Alleviation of the '2-cell block' and development to the blastocyst of CF1 mouse embryos: role of amino acids, EDTA and physical parameters

The Istanbul consensus update: a revised ESHRE/ALPHA consensus on oocyte and embryo static and dynamic morphological assessment†,‡

STUDY QUESTION

What are the current recommended criteria for morphological assessment of oocytes, zygotes, and embryos?

SUMMARY ANSWER

The present ESHRE/Alpha Scientists in Reproductive Medicine consensus document provides several novel recommendations to assess oocyte and embryo morphology and rank embryos for transfer.

WHAT IS KNOWN ALREADY

A previous Alpha Scientists in Reproductive Medicine/ESHRE consensus on oocyte and embryo morphological assessment was published in 2011. After more than a decade, and the integration of time-lapse technology into embryo culture and assessment, a thorough review and update was needed.

STUDY DESIGN, SIZE, DURATION

A working group consisting of Alpha Scientists in Reproductive Medicine executive committee members and ESHRE Special interest group of Embryology members formulated recommendations on oocyte and embryo assessment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The working group included 17 internationally recognized experts with extensive experience in clinical embryology. Seven members represented Alpha Scientists in Reproductive Medicine and eight members represented ESHRE, along with to two methodological experts from the ESHRE central office. Based on a systematic literature search and discussion of existing evidence, the recommendations of the Istanbul Consensus (2011) were reassessed and, where appropriate, updated based on consensus within the working group. A stakeholder review was organized after the updated draft was finalized. The final version was approved by the working group, the Alpha executive committee and the ESHRE Executive Committee.

MAIN RESULTS AND THE ROLE OF CHANCE

This updated consensus paper provides 20 recommendations focused on the timeline of preimplantation developmental events and morphological criteria for oocyte, zygote, and embryo assessment. Based on duration of embryo culture, recommendations are given on the frequency and timing of assessments to ensure consistency and effectiveness.

LIMITATIONS, REASONS FOR CAUTION

Several criteria relevant to oocyte and embryo morphology have not been well studied, leading to either a recommendation against their use for grading or for their use in ranking rather than grading. Future updates may require further revision of these recommendations.

WIDER IMPLICATIONS OF THE FINDINGS

This document provides embryologists with advice on best practices when assessing oocyte and embryo quality based on the most recent evidence.

STUDY FUNDING/COMPETING INTEREST(S)

The consensus meeting and writing of the paper were supported by funds from ESHRE and Alpha Scientists in Reproductive Medicine. The working group members did not receive any payment. G.C. declared payments or honoraria for lectures from Gedeon Richter and Cooper Surgical. A.C. declared text book royalties (Mastering Clinical Embryology, published 2024), consulting fees from Cooper Surgical, Gedeon Richter and TMRW Life Sciences, honoraria for lectures from Merck, Ferring, and Gedeon Richter, and participation in the HFEA Scientific Advances Committee; she also disclosed being treasurer and vice-president of Alpha Scientists in Reproductive Medicine, a shareholder in Care Fertility Limited and Fertile Mind Limited, and having stock options in TMRW Life Sciences and U-Ploid Biotechnology Ltd. L.R. declared consulting fees from Organon, payments or honoraria for lectures from Merck, Organon, IBSA, Finox, Geden Richter, Origio, Organon, Ferring, Fundation IVI; she also disclosed being a member of the Advisory Scientific Board of IVIRMA (Paid) and a member of the Advisory Scientific Board of Nterilizer (unpaid). I.S. declared payments or honoraria for lectures from Vitrolife and Cooper Surgical, and stock options from Alife Health. M.A. declared payments or honoraria for lectures from Vitrolife and support for attending meetings from Vitrolife and Cooper Surgical (both unrelated to this manuscript). The other authors have no conflicts of interest to declare.

DISCLAIMER

This Good Practice Recommendations (GPRs) document represents the consensus views of the members of this working group based on the scientific evidence available at the time of the meeting. GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care or be exclusive of other methods of care reasonably directed to obtaining the same results. They do not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type.

Zinc eluted from glassware is a risk factor for embryo development in human and animal assisted reproduction†

In assisted reproduction, many factors in the culture environment, including light, temperature, pH, and culture media, can reduce preimplantation embryo viability. Laboratory glassware is also a known risk factor for in vitro embryos; however, the underlying mechanisms that disrupt embryonic development remain unclear. We identified Zn eluted from glassware as an embryotoxic substance. In mouse embryos, Zn induced delayed development, abnormalities in chromosome segregation, cytokinesis, zygotic gene activation (e.g. Zscan4a and murine endogenous retrovirus with leucine, also known as MERVL), and aberrantly upregulated developmental gene expression (e.g. Hoxa1, Hoxb9, T, and Fgf8) that could be mediated through metal regulatory transcription factors (e.g. Mtf1). Subsequently, Zn exposure led to significantly reduced blastocyst formation. Post-implantation, Zn-exposed embryos were associated with normal birth rates, however, the birth weight increased by an average of 18% compared with embryos cultured without Zn. Furthermore, Zn exposure affected the development of bovine and human embryos, with species-based variation in the strength and timing of these effects. To mitigate these embryotoxic effects, we identified a method to prevent glass toxicity using chelating agents. This research not only highlights the importance of risk control in embryo culture but also facilitates the development of safe and effective methods for assisted reproduction.

The composition of commercially available human embryo culture media

STUDY QUESTION

What is the composition of currently available commercial human embryo culture media provided by seven suppliers, for each stage of human preimplantation embryo development?

SUMMARY ANSWER

While common trends existed across brands, distinct differences in composition underlined the absence of a clear standard for human embryo culture medium formulation.

WHAT IS KNOWN ALREADY

The reluctance of manufacturers to fully disclose the composition of their human embryo culture media generates uncertainty regarding the culture conditions that are used for human preimplantation embryo culture. The critical role of the embryo culture environment is well-recognized, with proven effects on IVF success rates and child outcomes, such as birth weight. The lack of comprehensive composition details restricts research efforts crucial for enhancing our understanding of its impacts on these outcomes. The ongoing demand for greater transparency remains unmet, highlighting a significant barrier in embryo culture medium optimization.

STUDY DESIGN, SIZE, DURATION

For this study, 47 different human embryo culture media and protein supplements were purchased between December 2019 and June 2020; they comprise complete media (n = 23), unsupplemented media (n = 14), and supplements (n = 10). Unsupplemented media were supplemented with each available supplement from the same brand (n = 33 combinations). All samples were directly frozen in liquid nitrogen and stored at -80°C until composition analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We determined the concentrations of 40 components in all samples collected (n = 80). Seven electrolytes (calcium, chloride, iron, magnesium, phosphate, potassium, sodium), glucose, immunoglobulins A, G, and M (IgA, IgG, IgM), uric acid, alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), and albumin, as well as the total protein concentration, were determined in each sample using a Cobas 8000 Analyser (Roche Diagnostics). Analysis of pyruvate, lactate, carnitine, and 21 amino acids was achieved with Ultra-High Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS/MS).

MAIN RESULTS AND THE ROLE OF CHANCE

Our analysis showed that generally, the concentrations of components of ready-to-use human embryo culture media align with established assumptions about the changing needs of an embryo during early development. For instance, glucose concentrations displayed a high-low-high pattern in sequential media systems from all brands: 2.5-3 mM in most fertilization media, 0.5 mM or below in all cleavage stage media, and 2.5-3.3 mM in most blastocyst stage media. Continuous media generally resembled glucose concentrations of cleavage stage media. However, for other components, such as lactate, glycine, and potassium, we observed clear differences in medium composition across different brands. No two embryo culture media compositions were the same. Remarkably, even embryo culture media from brands that belong to the same parent company differed in composition. Additionally, the scientific backing for the specific concentrations used and the differences in the composition of sequential media is quite limited and often based on minimal in vivo studies of limited sample size or studies using animal models.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

We used a targeted approach and performed a selection of tests which limit the composition analysis to this set of analytes.

