.5min, 8.8±1.7h and 0.6±1.4h respectively. Frequent cellular fragmentation, multipolar divisions and blastomere exclusion suggested that equine embryos likely contend with a high incidence of chromosomal missegregation. Indeed, chromosome-containing micronuclei and multinuclei with extensive DNA damage were observed throughout preimplantation embryogenesis. This indicates that time-lapse image analysis may be used as a non-invasive method to assess equine embryo quality in future studies.

Time-lapse imaging: the state of the art†

The introduction of time-lapse imaging to clinical in vitro fertilization practice enabled the undisturbed monitoring of embryos throughout the entire culture period. Initially, the main objective was to achieve a better embryo development. However, this technology also provided an insight into the novel concept of morphokinetics, parameters regarding embryo cell dynamics. The vast amount of data obtained defined the optimal ranges in the cell-cycle lengths at different stages of embryo development. This added valuable information to embryo assessment prior to transfer. Kinetic markers became part of embryo evaluation strategies with the potential to increase the chances of clinical success. However, none of them has been established as an international standard. The present work aims at describing new approaches into time-lapse: progress to date, challenges, and possible future directions.

LIF in embryo culture medium is a predictive marker for clinical pregnancy following IVF-ET of patients with fallopian tube obstruction

Leukemia inhibitory factor (LIF) has played a vital role in a series of reproductive events, including follicle growth, embryo growth and differentiation. However, it is unclear whether the level of LIF in embryo culture medium can be used as a marker for clinical pregnancy. In this study, we aimed to investigate whether LIF level in embryo culture medium can act as a predictive marker for pregnancy outcome of in vitro fertilization-embryo transfer (IVF-ET) in infertile women due to tubal problems. A total of 208 infertile women due to tubal problems underwent IVF-ET treatment. The women were divided into two groups according to whether they were clinically pregnant. The level of LIF in the embryo culture medium was measured, and the correlation between LIF level and embryo quality and clinical pregnancy outcome was analyzed. The embryo culture medium was collected on the day of blastocyst transplantation. Compared to non-pregnant group, LIF level in the embryo culture medium on the day of blastocyst transplantation was significantly higher in the pregnant group. LIF level in the embryo culture medium may be used as a non-invasive auxiliary biomarker for predictive clinical pregnancy in infertile women with tubal problems that using single blastocyst transfer method.

Non-invasive embryo evaluation and selection using time-lapse monitoring: Results of a randomized controlled study

OBJECTIVE

Continuous monitoring of embryos via time-lapse (TL) provides more information on embryo kinetics and morphology compared to standard daily evaluation. Embryo selection by TL could support single embryo transfer (SET). With SET multiple gestations are avoided and perinatal outcome is improved. Our primary goal was to determine whether selection of a single blastocyst based on an algorithm comprising kinetic and morphologic scores assessed through continuous TL monitoring results in superior clinical outcome compared to embryo selection based on morphology alone. A secondary goal was to assess whether a time-lapse score based on kinetic and morphologic parameters was predictive of implantation.

STUDY DESIGN

Randomized controlled trial performed in two private IVF centers in Hungary. Infertile couples scheduled to undergo 1st or 2nd IVF cycles were enrolled. Female age had to be under 36 years. The intervention was embryo evaluation/selection based on TL algorithm. Patients were randomized to SET with TL monitoring (TL-eSET) vs. SET with standard evaluation (control-eSET). Assuming an increase in pregnancy from 44% to 58%, a sample size of 202 per group was calculated based on the interim analysis at 10% information fraction. The primary outcome of the study was pregnancy rate. Secondary outcomes were miscarriage rates, live birth, perinatal outcome and the ability of a time-lapse score constructed based on kinetic and morphologic parameters to predict implantation. Chi-square tests, likelihood-ratio tests and exact tests were used for the analysis of categorical variables. Continuous variables were compared using independent group t-test and analysis of variance.

RESULTS

The study was closed after three years. Eventually 161 patients were randomized and analyzed (N = 80 TL-eSET and N = 81 control-eSET). Pregnancy rate did not significantly differ between the groups though there was a trend favoring TL selection (TL-eSET: 46.3% vs control-eSET: 34.6%, p = 0.150; OR: 1.628 (95% CI: 0.857-3.092)). The time-lapse score based on morphologic and kinetic parameters was significantly higher for blastocysts that implanted vs. those that did not (14.5 ± 1.8 vs. 12.1 ± 2.9, p = 0.0001). There were no adverse effects of the intervention.

