A multi-center evaluation of a novel IVF cryostorage device in an active clinical setting.

The objective of this study was to evaluate the function, and usability of a novel automated software-guided cryostorage system in an active IVF laboratory setting. The investigational device (ID) was installed at 3 IVF laboratories (sites: α, ß, and γ). A total of 15 embryologists were trained to use the ID. Mock patient specimens containing mirrored live patient data were handled using the ID. Temperature readings were recorded every minute. Successful identification, storage, and retrieval of mock patient specimens by the ID were evaluated. To assess an LN2 pressure builder, the frequency of use and events of workflow interruption were logged. Student's t-test was used to determine statistical significance. The ID was in active use for 164 days total. During this time, 329 mock patient egg and embryo cohorts were handled by the ID. The mean ± SD temperatures during active use were: α, - 176.57 ± 1.83 °C; ß, - 178.21 ± 2.75 °C; γ, - 178.98 ± 1.74 and did not differ significantly. The highest recorded temperatures were: α, - 165.14 °C; ß, - 157.41 °C; γ, - 164.45 °C. A total of 1064 automation transactions on 409 specimen vessels were performed. Data was managed on 1501 eggs and embryos. The ID did not lose or misplace any specimen data or vessels, and no mock specimen was exposed to a detrimental (> - 150 °C) temperature excursion. Over the 25 LN2 pressure builder usages during 99 total days, there was 1 occurrence where usage interrupted workflow due to a lack of LN2 pressure. The ID has advantages over the current manual-based cryostorage systems, including radio frequency identification (RFID) tracking, automation of manual tasks, and software guidance to ensure accurate specimen storage and retrieval. The results of this study indicate that the ID can be integrated into active IVF laboratories.

Maternal physiology and blastocyst morphology are correlated with an inherent difference in peri-implantation human embryo development.

OBJECTIVE: To determine what patient and embryo characteristics are correlated with the developmental potential of the peri-implantation embryo. DESIGN: Retrospective study. SETTING: Research laboratory. PATIENTS: Six hundred fifty-one cryopreserved human blastocysts donated for research with informed patient consent. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Blastocyst attachment to fibronectin-coated plates, trophectoderm outgrowth area, epiblast cell number, total cell number, human chorionic gonadotropin secretion. RESULTS: Patients' body mass index, age, follicle-stimulating hormone: luteinizing hormone ratio on menstrual cycle day 3, antral follicle count on menstrual cycle day 3, antimüllerian hormone level on menstrual cycle day 3, and blastocyst morphological grade were correlated with peri-implantation development outcomes. After controlling for good-quality morphological grades, blastocysts from patients of advanced maternal age developed fewer epiblast cells than blastocysts from younger patients. CONCLUSIONS: Extended embryo culture during the peri-implantation period mirrors several disparities in fertility treatment outcome that we see clinically, including those from patients with advanced maternal age, high body mass index, and low ovarian reserve and from embryos with lower-quality morphological grades. This model system may be useful by providing an alternative or more sensitive endpoint assessment in studying patient, clinical, or laboratory factors that may influence preimplantation embryo developmental potential.

Fused blastocysts as a consequence of group embryo culture: observations, complications, and potential solutions.

How embryos are cultured, in groups or individually, can influence their development and have other unforeseen impacts on subsequent assisted reproductive technologies. Although a group culture of embryos improves the blastocyst formation rates, this can create conditions wherein separate blastocysts may fuse. This fusion of 2 blastocysts can create unique logistic issues for embryo biopsy and genetic analysis. New culture approaches have emerged to facilitate individual embryo culture without losing the benefit of the group culture approach. Unique culture dishes and adjustments of laboratory culture/embryo handling protocols offer possible solutions to minimize or avoid blastocyst fusion.

Comparison of electronic versus manual witnessing of procedures within the in vitro fertilization laboratory: impact on timing and efficiency.