WIDER IMPLICATIONS OF THE FINDINGS

Comprehensive disclosure and complete transparency concerning the composition of human embryo culture media, including the exact concentration of each component, are crucial for evidence-based improvements of culture media for human preimplantation embryos.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by ZonMw (https://www.zonmw.nl/en), Programme Translational Research 2 (project number 446002003). M.G. declares an unrestricted research grant from Ferring not related to the presented work, paid to the institution VU Medical Center. The remaining authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Comparison of Preimplantation Mouse Embryos with Different Genetic Backgrounds as Models for Evaluating Human Embryo Culture Media Composition

Can the best culture medium be determined by mouse embryo testing? Zygotes/embryos of four different mouse strains: inbred Balb/c (n = 79) and C57Bl/6 (n = 95), F1 hybrid DBA/2*C57Bl/6 (n = 133), and outbred ICR (n = 69) were incubated in vitro in four culture media: 1-Step Culture Medium (VitaVitro), CSC medium (Irvine Scientific), Sage 1-Step medium (Origio), G-TL medium (Vitrolife). The embryos were cultured under standard conditions at atmospheric oxygen: 37℃; 6% CO2, 100% humidity. Standard MEA-test parameters (number of expanded blastocysts on E4.5), as well as additional characteristics (embryo development on E2.5-E4.5, number of hatching and hatched blastocysts on E4.5, embryo arrest and degeneration) were assessed for each of the strain-medium combinations. The results were compared across strains as well as across media. Embryo development depended on both the media and the mouse strain. Embryos from inbred and outbred mice were more sensitive to suboptimal culture conditions compared to the hybrid strain; this was reflected in reduced blastocyst and hatching rates, as well as an increased percentage of arrested and degraded embryos. The choice of optimal media depended strongly on the strain: CSC was better for Balb/c, Sage 1-step for C57Bl/6, while both were preferred for hybrids, and G-TL for outbreds. VitaVitro was quite good for hybrids and performed worse for other strains. Overall, the embryos of each strain behaved differently in different media, and it was not possible to make a real preference for any of them over human embryos based on the results of any single mouse strain. Only a pooled sample of different mouse strains can be used for comprehensive media MEA testing. MEA testing with any strain of mice is doomed to error due to their specific culture requirements. Hybrid mice are too reproductively efficient and cannot be used to distinguish media based on their subtle differences. Outbred and inbred mice are too sensitive and may be delayed or degraded in culture media that is well suited to the requirements of human embryos. Combined analysis of multiple mouse strains should be used to test media more fully and may serve as a model for the heterogeneity of human embryos in IVF clinics.

Culture medium and protein supplementation affect sensitivity of the mouse embryo assay in detecting Triton X-100

RESEARCH QUESTION

To what extent does the type and concentration of protein and the type of culture medium affect the sensitivity of the mouse embryo assay (MEA) to detect Triton X-100 (TX-100) in culture media?

DESIGN

The effect of the concentration of bovine serum albumin (BSA) and human serum albumin (HSA) was assessed by supplementing media with 0.5 or 5 mg/ml. Potassium-supplemented simplex optimized medium (KSOM) and human tubal fluid (HTF) were used as complex and simple formulation media, respectively. Variables were combined, forming study groups where embryos were cultured in test media spiked with a sublethal TX-100 concentration. The conditions of greatest sensitivity were determined by statistical comparison of blastocyst formation rates and total cell counts between groups.

RESULTS

Although all of the study groups showed equal capacity for sustaining proper embryo development, the reported sensitivity of the MEA differed between groups when subjected to TX-100. HTF conferred significantly greater sensitivity than KSOM regardless of the type and concentration of protein used, and medium supplementation with 5 mg/ml BSA rather than 0.5 mg/ml BSA resulted in significantly higher sensitivity regardless of the type of medium used. This increase in concentration also resulted in higher sensitivity when supplementing HTF with HSA. The BSA groups provided more sensitivity than their HSA counterparts, except for the KSOM + 0.5 mg/ml BSA group. Cell count analysis did not provide further significant conclusions.

CONCLUSIONS

For TX-100 detection within culture medium, the type and concentration of protein and the type of culture medium have a direct effect on MEA sensitivity. These results could help to standardize the MEA protocol, and increase its ability to detect sublethal concentrations of embryotoxic substances, especially TX-100, thus avoiding possible clinical harmful effects.

Single-embryo transcriptomic atlas of oxygen response reveals the critical role of HIF-1α in prompting embryonic zygotic genome activation

Adaptive response to physiological oxygen levels (physO2; 5% O2) enables embryonic survival in a low-oxygen developmental environment. However, the mechanism underlying the role of physO2 in supporting preimplantation development, remains elusive. Here, we systematically studied oxygen responses of hallmark events in preimplantation development. Focusing on impeded transcriptional upregulation under atmospheric oxygen levels (atmosO2; 20% O2) during the 2-cell stage, we functionally identified a novel role of HIF-1α in promoting major zygotic genome activation by serving as an oxygen-sensitive transcription factor. Moreover, during blastocyst formation, atmosO2 impeded H3K4me3 and H3K27me3 deposition by deregulating histone-lysine methyltransferases, thus impairing X-chromosome inactivation in blastocysts. In addition, we found atmosO2 impedes metabolic shift to glycolysis before blastocyst formation, thus resulting a low-level histone lactylation deposition. Notably, we also reported an increased sex-dimorphic oxygen response of embryos upon preimplantation development. Together, focusing on genetic and epigenetic events that are essential for embryonic survival and development, the present study advances current knowledge of embryonic adaptive responses to physO2, and provides novel insight into mechanism underlying irreversibly impaired developmental potential due to a short-term atmosO2 exposure.

Nuclear Distribution of the Chromatin-Remodeling Protein ATRX in Mouse Early Embryos during Normal Development and Developmental Arrest In Vitro

The chromatin-remodeling protein ATRX, which is currently recognized as one of the key genome caretakers, plays an important role in oogenesis and early embryogenesis in mammals. ATRX distribution in the nuclei of mouse embryos developing in vivo and in vitro, including when the embryos are arrested at the two-cell stage-the so-called two-cell block in vitro-was studied using immunofluorescent labeling and FISH. In normally developing two- and four-cell embryos, ATRX was found to be closely colocalized with pericentromeric DNA sequences detected with a probe to the mouse major satellite DNA. The association of ATRX with pericentromeric heterochromatin is mediated by nuclear actin and reduced after the treatment of embryos with latrunculin B. When culturing embryos in vitro, the distribution pattern of ATRX changes, leading to a decrease in the association of this protein with major satellite DNA especially under the two-cell block in vitro. Taken together, our data suggest that the intranuclear distribution of ATRX reflects the viability of mouse embryos and their probability of successful preimplantation development.

Mammalian embryo culture media: now and into the future

For over 70years, since the culture of the first mammalian embryo in vitro , scientists have undertaken studies to devise and optimise media to support the manipulation and culture of gametes and embryos. This area of research became especially active in the late 1970s onwards following the successful birth of the first human in vitro fertilised embryo. This review summarises some of the key advances in mammalian embryo culture media over time based on a greater understanding of the biochemical milieu of the reproductive tract. It highlights how learnings from studies in mice and agricultural species have informed human culture media compositions, in particular the inclusion of albumin, growth factors, cytokines, and antioxidants into contemporary culture media formulations, and how these advances may then in turn help to inform and guide development of in vitro culture systems used in other arenas, in particular agriculture. Additionally, it will highlight how the introduction of new technologies, such as timelapse, can influence current trends in media composition and usage that may see a return to a single step medium.

Dynamic metabolism during early mammalian embryogenesis

Dynamic metabolism is exhibited by early mammalian embryos to support changing cell fates during development. It is widely acknowledged that metabolic pathways not only satisfy cellular energetic demands, but also play pivotal roles in the process of cell signalling, gene regulation, cell proliferation and differentiation. Recently, various new technological advances have been made in metabolomics and computational analysis, deepening our understanding of the crucial role of dynamic metabolism during early mammalian embryogenesis. In this Review, we summarize recent studies on oocyte and embryo metabolism and its regulation, with a particular focus on its association with key developmental events such as fertilization, zygote genome activation and cell fate determination. In addition, we discuss the mechanisms of certain metabolites that, in addition to serving as energy sources, contribute to epigenetic modifications.

Making and selecting the best embryo in the laboratory

Over the past 4 decades our ability to maintain a viable human embryo in vitro has improved dramatically, leading to higher implantation rates. This has led to a notable shift to single blastocyst transfer and the ensuing elimination of high order multiple gestations. Future improvements to embryo culture systems will not only come from new improved innovative media formulations (such as the inclusion of antioxidants), but plausibly by moving away from static culture to more dynamic perfusion-based systems now made a reality owing to the breakthroughs in three-dimensional printing technology and micro fabrication. Such an approach has already made it feasible to create high resolution devices for intracytoplasmic sperm injection, culture, and cryopreservation, paving the way not only for improvements in outcomes but also automation of assisted reproductive technology. Although improvements in culture systems can lead to further increases in pregnancy outcomes, the ability to quantitate biomarkers of embryo health and viability will reduce time to pregnancy and decrease pregnancy loss. Currently artificial intelligence is being used to assess embryo development through image analysis, but we predict its power will be realized through the creation of selection algorithms based on the integration of information related to metabolic functions, cell-free DNA, and morphokinetics, thereby using vast amounts of different data types obtained for each embryo to predict outcomes. All of this will not only make assisted reproductive technology more effective, but it will also make it more cost effective, thereby increasing patient access to infertility treatment worldwide.