CONCLUSIONS

Selection of a single blastocyst based on information derived from time-lapse monitoring can aid embryo selection for SET.

Embryo culture conditions are significantly improved during uninterrupted incubation: A randomized controlled trial

A parallel group superiority prospective randomised controlled trial was devised to compare the culture characteristics of human pre-implantation stage embryos during uninterrupted culture in a time lapse incubator (TLI) versus the conventional model of interrupted culture in a standard incubator (SI) under low oxygen tension using a single step medium. 221 patients aged 35-and-under, 124 patients aged between 36 and 39 and 86 patients aged 40-and-over years were randomised and cultured either in a SI or in a TLI. Patients in the three age groups were distributed between the TLI and SI in a 1:1 ratio. The development of embryos on days 2, 3 and 5, and the clinical pregnancy and implantation rates were recorded. The fertilisation rate, development of day 2 and clinical pregnancy rates were similar in both treatments but the 8-cell development rate in all age groups combined (p = 0.016), blastocyst development rate (p = 0.0022) and the implantation rate (p = 0.0022) was significantly higher for the uninterrupted culture. These findings demonstrated significant differences between the two incubation groups. It also indicated less efficacious embryonic development with age in both treatments which appeared more pronounced in the conventional incubator. In conclusion uninterrupted culture is superior compared to the interrupted incubation culture system.

Comparison of the development of human embryos cultured in either an EmbryoScope or benchtop incubator

PURPOSE

In this current study, our main goal was to establish that EmbryoScope incubation environment is comparable to standard incubation.

METHODS

The development of sibling human zygotes was compared after culture in either a benchtop incubator (SI) or an EmbryoScope time-lapse incubator (ES). Between May 2015 to April 2016, a total of 581 normally fertilized 2PN, pronuclear-stage embryos, from 47 patients were allocated to culture in either a benchtop incubator (SI) or an EmbryoScope incubator (ES).

RESULTS

The development of embryos to cleavage (up to day 3) and blastocyst stages (day 5/6) was compared between the two different incubators. The proportion of good quality embryos was higher in the ES group compared to the SI on day 2 (66.8 vs. 50.5%, P = 0.014) and on day 3 (75.1 vs. 56.0%, P = 0.006). Those differences were statistically significant. A higher proportion of embryos developed to good quality blastocysts when cultured in the EmbryoScope compared to the benchtop (49.4 vs. 42.0%, P = 0.24), but this was not significant. Finally, no significant differences were noted with the proportion of blastocysts chosen for cryopreservation on day 5/6 in the two incubators.

CONCLUSIONS

The findings support the view that the EmbryoScope incubator supports at least equivalent in vitro development of human embryos compared to other standard incubation methods and may promote improved development during early cleavage stages.

Embryo density may affect embryo quality during in vitro culture in a microwell group culture dish

PURPOSE

Culturing embryos in groups is a common practice in mammalian embryology. Since the introduction of different microwell dishes, it is possible to identify oocytes or embryos individually. As embryo density (embryo-to-volume ratio) may affect the development and viability of the embryos, the purpose of this study was to assess the effect of different embryo densities on embryo quality.

METHODS

Data of 1337 embryos from 228 in vitro fertilization treatment cycles were retrospectively analyzed. Embryos were cultured in a 25 μl microdrop in a microwell group culture dish containing 9 microwells. Three density groups were defined: Group 1 with 2-4 (6.3-12.5 μl/embryo), Group 2 with 5-6 (4.2-5.0 μl/embryo), and Group 3 with 7-9 (2.8-3.6 μl/embryo) embryos.

RESULTS

Proportion of good quality embryos was higher in Group 2 on both days (D2: 18.9 vs. 31.5 vs. 24.7%; p < 0.001; D3: 19.7 vs. 27.1 vs. 21.2%; p = 0.029; Group 1. vs. Group 2. vs. Group 3). Cell number on Day 3 differed between Groups 1 and 2 (6.8 ± 2.2; 7.3 ± 2.1; p = 0.004) and Groups 2 and 3 (7.3 ± 2.1 vs. 7.0 ± 2.0; p = 0.014).