OBJECTIVE: To evaluate the impact of an electronic witnessing system (EWS) on witnessing standard operating procedures and to assess embryologist perceptions of the EWS. DESIGN: Prospective cohort study. SETTING: Private in vitro fertilization laboratory network. PATIENTS: None. INTERVENTIONS: None. MAIN OUTCOME MEASURES: The time difference between manual and electronic double-witnessing procedures, and embryologist perceptions of the EWS. RESULTS: From 342 witnessing times analyzed (114 EWS, 114 manual, and 114 interruptions to witnesses), the EWS reduced mean (SD) total witnessing time (in seconds) by 91.5 (23.6) for intracytoplasmic sperm injection, 62.0 (17.9) for Day 3 embryo assessment, 58.3 (18.9) for fresh embryo transfer, and 59.4 (13.3) for frozen embryo transfer. This time reduction significantly decreased the overall time required for double-witnessing by 3.1- to 5.2-fold. A survey with 50 embryologists within the laboratory network indicated that most embryologists considered the EWS to improve sample traceability (78.3%), reduce errors in labeling issues (80.4%), and reduce the risk of sample mismatch errors by minimizing disruptions (60.9%). Furthermore, 82.6% thought that visual completion of the EWS dashboard provided peace of mind when leaving work and 84.8% were more confident knowing that all procedures were completed according to the EWS. CONCLUSIONS: An EWS can improve laboratory efficiency by significantly decreasing the time required for witnessing procedures and by minimizing interruptions. The EWS was well perceived by embryologists and laboratory managers and enhanced their confidence and peace of mind with regard to witnessing compliance and safety/accuracy.

Absence of SARS-CoV-2 (COVID-19 virus) within the IVF laboratory using strict patient screening and safety criteria.

RESEARCH QUESTION: Is there a risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral exposure and potential cross-contamination from follicular fluid, culture media and vitrification solution within the IVF laboratory using strict patient screening and safety measures? DESIGN: This was a prospective clinical study. All women undergoing transvaginal oocyte retrieval were required to have a negative SARS-CoV-2 RNA test 3-5 days prior to the procedure. Male partners were not tested. All cases used intracytoplasmic sperm injection (ICSI). The first tube of follicular fluid aspirated during oocyte retrieval, drops of media following removal of the embryos on day 5, and vitrification solution after blastocyst cryopreservation were analysed for SARS-CoV-2 RNA. RESULTS: In total, medium from 61 patients, vitrification solution from 200 patients and follicular fluid from 300 patients was analysed. All samples were negative for SARS-CoV-2 viral RNA. CONCLUSIONS: With stringent safety protocols in place, including testing of women and symptom-based screening of men, the presence of SARS-CoV-2 RNA was not detected in follicular fluid, medium or vitrification solution. This work demonstrates the possibility of implementing a rapid laboratory screening assay for SARS-CoV-2 and has implications for safe laboratory operations, including cryostorage recommendations.

Human eggs, zygotes, and embryos express the receptor angiotensin 1-converting enzyme 2 and transmembrane serine protease 2 protein necessary for severe acute respiratory syndrome coronavirus 2 infection.

OBJECTIVE: To study messenger ribonucleic acid (mRNA) and protein expressions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry receptors (angiotensin 1-converting enzyme 2 [ACE2] and CD147) and proteases (transmembrane serine protease 2 [TMPRSS2] and cathepsin L [CTSL]) in human oocytes, embryos, and cumulus (CCs) and granulosa cells (GCs). DESIGN: Research study. SETTING: Clinical in vitro fertilization (IVF) treatment center. PATIENTS: Patients undergoing IVF were treated at the Colorado Center for Reproductive Medicine. INTERVENTIONS: Oocytes (germinal vesicle and metaphase II [MII]) and embryos (1-cell [1C] and blastocyst [BL]) were donated for research at the disposition by the patients undergoing IVF. Follicular cells (CC and GC) were collected from women undergoing egg retrieval after ovarian stimulation without an ovulatory trigger for in vitro maturation/IVF treatment cycles. MAIN OUTCOME MEASURES: Presence or absence of ACE2, CD147, TMPRSS2, and CTSL mRNAs detected using quantitative reverse transcription polymerase chain reaction and proteins detected using capillary Western blotting in human oocytes, embryos, and ovarian follicular cells. RESULTS: The quantitative reverse transcription polymerase chain reaction analysis revealed high abundance of ACE2 gene transcripts in germinal vesicle and MII oocytes than in CC, GC, and BL. ACE2 protein was present only in the MII oocytes, and 1C and BL embryos, but other ACE2 protein variants were observed in all the samples. TMPRSS2 protein was present in all the samples, whereas mRNA was observed only in the BL stage. All the samples were positive for CD147 and CTSL mRNA expressions. However, CCs and GCs were the only samples that showed coexpression of both CD147 and CTSL proteins in low abundance. CONCLUSIONS: CCs and GCs are the least susceptible to SARS-CoV-2 infection because of lack of the required combination of receptors and proteases (ACE2/TMPRSS2 or CD147/CTSL) in high abundance. The coexpression of ACE2 and TMPRSS2 proteins in the MII oocytes, zygotes, and BLs demonstrated that these gametes and embryos have the cellular machinery required and, thus, are potentially susceptible to SARS-CoV-2 infection if exposed to the virus. However, we do not know whether the infection occurs in vivo or in vitro in an assisted reproductive technology setting yet.