Glucose promoting the early embryonic development by increasing the lipid synthesis at 2-cell stage

The optimization of culture conditions is one of the main strategies to improve the embryo development competence in in vitro fertilization (IVF). Glucose is an important carbon source while also exists in the oviductal fluid in vivo, the effect of glucose in embryo development microenvironment is still unclear. Here we employed the LC-MS to detect and analyze the metabolites in the culture medium of different cleavage stages including 2-Cell, 4-Cell and 8-Cell mouse embryos, respectively. The effects of the external glucose were estimated by measuring the development rate at different glucose concentrations from 0 to 5 mmol/L, and the gene expression changes were detected to explore the potential mechanism after the addition of glucose in the media. Our results indicated the 2-Cell and 8-Cell stages had defined characteristic metabolites, while 4-Cell stage was the transition state. Global and contiguous metabolic characteristics showed the glycometabolism play a critical role at each early cleavage stages during the embryo development. The 8-Cell rates demonstrated the addition of glucose in culture media significantly improve the embryo competence, the highest rate was 87.33% using 3 mmol/L glucose in media, in contrast only 9.95% using the media without glucose. Meanwhile, the blocked embryos were mainly enriched at 2-Cell stage. Further transcriptome study found 3 mmol/L glucose in media remarkably upregulated the gene expression of lipid biosynthesis at 2-Cell stage, the increased lipid was confirmed by nile red staining. These data indicated the glucose may promote the development competence through increasing the lipid biosynthesis to overcoming the 2-Cell block. Our findings were helpful for the further optimization of IVF culture media, as well as the estimation of embryo quality using metabolites in the culture media.

Modelling the equilibrium partitioning of low concentrations of airborne volatile organic compounds in human IVF laboratories

RESEARCH QUESTION

Can volatile organic compounds (VOC) be modelled in an IVF clinical setting?

DESIGN

The study performed equilibrium modelling of low concentrations of airborne VOC partitioning from the air phase into the oil cover layer into the water-based culture media and into/onto the embryo (air-oil-water-embryo). The air-phase VOC were modelled based on reported VOC concentrations found in modern assisted reproductive technology (ART) suites, older IVF clinics, and hospitals, as well as at 10 parts per billion (ppb) and 100 ppb for all compounds. The modelling was performed with 23 documented healthcare-specific VOC.

RESULTS

Based on the partitioning model, seven compounds (acrolein, formaldehyde, phenol, toluene, acetaldehyde, ethanol and isopropanol) should be of great concern to the embryologist and clinician. Acrolein, formaldehyde, phenol, toluene and acetaldehyde are the VOC with the most potent cytotoxic factor and the highest toxic VOC concentration in media. In addition, ethanol and isopropanol are routinely found in the greatest air-phase concentrations and modelled to have the highest water-based culture concentrations.

CONCLUSIONS

The results of the equilibrium partitioning modelling of VOC provides a fundamental understanding of how airborne VOC partition from the air phase and negatively influence human IVF outcomes. The results presented here are based on the theoretical model and the values presented have not yet been measured in a laboratory or clinical setting. High air-phase concentrations and toxic concentrations of VOC in culture media are likely indicators of poor clinical outcomes. Based on this model, improved air quality in IVF laboratories reduces the chemical burden imparted on embryos, which supports findings of improved IVF outcomes with reduced air-phase VOC concentrations.

Effects of embryonic stem cell-conditioned medium on the preimplantation development of mouse embryos

The production of high-quality embryos in the laboratory and a successful pregnancy are closely related to the condition and contents of oocyte and embryo culture media. In this study, we investigated the effects of embryonic stem cell-conditioned medium (ESCCM) and embryonic stem cells growth medium (ESCGM) compared with potassium-enriched simplex optimized medium (KSOM) on preimplantation embryo development stages during natural or in vitro fertilization (IVF). Birth rate of pups was measured. To obtain mature oocytes, and 2-cell and 8-cell embryos, human chorionic gonadotropin (HCG) was injected 48 h after i.p. injection of 5 units of pregnant mare serum gonadotropin. Mature oocytes were obtained from non-mated female mice 14 h after HCG injection. To obtain 2-cell and 8-cell embryos, mated female mice, 1 day and 3 days, respectively, after HCG injection, were used. Mature oocytes were fertilized in HTF medium. Embryos obtained from natural or in vitro fertilization were cultured in experimental media, ESCCM and ESCGM, or KSOM as the control culture medium. Embryos that developed to the blastocyst stage were transferred to the uteri of pseudopregnant mice and effects of the experimental media on embryo viability were determined. ESCCM and ESCGM could not pass the embryo after the 2-cell stage, but they were suitable for the development of the embryo from the 8-cell stage to the blastocyst. It can be concluded that the embryo has various requirements at different stages of development.

DNA damage in preimplantation embryos and gametes: specification, clinical relevance and repair strategies

BACKGROUND

DNA damage is a hazard that affects all cells of the body. DNA-damage repair (DDR) mechanisms are in place to repair damage and restore cellular function, as are other damage-induced processes such as apoptosis, autophagy and senescence. The resilience of germ cells and embryos in response to DNA damage is less well studied compared with other cell types. Given that recent studies have described links between embryonic handling techniques and an increased likelihood of disease in post-natal life, an update is needed to summarize the sources of DNA damage in embryos and their capacity to repair it. In addition, numerous recent publications have detailed novel techniques for detecting and repairing DNA damage in embryos. This information is of interest to medical or scientific personnel who wish to obtain undamaged embryos for use in offspring generation by ART.

OBJECTIVE AND RATIONALE

This review aims to thoroughly discuss sources of DNA damage in male and female gametes and preimplantation embryos. Special consideration is given to current knowledge and limits in DNA damage detection and screening strategies. Finally, obstacles and future perspectives in clinical diagnosis and treatment (repair) of DNA damaged embryos are discussed.

SEARCH METHODS

Using PubMed and Google Scholar until May 2021, a comprehensive search for peer-reviewed original English-language articles was carried out using keywords relevant to the topic with no limits placed on time. Keywords included ‘DNA damage repair’, ‘gametes’, ‘sperm’, ‘oocyte’, ‘zygote’, ‘blastocyst’ and ‘embryo’. References from retrieved articles were also used to obtain additional articles. Literature on the sources and consequences of DNA damage on germ cells and embryos was also searched. Additional papers cited by primary references were included. Results from our own studies were included where relevant.

OUTCOMES

DNA damage in gametes and embryos can differ greatly based on the source and severity. This damage affects the development of the embryo and can lead to long-term health effects on offspring. DDR mechanisms can repair damage to a certain extent, but the factors that play a role in this process are numerous and altogether not well characterized. In this review, we describe the multifactorial origin of DNA damage in male and female gametes and in the embryo, and suggest screening strategies for the selection of healthy gametes and embryos. Furthermore, possible therapeutic solutions to decrease the frequency of DNA damaged gametes and embryos and eventually to repair DNA and increase mitochondrial quality in embryos before their implantation is discussed.

WIDER IMPLICATIONS

Understanding DNA damage in gametes and embryos is essential for the improvement of techniques that could enhance embryo implantation and pregnancy success. While our knowledge about DNA damage factors and regulatory mechanisms in cells has advanced greatly, the number of feasible practical techniques to avoid or repair damaged embryos remains scarce. Our intention is therefore to focus on strategies to obtain embryos with as little DNA damage as possible, which will impact reproductive biology research with particular significance for reproductive clinicians and embryologists.

Creation, effects on embryo quality, and clinical outcomes of a new embryo culture medium with 31 optimized components derived from human oviduct fluid: A prospective multicenter randomized trial

Purpose

Our aim is to make an ideal embryo culture medium close to human oviduct fluid (HOF) components, and to evaluate the quality of this medium with embryo quality and clinical outcomes in assisted reproductive technology (ART) by a prospective randomized controlled trial (RCT).