CONCLUSIONS

Culturing 5-6 embryos together in a culture volume of 25 μl may benefit embryo quality. As low egg number, position, and distance of the embryos may influence embryo quality, results should be interpreted with caution.

In vitro culture of individual mouse preimplantation embryos: the role of embryo density, microwells, oxygen, timing and conditioned media

Single embryo culture is suboptimal compared with group culture, but necessary for embryo monitoring, and culture systems should be improved for single embryos. Pronucleate mouse embryos were used to assess the effect of culture conditions on single embryo development. Single culture either before or after compaction reduced cell numbers (112.2 ± 3.1; 110.2 ± 3.5) compared with group culture throughout (127.0 ± 3.4; P < 0.05). Reduction of media volume from 20 µl to 2 µl increased blastocyst cell numbers in single embryos cultured in 5% oxygen (84.4 ± 3.2 versus 97.8 ± 2.8; P < 0.05), but not in 20% oxygen (55.2 ± 2.9 versus 57.1 ± 2.8). Culture in microwell plates for the EmbryoScope and Primo Vision time-lapse systems changed cleavage timings and increased inner cell mass cell number (24.1 ± 1.0; 23.4 ± 1.2) compared with a 2 µl microdrop (18.4 ± 1.0; P < 0.05). Addition of embryo-conditioned media to single embryos increased hatching rate and blastocyst cell number (91.5 ± 4.7 versus 113.1 ± 4.4; P < 0.01). Single culture before or after compaction is therefore detrimental; oxygen, media volume and microwells influence single embryo development; and embryo-conditioned media may substitute for group culture.

Vertebrate Embryonic Cleavage Pattern Determination

The pattern of the earliest cell divisions in a vertebrate embryo lays the groundwork for later developmental events such as gastrulation, organogenesis, and overall body plan establishment. Understanding these early cleavage patterns and the mechanisms that create them is thus crucial for the study of vertebrate development. This chapter describes the early cleavage stages for species representing ray-finned fish, amphibians, birds, reptiles, mammals, and proto-vertebrate ascidians and summarizes current understanding of the mechanisms that govern these patterns. The nearly universal influence of cell shape on orientation and positioning of spindles and cleavage furrows and the mechanisms that mediate this influence are discussed. We discuss in particular models of aster and spindle centering and orientation in large embryonic blastomeres that rely on asymmetric internal pulling forces generated by the cleavage furrow for the previous cell cycle. Also explored are mechanisms that integrate cell division given the limited supply of cellular building blocks in the egg and several-fold changes of cell size during early development, as well as cytoskeletal specializations specific to early blastomeres including processes leading to blastomere cohesion. Finally, we discuss evolutionary conclusions beginning to emerge from the contemporary analysis of the phylogenetic distributions of cleavage patterns. In sum, this chapter seeks to summarize our current understanding of vertebrate early embryonic cleavage patterns and their control and evolution.

Prediction of blastocyst development and implantation potential in utero based on the third cleavage and compaction times in mouse pre-implantation embryos

Cytokinesis and cell division during pre-implantation embryonic development occur as an orchestrated spatiotemporal program. Cleavage, compaction, and blastulation in pre-implantation embryos are essential for successful implantation and pregnancy. Their alteration is associated with chromosomal imbalance and loss of developmental competence. In this study, we evaluated the time of cleavage and compaction as predictors for in vitro pre- and peri-implantation development and in utero implantation potential by time-lapse monitoring. Mouse 2-cell embryos were collected on 1.5 days post coitum (dpc) and were individually cultured to the outgrowth (OG) stage (7.5 dpc). Developmental stages were classified as 3-cell, 4-cell, 8-cell, morula, blastocyst, and OG. Cut-off times for successful blastocyst development were determined by receiver operating characteristic curve analysis. When cut-off times were set as 9 h for the third cleavage from the 2- to 4-cell stage, and 40 h for compaction from the 2-cell to morula stage, blastocyst and OG development rates, respectively, were significantly higher (P < 0.0001). Embryos were grouped according to the above cut-off time and transferred to the contralateral uterine horn on 3.5 dpc. Implantation rates in utero on 5.5 dpc were significantly higher in early third cleaved (≤ 9 h from 2- to 4-cell) and early compacted embryos (≤ 40 h from 2-cell to morula) than those in delayed embryos (P < 0.05). Therefore, the time of the third cleavage from 2- to the 4-cell stage and compaction from 2-cell to morula stage may be a useful morphokinetic parameter for predicting developmental potential, including successful implantation and pregnancy in human in vitro fertilization-embryo transfer programs.