Evaluation of the TMRW vapor phase cryostorage platform using reproductive specimens and in vitro extended human embryo culture.

OBJECTIVE: To assess the impact of shipment and storage of sperm, oocytes, and blastocysts in vapor phase nitrogen compared with static storage in liquid phase nitrogen. DESIGN: Prospective cohort-matched study. SETTING: Multiple in vitro fertilization laboratories in an in vitro fertilization network. PATIENT(S): Fifty-eight human embryos, 32 human oocytes, 15 units of bovine semen. INTERVENTION(S): Vapor vs. liquid nitrogen. MAIN OUTCOME MEASURE(S): The postwarming survival of oocytes, sperm, and blastocysts, and the developmental potential of blastocysts during in vitro extended culture. RESULT(S): Custom-designed labware, for use with the TMRW platform, enables continuous temperature monitoring during shipment and/or storage in the vapor phase robotic storage system. The highest temperature recorded for specimens shipped to a domestic laboratory was -180.2 °C with a mean ± SD of -190.4 ± 0.5 °C during shipment and -181.1 ± 0.6 °C during storage. Likewise, specimens shipped internationally had a high of -180.2 °C with a mean ± SD of -193.5 ± 0.6 °C during shipment and -181.2 ± 0.7 °C during storage. Results from the extended culture assays have revealed no deleterious effect of shipment and storage in nitrogen vapor. The viability of mammalian gametes and embryos was equivalent between the vapor phase and liquid phase storage. CONCLUSION(S): The evaluated system did not have any deleterious effects on the postwarming survival of sperm, oocytes, and blastocysts. The postwarming developmental potential of human blastocysts during in vitro extended culture was unaffected by storage and handling in the vapor phase nitrogen TMRW platform when compared with static liquid phase nitrogen storage. Our results suggest that the vapor phase cryostorage platform is a safe system to handle and store reproductive specimens for human assisted reproductive technology.

AI in the treatment of fertility: key considerations.

Artificial intelligence (AI) has been proposed as a potential tool to help address many of the existing problems related with empirical or subjective assessments of clinical and embryological decision points during the treatment of infertility. AI technologies are reviewed and potential areas of implementation of algorithms are discussed, highlighting the importance of following a proper path for the development and validation of algorithms, including regulatory requirements, and the need for ecosystems containing enough quality data to generate it. As evidenced by the consensus of a group of experts in fertility if properly developed, it is believed that AI algorithms may help practitioners from around the globe to standardize, automate, and improve IVF outcomes for the benefit of patients. Collaboration is required between AI developers and healthcare professionals to make this happen.

Performance of a deep learning based neural network in the selection of human blastocysts for implantation.

Deep learning in in vitro fertilization is currently being evaluated in the development of assistive tools for the determination of transfer order and implantation potential using time-lapse data collected through expensive imaging hardware. Assistive tools and algorithms that can work with static images, however, can help in improving the access to care by enabling their use with images acquired from traditional microscopes that are available to virtually all fertility centers. Here, we evaluated the use of a deep convolutional neural network (CNN), trained using single timepoint images of embryos collected at 113 hr post-insemination, in embryo selection amongst 97 clinical patient cohorts (742 embryos) and observed an accuracy of 90% in choosing the highest quality embryo available. Furthermore, a CNN trained to assess an embryo's implantation potential directly using a set of 97 euploid embryos capable of implantation outperformed 15 trained embryologists (75.26% vs. 67.35%, p<0.0001) from five different fertility centers.

Around one in seven couples have trouble conceiving, which means there is a high demand for solutions such as in vitro fertilization, also known as IVF. This process involves fertilizing and developing embryos in the laboratory and then selecting a few to implant into the womb of the patient. IVF, however, only has a 30% success rate, is expensive and can be both mentally and physically taxing for patients. Selecting the right embryos to implant is therefore extremely important, as this increases the chance of success, minimizes complications and ensures the baby will be healthy. Currently the tools available for making this decision are limited, highly subjective, time-consuming, and often extremely expensive. As a result, embryologists often rely on their experience and observational skills when choosing which embryos to implant, which can lead to a lot of variability. An automated system based on artificial intelligence (AI) could therefore improve IVF success rates by assisting embryologists with this decision and ensuring more consistent results. The AI system could learn how embryos develop over time and then uses this information to select the best embryos to implant from just a single image. This would offer a cheaper alternative to current analysis tools that are only available at the most expensive IVF clinics. Now, Bormann, Kanakasabapathy, Thirumalaraj et al. have developed an AI system for IVF based on thousands of images of embryos. Using individual images, the system selected embryos of a comparable quality to those selected by a human specialist. It also showed a greater ability to identify embryos that will lead to successful implantation. Indeed, the software outperformed 15 embryologists from five different centers across the United States in detecting which embryos were most likely to implant out of a group of high-quality embryos with few visible differences. Artificial intelligence has many potential applications to support expert clinical decision-making. Systems like these could improve success, reduce errors and lead to faster, cheaper and more accessible results. Beyond immediate IVF applications, this system could also be used in research and industry to help understand differences in embryo quality.