Methods

Study I: HOF was collected laparoscopically from patients (n = 28) with normal pelvic findings. According to HOF analysis results, the new medium "HiGROW OVIT®" (OVIT) was designed. Study II: Embryos (2 pronuclei (2PN) = 9633) were assigned from 1435 patients. The blastulation rate (BR), good BR (gBR), utilized (transferred/cryo-preserved) BR (uBR), pregnancy rate (PR), and miscarriage rate (MR) were compared between the OVIT and control groups by RCT.

Results

The novel medium 'OVIT' was produced according to 31 HOF components. The concentrations of essential amino acids (e-AAs) were lower in OVIT than in current media, yet the opposite was true for ne-AA concentrations. gBR and uBR were higher in the OVIT group than in the control group. In the older female group, gBT and uBR were significantly higher in the OVIT group.

Conclusions

The novel medium 'OVIT' was produced according to HOF data. The OVIT had significantly better embryo quality and clinical outcomes than the current media.

Redox Regulation and Oxidative Stress in Mammalian Oocytes and Embryos Developed In Vivo and In Vitro

Oocytes and preimplantation embryos require careful regulation of the redox environment for optimal development both in vivo and in vitro. Reactive oxygen species (ROS) are generated throughout development as a result of cellular metabolism and enzyme reactions. ROS production can result in (i) oxidative eustress, where ROS are helpful signalling molecules with beneficial physiological functions and where the redox state of the cell is maintained within homeostatic range by a closely coupled system of antioxidants and antioxidant enzymes, or (ii) oxidative distress, where excess ROS are deleterious and impair normal cellular function. in vitro culture of embryos exacerbates ROS production due to a range of issues including culture-medium composition and laboratory culture conditions. This increase in ROS can be detrimental not only to assisted reproductive success rates but can also result in epigenetic and genetic changes in the embryo, resulting in transgenerational effects. This review examines the effects of oxidative stress in the oocyte and preimplantation embryo in both the in vivo and in vitro environment, identifies mechanisms responsible for oxidative stress in the oocyte/embryo in culture and approaches to reduce these problems, and briefly examines the potential impacts on future generations.

Effect of sequential versus single-step culture medium on IVF treatments, including embryo and clinical outcomes: a prospective randomized study

PURPOSE

Sequential media G5 series (Vitrolife) and single-step medium Continuous Single Culture Complete (CSC-C) (Irvine Scientific) are two different culture media. We want to examine difference between culturing effects of the two media.

METHODS

To compare the fertilization and early embryo development, a prospective randomized controlled trial with sibling oocytes in infertile patients, aged ≤ 45 years with ≥ 8 oocytes (226 cycles) was conducted. Each half of the retrieved oocytes from the same patient were randomly allocated to two culture media separately. The remaining fresh cycles were randomly assigned to two culture media during the same period (179 cycles). We compared the clinical outcomes based on the total fresh ET cycles in this periods, in which the transferred embryos were only from one culture medium.

RESULTS

Embryo outcomes: 226 cycles, included 176 IVF and 50 ICSI cycles, were analyzed, which correspond to 3518 inseminated or micro-injected oocytes. Clinical outcomes: 71 (CSC-C) and 71 (G5 series) fresh ET cycles were compared. There were no significant differences in clinical outcomes and general fertilization rate. However, the fertilization rate was superior in the CSC-C when compared with G5 in ICSI cycles (76.51% vs. 67.25%, P = 0.008). In addition, the compacted embryo development rate was significantly higher in CSC-C on day 3. The cycles that had compacted embryos on day 3 demonstrated better outcomes both in embryos as well as clinically.

CONCLUSIONS

CSC-C had higher fertilization rates than G5 series in ICSI cycles. In addition, the compaction rates of day 3 embryos were significantly higher in CSC-C.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

Toward a predictive theoretical model for osmolality rise with non-humidified incubation: a randomized, multivariate response-surface study

STUDY QUESTION

What factors associated with embryo culture techniques contribute to the rate of medium osmolality change over time in an embryo culture incubator without added humidity?

SUMMARY ANSWER

The surface area-to-volume ratio of culture medium (surface area of the medium exposed to an oil overlay), as well as the density and height of the overlaying oil, all interact in a quantitative way to affect the osmolality rise over time.

WHAT IS KNOWN ALREADY

Factors such as medium volume, different oil types, and associated properties, individually, can affect osmolality change during non-humidified incubation.

STUDY DESIGN, SIZE, DURATION

Several experimental designs were used, including simple single-factor completely randomized designs, as well as a multi-factor response surface design. Randomization was performed at one or more levels for each experiment. Osmolality measurements were performed over 7 days, with up to 8 independent osmolality measurements performed per treatment group over that time. For the multi-factor study, 107 independent combinations of factor levels were assessed to develop the mathematical model.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study was conducted in a research laboratory setting. Commercially available embryo culture medium and oil was used. A MINC incubator without water for humidification was used for the incubation. Osmolality was measured with a vapor pressure osmometer after calibration. Viscometry and density were conducted using a rheometer, and volumetric flasks with an analytical balance, respectively. Data analyses were conducted with several commercially available software programs.

MAIN RESULTS AND THE ROLE OF CHANCE

Preliminary experiments showed that the surface area-to-volume ratio of the culture medium, oil density, and oil thickness above the medium all contributed significantly (P < 0.05) to the rise in osmolality. A multi-factor experiment showed that a combination of these variables, in the form of a truncated cubic polynomial, was able to predict the rise in osmolality, with these three variables interacting in the model (P < 0.05). Repeatability, as measured by the response of identical treatments performed independently, was high, with osmolality values being ± 2 of the average in most instances. In the final mathematical model, the terms of the equation were significant predictors of the outcome, with all P-values being significant, and only one P-value > 0.0001.

LIMITATIONS, REASONS FOR CAUTION

Although the range of values for the variables were selected to encompass values that are expected to be encountered in usual embryo culture conditions, variables outside of the range used may not result in accurate model predictions. Although the use of a single incubator type and medium type is not expected to affect the conclusions, that remains an uncertainty.

WIDER IMPLICATIONS OF THE FINDINGS

Using this predictive model will help to determine if one should be cautious in using a specific system and will provide guidance on how a system may be modified to provide improved stability during embryo culture.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by Cook Medical. The author is a Team Lead and Senior Scientist at Cook Medical. The author has no other conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Lysine Deprivation during Maternal Consumption of Low-Protein Diets Could Adversely Affect Early Embryo Development and Health in Adulthood

The conversion of lysine to glutamate is needed for signaling in all plants and animals. In mouse embryonic stem (mES) cells, and probably their progenitors, endogenous glutamate production and signaling help maintain cellular pluripotency and proliferation, although the source of glutamate is yet to be determined. If the source of glutamate is lysine, then lysine deprivation caused by maternal low-protein diets could alter early embryo development and, consequently, the health of the offspring in adulthood. For these reasons, we measured three pertinent variables in human embryonic stem (hES) cells as a model for the inner cell masses of human blastocysts. We found that RNA encoding the alpha-aminoadipic semialdehyde synthase enzyme, which regulates glutamate production from lysine, was highly expressed in hES cells. Moreover, the mean amount of lysine consumed by hES cells was 50% greater than the mean amount of glutamate they produced, indicating that lysine is likely converted to glutamate in these cells. Finally, hES cells expressed RNA encoding at least two glutamate receptors. Since this may also be the case for hES progenitor cells in blastocysts, further studies are warranted to verify the presence of this signaling process in hES cells and to determine whether lysine deprivation alters early mammalian embryo development.

Mouse embryos exposed to oxygen concentrations that mimic changes in the oviduct and uterus show improvement in blastocyst rate, blastocyst size, and accelerated cell division

After in vivo fertilisation, the preimplantation embryo goes through cleavage during migration along the oviduct in mammals or the fallopian tube in a woman and ends up inside the uterus. This study investigates the effect of a protocol aimed at closely reproducing that natural oxygen concentration in the oviduct (7 % O2 from day 1 to day 3 and 2 % from day 3 to day 5), in contrast to the concentrations (5 % or 20 %) widely used in practice in ART using morphokinetic. Female mice (BI6/CBAca) were sacrificed, and zygotes were isolated 20 h after mating and randomly allocated to three parallel groups, which were grown under high atmospheric, low, or sequential oxygen concentrations. Zygotes were cultured in GTL medium (Vitrolife) and observed by the Primovision time-lapse system. Blastocyst rate at 120 h in the sequential group (91.3 %) was significantly increased over the high (76.3 %) and low (74.4 %) groups. Blastocyst size was also enlarged in the sequential group compared to the high and low groups. Moreover, cell division in the sequential group was significantly faster at almost every cleavage stage than it was in the other groups. Notably, the duration of the interims between stages also differed significantly between the groups. This study demonstrated that, in comparison to routinely used high or low oxygen conditions, oxygen concentrations mimicking changes in the oviduct and uterus significantly improve the blastocyst rate and size and accelerate cell division at several stages as well as the interims between cleavage events.