Amino Acid Metabolism in Human Embryos

The aim of this study was to find some relationship between amino acid metabolism and the embryo morphokinetic parameters studied via time-lapse analysis. Study included 48 human embryo samples and their culture media. Two groups of embryos were identified: embryos reached the 8-cell stage on day 3 (n=34) and embryos failed to develop at any point during the incubation (n=14). Amino acids levels were measured on day 3 of embryo development; using time-lapse analysis, the precise timing of embryo cleavage, synchrony of division, grade of fragmentation etc. were established. No statistically significant differences between dividing and arresting embryos were observed in terms of amino acids production/consumption and turnover. Amino acids which were part of the culture medium did not exhibit any statistically significant correlation with kinetic parameters with the exception of the grade of fragmentation on day 3; there were negative correlation with glutamate, and positive with glutamine, glycine and taurine. In some dividing and in some arresting embryos appeared new amino acids which strongly correlated with each other, with methionine, but not with any other amino acid that is a regular part of the culture medium.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

Observation of human embryonic behavior in vitro by high-resolution time-lapse cinematography

Assisted reproductive technology (ART) has yielded vast amounts of information and knowledge on human embryonic development in vitro; however, still images provide limited data on dynamic changes in the developing embryos. Using our high-resolution time-lapse cinematography (hR-TLC) system, we were able to describe normal human embryonic development continuously from the fertilization process to the hatched blastocyst stage in detail. Our hR-TLC observation also showed the embryonic abnormality of a third polar body (PB)-like substance likely containing a small pronucleus being extruded and resulting in single-pronucleus (1PN) formation, while our molecular biological investigations suggested the possibility that some 1PN embryos could be diploid, carrying both maternal and paternal genomes. Furthermore, in some embryos the extruded third PB-like substance was eventually re-absorbed into the ooplasm resulting in the formation of an uneven-sized, two-PN zygote. In addition, other hR-TLC observations showed that cytokinetic failure was correlated with equal-sized, multi-nucleated blastomeres that were also observed in the embryo showing early initiation of compaction. Assessment combining our hR-TLC with molecular biological techniques enables a better understanding of embryonic development and potential improvements in ART outcomes.

Morphokinetic Evaluation of Embryo Development in a Mouse Model: Functional and Molecular Correlates

Although time-lapse analysis of early embryo cleavage parameters (morphokinetics) predicts blastocyst development, it has not been definitively linked to establishing pregnancy and live birth. For example, a direct comparison of the developmental potential of embryos with optimal kinetic parameters compared to suboptimal kinetics has not been performed with human embryos. To ascertain whether such a linkage exists, we developed a mouse model of morphokinetic analysis of early embryo cleavage using time-lapse microscopy to predict blastocyst formation and tested whether cleavage parameters predict pregnancy outcome by transferring morphokinetically optimal and suboptimal embryos into a single host. Using classification and regression trees, we established that the timing of the second and third mitotic divisions (division from two to three and three to four cells, respectively) predicts blastocyst development in the mouse. Using this prediction model, we found that the incidence of sustained implantation at mid-gestation was significantly higher for the optimal compared to suboptimal embryos. In addition, the incidence of resorption among implanted embryos was significantly higher in the suboptimal compared to the optimal group. Transcript profiling of optimal and suboptimal embryos revealed minimal differences between the two groups, suggesting that time-lapse imaging of early embryo cleavage events provides additional information regarding developmental competence apart from gene expression.

Chromosomal instability in mammalian pre-implantation embryos: potential causes, detection methods, and clinical consequences

Formation of a totipotent blastocyst capable of implantation is one of the first major milestones in early mammalian embryogenesis, but less than half of in vitro fertilized embryos from most mammals will progress to this stage of development. Whole chromosomal abnormalities, or aneuploidy, are key determinants of whether human embryos will arrest or reach the blastocyst stage. Depending on the type of chromosomal abnormality, however, certain embryos still form blastocysts and may be morphologically indistinguishable from chromosomally normal embryos. Despite the implementation of pre-implantation genetic screening and other advanced in vitro fertilization (IVF) techniques, the identification of aneuploid embryos remains complicated by high rates of mosaicism, atypical cell division, cellular fragmentation, sub-chromosomal instability, and micro-/multi-nucleation. Moreover, several of these processes occur in vivo following natural human conception, suggesting that they are not simply a consequence of culture conditions. Recent technological achievements in genetic, epigenetic, chromosomal, and non-invasive imaging have provided additional embryo assessment approaches, particularly at the single-cell level, and clinical trials investigating their efficacy are continuing to emerge. In this review, we summarize the potential mechanisms by which aneuploidy may arise, the various detection methods, and the technical advances (such as time-lapse imaging, "-omic" profiling, and next-generation sequencing) that have assisted in obtaining this data. We also discuss the possibility of aneuploidy resolution in embryos via various corrective mechanisms, including multi-polar divisions, fragment resorption, endoreduplication, and blastomere exclusion, and conclude by examining the potential implications of these findings for IVF success and human fecundity.

Morphokinetics of cloned mouse embryos treated with epigenetic drugs and blastocyst prediction

Time-lapse monitoring of somatic cell nuclear transfer (SCNT) embryos may help to predict developmental success and increase birth and embryonic stem cells (ESC) derivation rates. Here, the development of ICSI fertilized embryos and of SCNT embryos, non-treated or treated with either psammaplin A (PsA) or vitamin C (VitC), was monitored, and the ESC derivation rates from the resulting blastocysts were determined. Blastocyst rates were similar among PsA-treated and VitC-treated SCNT embryos and ICSI embryos, but lower for non-treated SCNT embryos. ESC derivation rates were higher in treated SCNT embryos than in non-treated or ICSI embryos. Time-lapse microscopy analysis showed that non-treated SCNT embryos had a delayed development from the second division until compaction, lower number of blastomeres at compaction and longer compaction and cavitation durations compared with ICSI ones. Treatment of SCNT embryos with PsA further increased this delay whereas treatment with VitC slightly reduced it, suggesting that both treatments act through different mechanisms, not necessarily related to their epigenetic effects. Despite these differences, the time of completion of the third division, alone or combined with the duration of compaction and/or the presence of fragmentation, had a strong predictive value for blastocyst formation in all groups. In contrast, we failed to predict ESC derivation success from embryo morphokinetics. Time-lapse technology allows the selection of SCNT embryos with higher developmental potential and could help to increase cloning outcomes. Nonetheless, further studies are needed to find reliable markers for full-term development and ESC derivation success.

Mammalian pre-implantation chromosomal instability: species comparison, evolutionary considerations, and pathological correlations

Pre-implantation embryo development in mammals begins at fertilization with the migration and fusion of the maternal and paternal pro-nuclei, followed by the degradation of inherited factors involved in germ cell specification and the activation of embryonic genes required for subsequent cell divisions, compaction, and blastulation. The majority of studies on early embryogenesis have been conducted in the mouse or non-mammalian species, often requiring extrapolation of the findings to human development. Given both conserved similarities and species-specific differences, however, even comparison between closely related mammalian species may be challenging as certain aspects, including susceptibility to chromosomal aberrations, varies considerably across mammals. Moreover, most human embryo studies are limited to patient samples obtained from in vitro fertilization (IVF) clinics and donated for research, which are generally of poorer quality and produced with germ cells that may be sub-optimal. Recent technical advances in genetic, epigenetic, chromosomal, and time-lapse imaging analyses of high quality whole human embryos have greatly improved our understanding of early human embryogenesis, particularly at the single embryo and cell level. This review summarizes the major characteristics of mammalian pre-implantation development from a chromosomal perspective, in addition to discussing the technological achievements that have recently been developed to obtain this data. We also discuss potential translation to clinical applications in reproductive medicine and conclude by examining the broader implications of these findings for the evolution of mammalian species and cancer pathology in somatic cells.