H4K20 monomethylation inhibition causes loss of genomic integrity in mouse preimplantation embryos

Maintaining genomic integrity in mammalian early embryos, which are deficient in DNA damage repair, is critical for normal preimplantation and subsequent development. Abnormalities in DNA damage repair in preimplantation embryos can cause not only developmental arrest, but also diseases such as congenital disorders and cancers. Histone H4 lysine 20 monomethylation (H4K20me1) is involved in DNA damage repair and regulation of gene expression. However, little is known about the role of H4K20me1 during mouse preimplantation development. In this study, we revealed that H4K20me1 mediated by SETD8 is involved in maintaining genomic integrity. H4K20me1 was present throughout preimplantation development. In addition, reduction in the level of H4K20me1 by inhibition of SETD8 activity or a dominant-negative mutant of histone H4 resulted in developmental arrest at the S/G2 phase and excessive accumulation of DNA double-strand breaks. Together, our results suggest that H4K20me1, a type of epigenetic modification, is associated with the maintenance of genomic integrity and is essential for preimplantation development. A better understanding of the mechanisms involved in maintaining genome integrity during preimplantation development could contribute to advances in reproductive medicine and technology.

Type of protein supplement in cryopreservation solutions impacts on the degree of ultrastructural damage in frozen-thawed human oocytes

Protein sources used as supplements of IVF culture media are known to have several implications for the function and stability of embryo culture environment. In fact, they i) transport biologically active molecules ii) chelate heavy metals, iii) regulate media pH, iii) scavenge reactive oxygen species (ROS) and iv) attenuate osmotic stress to which cells are exposed in sub-optimal culture conditions. Instead, their specific relevance to the formulation of cryopreservation solutions used for gamete and embryo cryopreservation remains uncertain. In the present work, we tested the hypothesis that different protein supplements present in cryopreservation solutions, serum or plasma protein solution (PPS), or different concentrations of the same supplement (serum), are associated with different types and/or magnitude of cryopreservation-derived cell damage. To this end, using cryopreservation solutions containing serum or PPS, donated supernumerary human mature oocytes were frozen-thawed by slow freezing and compared with fresh controls. Ultrastructural markers of oocyte quality were adopted as objective measure to assess possible damage from cryopreservation. The study results indicate that the adoption of serum minimises cell damage induced by cryopreservation. Indeed, typical hallmarks of cryodamage in human oocytes, i.e. loss of cortical granules, zona pellucida hardening and above all vacuolization, were largely reduced in oocytes cryopreserved with solutions containing serum, especially if used a higher concentration. This suggest that oocyte cryopreservation still has significant margins of improvement that may derive also from composition of cryopreservation media.

Systematic Development, Validation and Optimization of a Human Embryo Culture System

Objective: To develop and validate a reliable in vitro culture system for human embryos. Design: Retrospective analyses of a series of four studies were conducted between 2006 and 2010 to assess the effect of incubator type (CO2 box versus Tri-gas minibox), media type, oil type, and hyaluronate supplementation. Optimization of in vitro blastocyst development was verified by assessing our National CDC/ART Surveillance reports between 2010 and 2016. Material and Methods: All patients experienced controlled ovarian hyperstimulation, followed by egg retrieval 35 h post-hCG. Cumulus-oocyte complexes were temporarily cultured in P1 or LG Fert medium plus HSA. Eggs were moved to a more complex media (G-medium or Global®-LG medium) containing a synthetic protein and embryo adhesion supplement (SPS and EAS, respectively; mLG) post-ICSI insemination. Zygotes were assigned to group culture in 25 µl droplets under oil (light mineral oil or paraffin oil; 37 °C) and embryo development was evaluated on Days 3, 5, and 6 and transferred on Day 3 to 5 depending on the number/quality of embryos available and the IVF history of the patient. Transfers were performed under ultrasound guidance, primarily using a Sureview-Wallace catheter, and enriched ET medium containing 500 µg/mL EAS. Results: Pilot study results (Expt. 1) showed that a mLG single-step medium could be effectively used in combination with Sanyo MCO-5 tri-gas (TG) incubators. Once adapted to SCIRS Lab in 2007 (Expt. 2), the latter culture system yielded improved blastocyst production and pregnancy outcomes compared to CO2 in air sequential incubation in P1/Multi-blast medium. In Expt. 3, the mLG/TG system yielded high levels of ≥2BB quality blastocysts (51 to 66%) across all age groups, and greater (p < 0.05) pregnancy success/live birth rates using fewer embryos transferred on Day 5 versus Day 3. After validating its clinical effectiveness, mLG was then prospectively compared to a new generation G-media (1.5 & 2.5; Expt. 4) and determined that the crossover treatment using paraffin oil (Ovoil™) allowed the mLG system to be optimized. Subsequently, a compilation of our Annual CDC/ART reported data over six years verified the overall viability of in vitro cultured and vitrified blastocysts produced in the mLG/TG system. Conclusion: By systematically evaluating and implementing various components of an embryo culture system we were able to optimize blastocyst development over the last decade. Our mLG/TG culture system modified an exceptionally well designed KSOMAA LG medium using endotoxin-free EAS and SPS additives to support cellular membrane wellness under stressful in vitro conditions (e.g., culture, cell biopsy, vitrification). Our use of the mLG/TG culture system has proven to be effective, creating reliably high blastocyst production, implantation, and healthy live births.

Comprehensive analysis of whole genome methylation in mouse blastocysts cultured with four different constituents following in vitro fertilization

Background

With the development of assisted reproductive technology (ART), diseases believed to be caused by ART have begun to be identified as imprinted disease. However, no conclusion has been reached. So we sought to determine whether ART procedures disturb gene methylation and whether imprinted genes alone are selectively disturbed. To examine whether the constituents of the culture medium contribute to the changes in methylation, we used a mouse model to conduct IVF and comprehensively analyzed 5′–C–phosphate–G–3′ (CpG) by reduced representation bisulfite sequencing (RRBS) using a second-generation sequencer to determine changes in methylation using four types of culture media with different amino acid constituents.

Results

We cultured ova to the blastocyst stage in a mouse model in culture media with four different amino acid constituents. Each culture medium included (1) KSOM culture medium (NoAA), (2) KSOM media + essential amino acids (EAAs), (3) KSOM medium + non-essential amino acids (NEAAs), or (4) KSOM medium + EAAs + NEAAs (AllAA) analyzed by reduced representation bisulfite sequencing. The results showed that (1) there were many regions that maintained hypermethylation with NEAAs, (2) there was little effect of demethylation on reprogramming in the 5′UTR and promoter regions, and (3) specific changes were observed in imprinted genes such as Nnat and Nespas.

Conclusions

Compared with EAAs, NEAAs could protect genes from demethylation caused by reprogramming. On the imprinted genes, methylation of the promoter region of H19 was decreased by NEAAs, suggesting that specific genes were prone to changes in methylation. It was suggested that these changes could provide similar results in humans. Further studies are needed to understand how changes in methylation may affect gene expression profiles.

Effects of dynamic oxygen concentrations on the development of mouse pre- and peri-implantation embryos using a double-channel gas supply incubator system

Objective

We aimed to evaluate the effects of different oxygen conditions (20% [high O₂], 5% [low O₂] and 5% decreased to 2% [dynamic O₂]) on mouse pre- and peri-implantation development using a novel double-channel gas supply (DCGS) incubator (CNC Biotech Inc.) to alter the oxygen concentration during in vitro culture.

Methods

The high-O₂ and low-O₂ groups were cultured from the one-cell to the blastocyst stage under 20% and 5% oxygen concentrations, respectively. In the dynamic-O₂ group, mouse embryos were cultured from the one-cell to the morula stage under 5% O₂ for 3 days, followed by culture under 2% O₂ to the blastocyst stage. To evaluate peri-implantation development, the blastocysts from the three groups were individually transferred to a fibronectin-coated dish and cultured to the outgrowth stage in droplets.

Results

The blastocyst formation rate was significantly higher in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group. The total cell number was significantly higher in the dynamic-O₂ group than in the low-O₂ and high-O₂ groups. Additionally, the apoptotic index was significantly lower in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group. The trophoblast outgrowth rate and spread area were significantly higher in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group.