Relationship between pregnancy, embryo development, and sperm deoxyribonucleic acid fragmentation dynamics

The way the dynamics of DNA fragmentation affects the growth of embryos in real time, and effectiveness of infertility treatment using the ICSI procedure were determined in 148 couples treated with the ICSI technique. The percentage of sperm with fragmented DNA (known as the DNA fragmentation index [DFI]) in semen samples was determined at 3, 6 and 12 h. Embryo culture was assessed continuously during 12 h of observation monitoring.

Statistically significant difference was found in DFI at 12 h and outcome of treatment. For the remaining time intervals, no statistically significant differences were noted. An analysis of relationship between the DFI dynamics over time at individual measurements and achievement of pregnancy, confirmed a statistically significant relationship between the rate measured at 6–12 h of observations of DFI changes (DFI 12 h%/h), and achieving pregnancy. Correlation was observed between DFI (during 0, 3, 6 and 12 h), the growth rate in DFI, and time of embryo development. A statistically significant relationship was found between the rate from the start to the end of observations of the DFI, and outcome of treatment.

Intensity level regarding fragmentation of sperm DNA and its growth rate affected the time of embryo development in the ICSI procedure. The most significant prognostic factor for achieving pregnancy was intensification of sperm DNA fragmentation after 12 h.

Comparison of different fertilisation media for an in vitro maturation?fertilisation?culture system using flow-cytometrically sorted X chromosome-bearing spermatozoa for bovine embryo production

High demand exists among commercial cattle producers for in vitro-derived bovine embryos fertilised with female sex-sorted spermatozoa from high-value breeding stock. The aim of this study was to evaluate three fertilisation media, namely M199, synthetic oviductal fluid (SOF) and Tyrode's albumin-lactate-pyruvate (TALP), on IVF performance using female sex-sorted spermatozoa. In all, 1143, 1220 and 1041 cumulus-oocyte complexes were fertilised in M199, SOF and TALP, respectively. There were significant differences among fertilisation media (P < 0.05) in cleavage rate (M199 = 57%, SOF = 71% and TALP = 72%), blastocyst formation (M199 = 9%, SOF = 20% and TALP = 19%), proportion of Grade 1 blastocysts (M199 = 15%, SOF = 52% and TALP = 51%), proportion of Grade 3 blastocysts (M199 = 58%, SOF = 21% and TALP = 20%) and hatching rates (M199 = 29%, SOF = 60% and TALP = 65%). The inner cell mass (ICM) and trophectoderm (TE) cells of Day 7 blastocysts were also affected by the fertilisation medium. Embryos derived from SOF and TALP fertilisation media had higher numbers of ICM, TE and total cells than those fertilised in M199. In conclusion, fertilisation media affected cleavage rate, as well as subsequent embryo development, quality and hatching ability. SOF and TALP fertilisation media produced significantly more embryos of higher quality than M199.

The effect of sperm DNA fragmentation on the dynamics of the embryonic development in intracytoplasmatic sperm injection

The genetic integrity of sperm DNA can contribute to the infertility problems experienced by couples. Sperm DNA fragmentation (SDF) is the most common DNA abnormality in male gametes, and yet its effect on embryo kinetics has not been widely studied. Embryo morphokinetic parameters during the first days of embryo culture after intracytoplasmatic sperm injection (ICSI) are weakly predictive of both embryo development and pregnancy outcome. This study investigated the effect of SDF on embryo morphokinetic parameters following ICSI. The DNA fragmentation index (DFI) in spermatozoa from all males in the study (n = 165) was determined before ICSI and the morphokinetic parameters of the embryos (n = 165) were monitored via time-lapse recording. We found that a low DFI index in spermatozoa corresponded with embryos that reached the blastocyst stage at a faster rate after ICSI. Overall, lower SDF levels were also found in the group of patients that achieved pregnancy. Thus, higher SDF levels can slow down embryo morphokinetic parameters, and may be predictive of pregnancy outcomes after ICSI.