Conclusion

Our results showed that a dynamic oxygen concentration (decreasing from 5% to 2%) had beneficial effects on mouse pre- and peri-implantation development. Optimized, dynamic changing of oxygen concentrations using the novel DCGS incubator could improve the developmental competence of in vitro cultured embryos in a human in vitro fertilization and embryo transfer program.

Modeling Mammalian Commitment to the Neural Lineage Using Embryos and Embryonic Stem Cells

Early mammalian embryogenesis relies on a large range of cellular and molecular mechanisms to guide cell fate. In this highly complex interacting system, molecular circuitry tightly controls emergent properties, including cell differentiation, proliferation, morphology, migration, and communication. These molecular circuits include those responsible for the control of gene and protein expression, as well as metabolism and epigenetics. Due to the complexity of this circuitry and the relative inaccessibility of the mammalian embryo in utero, mammalian neural commitment remains one of the most challenging and poorly understood areas of developmental biology. In order to generate the nervous system, the embryo first produces two pluripotent populations, the inner cell mass and then the primitive ectoderm. The latter is the cellular substrate for gastrulation from which the three multipotent germ layers form. The germ layer definitive ectoderm, in turn, is the substrate for multipotent neurectoderm (neural plate and neural tube) formation, representing the first morphological signs of nervous system development. Subsequent patterning of the neural tube is then responsible for the formation of most of the central and peripheral nervous systems. While a large number of studies have assessed how a competent neurectoderm produces mature neural cells, less is known about the molecular signatures of definitive ectoderm and neurectoderm and the key molecular mechanisms driving their formation. Using pluripotent stem cells as a model, we will discuss the current understanding of how the pluripotent inner cell mass transitions to pluripotent primitive ectoderm and sequentially to the multipotent definitive ectoderm and neurectoderm. We will focus on the integration of cell signaling, gene activation, and epigenetic control that govern these developmental steps, and provide insight into the novel growth factor-like role that specific amino acids, such as L-proline, play in this process.

Autologous endometrial cell co-culture improves human embryo development to high-quality blastocysts: a randomized controlled trial

RESEARCH QUESTION

Does autologous endometrial cell co-culture (AECC) improve the number of good-quality blastocysts obtained by IVF/intracytoplasmic sperm injection (ICSI), compared with conventional embryo culture medium in a broad group of patients referred to assisted reproductive technology (ART)?

DESIGN

This interventional, randomized, double-blind study took place at Clinique Ovo from March 2013 to October 2015 and included 207 healthy patients undergoing an IVF or ICSI protocol, of which 71 were excluded before randomization. On the previous cycle, all participants underwent an endometrial biopsy at D5 to D7 post-ovulation, following which the endometrial cells were prepared for AECC.

RESULTS

The data demonstrated that AECC significantly increased the incidence of good-quality blastocysts compared with culture in conventional media (42.6% vs 28.4%, P < 0.001). No significant differences were found in pregnancy and live birth rates.

CONCLUSION

This study demonstrated the benefits of AECC on blastocyst quality compared with conventional embryo culture medium, in a broader category of patients referred to ART as opposed to other studies that concentrated on specific causes of infertility only. However, limitations of the study design should be taken into consideration; the analysis was performed using embryos rather than patients and a follow-up of children born following the treatments could not be conducted.

Embryoid Body Differentiation of Mouse Embryonic Stem Cells into Neurectoderm and Neural Progenitors

Mouse embryonic stem cells (mESCs) are pluripotent cells capable of differentiating in vitro to form the ~200 types of cells of the developing embryo and adult, including cells of the nervous system. This makes mESCs a useful tool for studying the molecular mechanisms of mammalian embryonic development. Many protocols involving the use of growth factors and small molecules to differentiate mESCs into neural progenitors and neurons currently exist. However, there is a paucity of protocols available that recapitulate the developmental process. Our laboratory has developed a protocol to recapitulate mammalian neural lineage development by differentiating mESCs to mature neurons via intermediate cell populations observed during in vivo embryo development. This protocol uses the amino acid L-proline to direct the differentiation of mESCs, grown as embryoid bodies, into Sox1⁺ neurectoderm, followed by differentiation to form Nestin⁺, BLBP⁺, and NeuN⁺ neural cell types.

[Impact of air quality on practices and results in the IVF laboratory]

The concept of Air Quality often refers to particulate and microbiological contamination of ambiant air. European Directive 2006/86/CE encompass the IVF process and specify a class A air quality for manipulation of tissue and cells, in a class D environment (A over D rule). Recognizing the paramount importance of ensuring the highest microbiological and particulate safety in the IVF laboratory, it is equally important to take into account practicability issues and the financial burden of these recommendations, as well as the utter need to protect gametes and embryo viability during their IVF journey. The usefulness of such stringent recommendations may also be questionned given the absence of published cases of airborne contaminations and related patients infections after embryo transfer. The European directive stems from pharmaceutical standards and were not specifically designed for human IVF. Gametes and embryos are indeed extremely sensitive to physical and chemical stress and require strict temperature, osmolarity and pH control, as well as an absence of chemical contamination during manipulation and culture. These conditions are hardly obtained when using laminar flow hoods. Following concerns raised by many experts in the field, exceptions to the A over D rule were added in the 2006/86/CE Directives. This narrative review discusses all these aspects in a critical way and compare scientific and legal requirements applying to IVF practices in different regions of the world.

Cairo consensus on the IVF laboratory environment and air quality: report of an expert meeting

This proceedings report presents the outcomes from an international Expert Meeting to establish a consensus on the recommended technical and operational requirements for air quality within modern assisted reproduction technology (ART) laboratories. Topics considered included design and construction of the facility, as well as its heating, ventilation and air conditioning system; control of particulates, micro-organisms (bacteria, fungi and viruses) and volatile organic compounds (VOCs) within critical areas; safe cleaning practices; operational practices to optimize air quality while minimizing physicochemical risks to gametes and embryos (temperature control versus air flow); and appropriate infection-control practices that minimize exposure to VOC. More than 50 consensus points were established under the general headings of assessing site suitability, basic design criteria for new construction, and laboratory commissioning and ongoing VOC management. These consensus points should be considered as aspirational benchmarks for existing ART laboratories, and as guidelines for the construction of new ART laboratories.

Continuous embryo culture elicits higher blastulation but similar cumulative delivery rates than sequential: a large prospective study

PURPOSE

To assess whether continuous embryo culture involves better embryological and/or clinical outcomes than sequential.

METHODS

Prospective study at a private IVF center. All consecutive IVF cycles (September 2013-2015) fulfilling the inclusion criteria underwent embryo culture in either Continuous-Single-Culture-Media (CSCM, n = 972) or sequential media (Quinn's Advantage, n = 514), respectively. ICSI, blastocyst culture in either standard (MINC) or undisturbed (Embryoscope) incubation, transfer (until September 2016), and pregnancy follow-up (until September 2017) were performed. When aneuploidy testing was required, trophectoderm biopsy and qPCR were performed. Sub-analyses and logistic regression corrected for confounders were performed. The primary outcomes were overall blastocyst rate per oocyte and mean blastocyst rate per cycle. The sample size was defined to reach 95 and 80% statistical power for the former and the latter outcome, respectively. Secondary outcomes were euploidy (if assessed), cumulative delivery rates, gestational age, and birthweight.

RESULTS

Continuous embryo culture resulted into a higher overall blastocyst rate per inseminated oocyte than sequential (n = 2211/5841, 37.9% vs. 1073/3216, 33.4%; p < 0.01), confirmed also from a cycle-based analysis (mean blastocyst rate: 38.7% ± 29.7% vs. 34.3% ± 29.4%; p = 0.01). The continuous media (OR = 1.23), the undisturbed incubation system (OR = 1.22), the maternal age (OR = 0.92), and the sperm factor (OR = 0.85) were outlined as positive predictors of blastulation. However, the cumulative delivery rates per ended cycle (i.e., delivery achieved or no blastocyst produced or left; > 90%) were comparable in the two groups (n = 244/903, 27.0% vs. 129/475, 27.2%). The neonatal outcomes were similar.

CONCLUSIONS

Continuous culture involves better embryological but similar clinical outcomes than sequential. This large prospective study supports the absence of clinical disparity among the two approaches.

[Culture conditions for gametes and embryos: Which culture medium? Which impact on newborn?]