Why we should not select the faster embryo: lessons from mice and cattle

Many studies have shown that in vitro culture can negatively impact preimplantation development. This necessitates some selection criteria for identifying the best-suited embryos for transfer. That said, embryo selection after in vitro culture remains a subjective process in most mammalian species, including cows, mice and humans. General consensus in the field is that embryos that develop in a timely manner have the highest developmental competence and viability after transfer. Herein lies the key question: what is a timely manner? With emerging data in bovine and mouse supporting increased developmental competency in embryos with moderate rates of development, it is time to question whether the fastest developing embryos are the best embryos for transfer in the human clinic. This is especially relevant to epigenetic gene regulation, including genomic imprinting, where faster developing embryos exhibit loss of imprinted methylation, as well as to sex selection bias, where faster developmental rates of male embryos may lead to biased embryo transfer and, in turn, biased sex ratios. In this review, we explore evidence surrounding the question of developmental timing as it relates to bovine embryo quality, mouse embryo quality and genomic imprint maintenance, and embryo sex.

Embryo selection: the role of time-lapse monitoring

In vitro fertilization has been available for over 3 decades. Its use is becoming more widespread worldwide, and in the developed world, up to 5% of children have been born following IVF. It is estimated that over 5 million children have been conceived in vitro. In addition to giving hope to infertile couples to have their own family, in vitro fertilization has also introduced risks as well. The risk of multiple gestation and the associated maternal and neonatal morbidity/mortality has increased significantly over the past few decades. While stricter transfer policies have eliminated the majority of the high-order multiples, these changes have not yet had much of an impact on the incidence of twins. A twin pregnancy can be avoided by the transfer of a single embryo only. However, the traditionally used method of morphologic embryo selection is not predictive enough to allow routine single embryo transfer; therefore, new screening tools are needed. Time-lapse embryo monitoring allows continuous, non-invasive embryo observation without the need to remove the embryo from optimal culturing conditions. The extra information on the cleavage pattern, morphologic changes and embryo development dynamics could help us identify embryos with a higher implantation potential. These technologic improvements enable us to objectively select the embryo(s) for transfer based on certain algorithms. In the past 5-6 years, numerous studies have been published that confirmed the safety of time-lapse technology. In addition, various markers have already been identified that are associated with the minimal likelihood of implantation and others that are predictive of blastocyst development, implantation potential, genetic health and pregnancy. Various groups have proposed different algorithms for embryo selection based on mostly retrospective data analysis. However, large prospective trials are needed to study the full benefit of these (and potentially new) algorithms before their introduction into daily practice can be recommended.

Preimplantation genetic screening (PGS) with Comparative genomic hybridization (CGH) following day 3 single cell blastomere biopsy markedly improves IVF outcomes while lowering multiple pregnancies and miscarriages

PURPOSE

To determine benefits of cleavage-stage preimplantation genetic screening (PGS) by array comparative genomic hybridization (CGH).

METHODS

A retrospective case-control study was performed at a tertiary care university-affiliated medical center. Implantation rate was looked at as a primary outcome. Secondary outcomes included clinical and ongoing pregnancy rates, as well as multiple pregnancy and miscarriage rates. Thirty five patients underwent 39 fresh cycles with PGS by aCGH and 311 similar patients underwent 394 invitro fertilization cycles.

RESULT(S)

The implantation rate in the CGH group doubled when compared to the control group (52.63 % vs. 19.15 %, p = < 0.001), clinical pregnancy rate was higher (69.23 % vs. 43.91 %, p = 0.0002), ongoing pregnancy rate almost doubled (61.54 % vs. 32.49 %, p = < 0.0001), multiple pregnancy rate decreased (8.33 % vs. 34.38 %, p = 0.0082) and miscarriage rate trended lower (11.11 % vs. 26.01 %, p = 0.13).

CONCLUSION

Cleavage stage PGS with CGH is a feasible and safe option for aneuploidy screening that shows excellent outcomes when used in fresh cycles. This is the first report of cleavage stage PGS by CGH showing improved ongoing pregnancy rates.

New approaches to embryo selection

Embryo selection has been an important topic since the introduction of assisted reproduction, with embryo morphology being the most obvious criterion. Although morphology serves as indicator for overall IVF laboratory quality, its statistical assessment limits the possibility to identify the most implantation-competent embryos. In order to reach a direct picture of the developing embryo, invasive procedures such as preimplantation genetic screening or transcriptome and proteome analysis of biopsied embryonic tissue were initially prioritized and are still under investigation. More recently, focus has shifted towards noninvasive techniques that maintain the integrity of the embryo. Metabolomic profiling of culture medium from growing embryos attracted much research. Although successful in a pilot study, that approach failed in a randomized controlled trial. Other metabolomics studies are on their way but not yet available for routine clinical use. The most promising strategy at present is the combined evaluation of morphology and developmental kinetics using time-lapse imaging. This has brought new insights into certain characteristics that enable deselection of embryos at an early stage of development and to identify others with high potential for successful implantation. However, there is still considerable room for improvement. Further strategies will most likely involve the combination of several different approaches.

Advances in quality control: mouse embryo morphokinetics are sensitive markers of in vitro stress

STUDY QUESTION

Can time-lapse analysis of cell division timings [morphokinetics (MK)] in mouse embryos detect toxins at concentrations that do not affect blastocyst formation?

SUMMARY ANSWER

An MK algorithm enhances assay sensitivity while providing results 24–48 h sooner than the traditional mouse embryo assay (MEA).

WHAT IS KNOWN ALREADY

Current quality control testing methodology is sensitive but further improvements are needed to assure optimal culture conditions. MKs of embryo development may detect small variations in culture conditions.

STUDY DESIGN

Cross sectional—control versus treatment. Mouse embryo development kinetics of 466 embryos were analyzed according to exposure to various concentrations of toxins and toxic mineral oil.

MATERIALS, SETTING, METHODS

Cryopreserved 1-cell embryos from F1 hybrid mice were cultured with cumene hydroperoxide (CH) (0, 2, 4, 6 and 8 µM) and Triton X-100 (TX-100; 0, 0.0008, 0.0012, 0.0016 and 0.002%). Using the Embryoscope, time-lapse images were obtained every 20 min for 120 h in seven focal planes. End-points were timing and pattern of cell division and embryo development. The blastocyst rate (BR) was defined as the percentage of embryos that developed to the expanded blastocyst stage within 96 h.

MAIN RESULTS AND THE ROLE OF CHANCE

BR was not affected for embryos cultured in the three lowest concentrations of CH and the four lowest concentrations of TX-100. In contrast, a unique MK model detected all concentrations tested (P < 0.05). The MK model identified toxicity in two lots of toxic mineral oil that did not affect BR (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

A limited number of toxins were used so that the results may not apply to all potential embryo toxins. A larger sample size may also demonstrate other statistically significant developmental kinetic parameters.

WIDER IMPLICATIONS OF THE FINDINGS

MKs in mouse embryos are a sensitive and efficient method for quality control testing of in vitro culture conditions. BR, the end-point of traditional quality control assays, did not detect sublethal concentrations of toxins in the culture milieu in our study. This study demonstrates that temporal variation at key developmental stages reflects the quality of the culture environment. An MEA that incorporates MK will provide enhanced sensitivity and faster turn-around times.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by Mayo Clinic Department of Obstetrics and Gynecology Small Grant Program. The authors have no competing interests to declare.

The use of morphokinetic parameters to select all embryos with full capacity to implant

PURPOSE

Embryo kinetics analysis is an emerging tool for selecting embryo(s) for transfer. The aim of the present study was to determine morphokinetic parameters easily usable in the laboratory and predictive of embryo development and, most importantly, of embryo competence in producing a clinical pregnancy after day 5 transfer.

METHODS

A retrospective time-lapse monitoring analysis of morphokinetic parameters for 72 fully implanted embryos (group A) were compared to 106 non-implanted embryos (group B), and to 66 embryos with arrested development from the same pool of group A. All the embryos were from 78 patients undergoing ICSI treatment and day 5 embryo transfers.

RESULTS

A day 3 embryo will develop into a viable blastocyst if the following ranges of morphokinetic parameters are met: t1 (between 18.4 h and 30.9 h post-ICSI), t2 (21.4-34.8 h), t4 (33.1-57.2 h), t7 (46.1-82.5 h), t8 (46.4-97.8 h), tC-tF (7.7-22.9 h) and s3 (0.7-30.8 h). On day 5 embryos with the highest probability to implant are those with a cc3 between 9.7 h and 21 h.

CONCLUSIONS

Morphokinetic parameters are helpful to make appropriate decisions for the disposition of each embryo. It is recommended that each laboratory should determine its own ranges of in vitro development (IVD-MKP) and implantation-associated (IMP-MKP) morphokinetic parameters.