Many studies have examined the impact of cell/embryo culture media on the development of human embryo during IVF process, but few studies have followed up and compared the effects of these culture media on the developmental outcome of children conceived by IVF. As recurrent experimental evidence from animal studies suggests potential long-term effects of embryo culture media on the health outcome of IVF-conceived children, more studies are needed to clarify the role of the culture media and mechanisms underlying such effects. In human, however, the effects of culture media are difficult to pinpoint due to complications stem from both the influence of maternal nutrition during the gestational period and the parental genetic. Based on a simple review of the literature integrating animal experimentations and human clinic studies, we suggest that the composition of culture medium should be considered beyond the character of unique or sequential medium, corresponding to "let embryo choose" or "back to nature" respectively. Instead, we suggest that the main components of embryo culture media should be considered from the point of view of metabolic consequences and potential epigenetic effects. Given that energetic metabolites can regulate epigenetic machinery, we hypothesize that metabolic abnormalities linked to morphological abnormalities could reveal epigenetic defects in embryos.

Serial Culture Is Critical for In Vitro Development of Parthenogenetic Embryos in the Golden Syrian Hamster

Unlike oocytes of many other mammalian species, parthenogenetically activated hamster oocytes have not been reported to develop beyond the two-cell stage. This study investigated the in vitro development into blastocysts of parthenogenetic embryos of Golden Syrian hamsters. We observed that hamster oocytes could easily be artificially activated (AA) by treatment with ionomycin plus 6-dimethylaminopurine + cycloheximide + cytochalasin B as assessed by embryo cleavage in HECM-9 (63.15%) or HECM-10 (63.82%). None of the cleaved embryos developed beyond the two-cell stage when cultured in either of the two media. However, some of the embryos overcame the two-cell block and developed to the blastocyst stage (26.45%) when they were first cultured in HECM-10 for 24 hours and then in HECM-9 (serial culture media HECM-10-9) for 72 hours. Blastocyst development was further significantly (66.2%) improved when embryos were cultured in HECM-10 supplemented with ethylenediaminetetraacetic acid for 24 hours, then in HECM-9 supplemented with glucose for 72 hours (serial culture media HECM-11a-b). Hamster oocytes activated with ionomycin, ethanol, or a combination of the two treatments would develop to the blastocyst stage in serial culture media HECM-11a-b, whereas none of the spontaneously activated oocytes cleaved (0% vs. 86.93%, p < 0.05). DNA and microtubule configurations of spontaneously activated and AA oocytes were assessed by immunocytochemical staining and fluorescence microscopy. The results indicate that serial culture and the method of activation are critical for overcoming the in vitro developmental block of hamster parthenogenetic embryos. This study is the first to report blastocyst development from parthenogenetically activated hamster oocytes.

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.

Insulin and branched-chain amino acid depletion during mouse preimplantation embryo culture programmes body weight gain and raised blood pressure during early postnatal life

Mouse maternal low protein diet exclusively during preimplantation development (Emb-LPD) is sufficient to programme altered growth and cardiovascular dysfunction in offspring. Here, we use an in vitro model comprising preimplantation culture in medium depleted in insulin and branched-chain amino acids (BCAA), two proposed embryo programming inductive factors from Emb-LPD studies, to examine the consequences for blastocyst organisation and, after embryo transfer (ET), postnatal disease origin. Two-cell embryos were cultured to blastocyst stage in defined KSOM medium supplemented with four combinations of insulin and BCAA concentrations. Control medium contained serum insulin and uterine luminal fluid amino acid concentrations (including BCAA) found in control mothers from the maternal diet model (N-insulin + N-bcaa). Experimental medium (three groups) contained 50% reduction in insulin and/or BCAA (L-insulin + N-bcaa, N-insulin + L-bcaa, and L-insulin + N-bcaa). Lineage-specific cell numbers of resultant blastocysts were not affected by treatment. Following ET, a combined depletion of insulin and BCAA during embryo culture induced a non sex-specific increase in birth weight and weight gain during early postnatal life. Furthermore, male offspring displayed relative hypertension and female offspring reduced heart/body weight, both characteristics of Emb-LPD offspring. Combined depletion of metabolites also resulted in a strong positive correlation between body weight and glucose metabolism that was absent in the control group. Our results support the notion that composition of preimplantation culture medium can programme development and associate with disease origin affecting postnatal growth and cardiovascular phenotypes and implicate two important nutritional mediators in the inductive mechanism. Our data also have implications for human assisted reproductive treatment (ART) practice.

•

Chronic disease may derive from maternal undernutrition during pregnancy, including the periconceptional period.

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Mouse embryos cultured in medium low in insulin and select amino acids gave rise to offspring with disease symptoms.

•

We propose these metabolite deficiencies around conception induce adverse programming of the early embryo leading to increased disease risk in later life.

Single versus sequential culture medium: which is better at improving ongoing pregnancy rates? A systematic review and meta-analysis

This study aimed to evaluate if single medium is better than sequential medium at improving ongoing pregnancy rates in patients undergoing assisted reproductive technology (ART) procedures. The data featured in this meta-analysis were extracted from four randomized controlled trials yielded from a systematic search carried out on electronic databases. The primary endpoint was ongoing pregnancy rate. Secondary endpoints included clinical pregnancy and miscarriage rates. The endpoints for ongoing pregnancy rate were also analyzed based on the time at which the embryo transfers were performed: cleavage stage (day 2/3) and/or blastocyst stage (day 5/6). There were no significant differences between single and sequential medium for clinical pregnancy (RR=1.09; 95%CI=0.83-1.44; p=0.53), ongoing pregnancy (RR=1.11; 95%CI=0.87-1.40; p=0.39), or miscarriage rates (RR=0.89; 95%CI=0.44-1.81; p=0.74). No significant difference was found for ongoing pregnancy rate (RR=1.29; 95%CI=0.93-1.78; p=0.12) between single and sequential medium when only trials in which embryos were transferred at the blastocyst stage were included. In conclusion, the choice of embryo culture approach - single or sequential medium - did not affect the ongoing pregnancy rates of patients undergoing ART cycles.

Nutrition and maternal metabolic health in relation to oocyte and embryo quality: critical views on what we learned from the dairy cow model

Although fragmented and sometimes inconsistent, the proof of a vital link between the importance of the physiological status of the mother and her subsequent reproductive success is building up. High-yielding dairy cows are suffering from a substantial decline in fertility outcome over past decades. For many years, this decrease in reproductive output has correctly been considered multifactorial, with factors including farm management, feed ratios, breed and genetics and, last, but not least, ever-rising milk production. Because the problem is complex and requires a multidisciplinary approach, it is hard to formulate straightforward conclusions leading to improvements on the 'work floor'. However, based on remarkable similarities on the preimplantation reproductive side between cattle and humans, there is a growing tendency to consider the dairy cow's negative energy balance and accompanying fat mobilisation as an interesting model to study the impact of maternal metabolic disorders on human fertility and, more specifically, on oocyte and preimplantation embryo quality. Considering the mutual interest of human and animal scientists studying common reproductive problems, this review has several aims. First, we briefly introduce the 'dairy cow case' by describing the state of the art of research into metabolic imbalances and their possible effects on dairy cow reproduction. Second, we try to define relevant in vitro models that can clarify certain mechanisms by which aberrant metabolite levels may influence embryonic health. We report on recent advances in the assessment of embryo metabolism and meantime critically elaborate on advantages and major limitations of in vitro models used so far. Finally, we discuss hurdles to be overcome to successfully translate the scientific data to the field.

Oxygen tension in embryo culture: does a shift to 2% O2 in extended culture represent the most physiologic system?

There has been much debate regarding the optimal oxygen tension in clinical embryo culture. The majority of the literature to date has compared 5% oxygen to atmospheric levels (20-21%). While the majority of modern IVF labs have accepted the superiority of 5% oxygen tension, a new debate has emerged regarding whether a further reduction after day 3 of development represents the most physiologic system. This new avenue of research is based on the premise that oxygen tension is in fact lower in the uterus than in the oviduct and that the embryo crosses the uterotubal junction sometime on day 3. While data are currently limited, recent experience with ultra-low oxygen (2%) after day 3 of development suggests that the optimal oxygen tension in embryo culture may depend on the stage of development. This review article will consider the current state of the literature and discuss ongoing efforts at studying ultra-low oxygen tension in extended culture.

Composition of single-step media used for human embryo culture

OBJECTIVE

To determine compositions of commercial single-step culture media and test with a murine model whether differences in composition are biologically relevant.

DESIGN

Experimental laboratory study.

SETTING

University-based laboratory.

ANIMAL(S)

Inbred female mice were superovulated and mated with outbred male mice.

INTERVENTION(S)

Amino acid, organic acid, and ions content were determined for single-step culture media: CSC, Global, G-TL, and 1-Step. To determine whether differences in composition of these media are biologically relevant, mouse one-cell embryos were cultured for 96 hours in each culture media at 5% and 20% oxygen in a time-lapse incubator.

MAIN OUTCOME MEASURE(S)

Compositions of four culture media were analyzed for concentrations of 30 amino acids, organic acids, and ions. Blastocysts at 96 hours of culture and cell cycle timings were calculated, and experiments were repeated in triplicate.

RESULT(S)

Of the more than 30 analytes, concentrations of glucose, lactate, pyruvate, amino acids, phosphate, calcium, and magnesium varied in concentrations. Mouse embryos were differentially affected by oxygen in G-TL and 1-Step.

CONCLUSION(S)

Four single-step culture media have compositions that vary notably in pyruvate, lactate, and amino acids. Blastocyst development was affected by culture media and its interaction with oxygen concentration.

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.

[Embryo development in two single-step media: Analysis of 2059 sibling oocytes]

OBJECTIVE

The aim of this study was to compare embryo development cultured in two single-step media commercially available: Fert/Sage One Step® (Origio) and Continuous Single Culture® (CSC) (Irvine Scientific).

METHODS

A prospective auto-controlled study of sibling oocytes from women undergoing conventional in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) was performed in our center from February to June 2015. After fertilization, for every patient, half of oocytes were cultured in the single-step Fert/Sage One Step® (serie SAGE) and the other half in the single-step CSC®(serie CSC). Fertilization and embryo morphology rates were assessed by day 1 to day 5-6 if needed. Embryo presenting<20% of fragmentation and 4 cells at day 2, 8 cells at day 3 were qualified as "top quality". Embryo with<20% of fragmentation and 3-5 cells at day 2, 6-10 cells at day 3 were qualified as "good quality". Blastocyst B3, B4, B5 with A or B inner cell mass and A or B trophectoderm were qualified as "good quality". Transferred or frozen embryos were qualified as useful embryos.

RESULTS

Sixty-two attempts of IVF and 133 of ICSI were analyzed, corresponding to 2059 inseminated or micro-injected oocytes. Fertilization rate were not different between the 2 series, respectively SAGE vs CSC (IVF: 73.4% vs 68.3% [P=0.49]; ICSI: 58.9% vs 63.8% [P=0.12]). No difference was found for embryo morphology, respectively SAGE vs CSC, at day 2 (top quality embryo at day 2 IVF: 34.4% vs 33% [P=0.98]; ICSI: 42.4% vs 44.9% [P=0.37]; and good quality embryo at day 2 IVF: 44% vs 50.2% [P=0.07]; ICSI: 64% vs 71% [P=0.35]); no difference at day 3 (top quality embryo at day 3 IVF: 19.4% vs 21.3% [P=0.61]; ICSI: 28.7% vs 27.4% [P=0.54]; and good quality embryo at day 3 IVF: 40.4% vs 50.2% [P=0.91]; ICSI: 51% vs 47.6% [P=0.47]). Blastocyst development rate were not different, respectively SAGE vs CSC (IVF: 39.9% vs 41.5% [P=0.63] with 42.9% vs 42.2% of good quality blastocyst [P=0.70]; ICSI: 41.1% vs 37.8% [P=0.18] with 32.9% vs 40.8% of good quality blastocyst [P=0.13]). No difference was found in the useful embryo rate in the 2 series SAGE vs CSC (IVF: 52.8% vs 55.2% [P=0.83]; ICSI: 62.4% vs 61.7% [P=0.70]).

CONCLUSION

Embryo development and rate of useful embryos, transferred or frozen, were not different according to the embryo culture in single-step media Fert/Sage One Step® vs single-step Continuous Single Culture®.

Optimizing the culture environment and embryo manipulation to help maintain embryo developmental potential

With increased use of comprehensive chromosome screening (CCS), the question remains as to why some practices do not experience the same high levels of clinical success after implementation of the approach. Indeed, the debate surrounding the efficacy and usefulness of blastocyst biopsy and CCS continues. Importantly, several variables impact the success of an assisted reproductive technology cycle. Transfer of a euploid embryo is but one factor in an intricate system that requires numerous steps to occur successfully. Certainly, the culture environment and the manipulations of the embryo during its time in the laboratory can impact its reproductive potential. Environmental stressors ranging from culture media to culture conditions and even culture platform can impact biochemical, metabolic, and epigenetic patterns that can affect the developing cell independent of chromosome number. Furthermore, accompanying procedures, such as biopsy and vitrification, are complex and, when performed improperly, can negatively impact embryo quality. These are areas that likely still carry room for improvement within the IVF laboratory.

Oxygen-regulated gene expression in murine cumulus cells

Oxygen is an important component of the environment of the cumulus-oocyte complex (COC), both in vivo within the ovarian follicle and during in vitro oocyte maturation (IVM). Cumulus cells have a key role in supporting oocyte development, and cumulus cell function and gene expression are known to be altered when the environment of the COC is perturbed. Oxygen-regulated gene expression is mediated through the actions of the transcription factors, the hypoxia-inducible factors (HIFs). In the present study, the effect of oxygen on cumulus cell gene expression was examined following in vitro maturation of the murine COC at 2%, 5% or 20% oxygen. Increased expression of HIF-responsive genes, including glucose transporter-1, lactate dehydrogenase A and BCL2/adenovirus E1B interacting protein 3, was observed in cumulus cells matured at 2% or 5%, compared with 20% oxygen. Stabilisation of HIF1α protein in cumulus cells exposed to low oxygen was confirmed by western blot and HIF-mediated transcriptional activity was demonstrated using a transgenic mouse expressing green fluorescent protein under the control of a promoter containing hypoxia response elements. These results indicate that oxygen concentration influences cumulus cell gene expression and support a role for HIF1α in mediating the cumulus cell response to varying oxygen.

Noninferiority, randomized, controlled trial comparing embryo development using media developed for sequential or undisturbed culture in a time-lapse setup

OBJECTIVE

To study whether a culture medium that allows undisturbed culture supports human embryo development to the blastocyst stage equivalently to a well-established sequential media.

DESIGN

Randomized, double-blinded sibling trial.

SETTING

Independent in vitro fertilization (IVF) clinics.

PATIENT(S)

One hundred twenty-eight patients, with 1,356 zygotes randomized into two study arms.

INTERVENTION(S)

Embryos randomly allocated into two study arms to compare embryo development on a time-lapse system using a single-step medium or sequential media.

MAIN OUTCOME MEASURE(S)

Percentage of good-quality blastocysts on day 5.

RESULT(S)

Percentage of day 5 good-quality blastocysts was 21.1% (standard deviation [SD] ± 21.6%) and 22.2% (SD ± 22.1%) in the single-step time-lapse medium (G-TL) and the sequential media (G-1/G-2) groups, respectively. The mean difference (-1.2; 95% CI, -6.0; 3.6) between the two media systems for the primary end point was less than the noninferiority margin of -8%. There was a statistically significantly lower number of good-quality embryos on day 3 in the G-TL group [50.7% (SD ± 30.6%) vs. 60.8% (SD ± 30.7%)]. Four out of the 11 measured morphokinetic parameters were statistically significantly different for the two media used. The mean levels of ammonium concentration in the media at the end of the culture period was statistically significantly lower in the G-TL group as compared with the G-2 group.

CONCLUSION(S)

We have shown that a single-step culture medium supports blastocyst development equivalently to established sequential media. The ammonium concentrations were lower in the single-step media, and the measured morphokinetic parameters were modified somewhat.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01939626.

Improved Oocyte Isolation and Embryonic Development of Outbred Deer Mice

In this study, we improved the protocol for isolating cumulus-oocyte complexes (COCs) from the outbred deer mice by using only one hormone (instead of the widely used combination of two hormones) with reduced dose. Moreover, we identified that significantly more metaphase II (MII) oocytes could be obtained by supplementing epidermal growth factor (EGF) and leukemia inhibition factor (LIF) into the previously established medium for in vitro maturation (IVM) of the COCs. Furthermore, we overcame the major challenge of two-cell block during embryonic development of deer mice after either in vitro fertilization (IVF) or parthenogenetic activation (PA) of the MII oocytes, by culturing the two-cell stage embryos on the feeder layer of inactivated mouse embryonic fibroblasts (MEFs) in the medium of mouse embryonic stem cells. Collectively, this work represents a major step forward in using deer mice as an outbred animal model for biomedical research on reproduction and early embryonic development.