Impact of a controlled culture temperature gradient on mouse embryo development and morphokinetics.

RESEARCH QUESTION: Temperature control within the IVF laboratory is an important aspect of a quality control system, helping to reduce environmental stress and ensure good-quality embryo development. Temperature fluctuations are probably more common than expected and the optimal temperature for embryo culture is not known. Modern incubators offer the opportunity to examine the impact of culture temperature on preimplantation embryo development while controlling for other variables within the system. The purpose of this study was to examine the effect of a range of temperatures during extended embryo culture on resulting mouse embryo development and morphokinetic timings. METHODS: Using a single time-lapse incubator with six individual chambers, frozen-thawed one-cell mouse embryos were cultured individually at temperatures adjusted by 0.5°C between chambers to cover the range of 35.0-37.5°C. Resulting blastocyst formation and embryo morphokinetic timings were recorded and compared. RESULTS: Changes in culture temperature had a significant impact on mouse blastocyst development and morphokinetic timings (P < 0.05). Under the conditions used in this study, blastocyst development was best at 37.0°C. Mouse preimplantation embryo mitotic cell divisions were generally slower at cooler temperatures and accelerated as the temperature increased from 35.0°C to 37.5°C. CONCLUSION: Incubator culture temperature must be carefully controlled, as even slight variations of 0.5°C in the temperature used for extended embryo culture can have significant impacts on embryo development and mitotic cell divisions. These data have potential implications for application of universal morphokinetic selection algorithms and may help explain differences in mitotic errors/embryo mosaicism between laboratories.

Controversies in ART: can the IVF laboratory influence preimplantation embryo aneuploidy?

Published reports have indicated that rates of preimplantation embryo aneuploidy in a control donor population may vary between IVF centres. This suggests that location-specific conditions, in the clinic, IVF or genetics laboratory, may be influencing the chromosome dynamics or diagnosis. More recent reports suggest that rates of embryo mosaicism, representing mitotic errors, may vary between IVF centres. This would suggest perhaps a laboratory-controlled variable is influencing mitotic cell division during preimplantation embryo development. Various IVF laboratory-controlled factors may be impacting chromosome separation and segregation. Variables including type of culture media, pH, temperature, osmolality and oxygen concentration could all be possible factors influencing embryo aneuploidy. Furthermore, laboratory techniques, method of insemination, laser use or handling of biopsied cells may also influence genetic results. These IVF laboratory variables will be reviewed and literature suggesting a possible link to mitotic aneuploidy/mosaicism discussed.

Controversies in ART: considerations and risks for uninterrupted embryo culture.

With new time-lapse incubators, IVF laboratories have increased use of single step media, often used in an uninterrupted approach. This simplifies the culture process for embryologists, may help reduce costs, offers the potential to reduce cell handling and associated harmful environmental stressors, and improves embryo quality and outcomes. One could argue, however, that optimized quality control and culture conditions are required to implement uninterrupted culture successfully. Without impeccable laboratory conditions and oversight, while trying to reduce harmful environmental stress, the laboratory could be imparting stress. Factors such as medium evaporation and associated osmolality and pH increases, as well as volatile organic compound accumulation, could offset any advantage of reduced dish or embryo handling. When implementing uninterrupted embryo culture, attention must be paid to incubator humidity, amount, quality and type of oil used, medium formulation and protein quality, as well as laboratory air and gas supply quality, and volatile organic compound content.

Forty years of IVF.

This monograph, written by the pioneers of IVF and reproductive medicine, celebrates the history, achievements, and medical advancements made over the last 40 years in this rapidly growing field.

The why, the how and the when of PGS 2.0: current practices and expert opinions of fertility specialists, molecular biologists, and embryologists.

STUDY QUESTION: We wanted to probe the opinions and current practices on preimplantation genetic screening (PGS), and more specifically on PGS in its newest form: PGS 2.0? STUDY FINDING: Consensus is lacking on which patient groups, if any at all, can benefit from PGS 2.0 and, a fortiori, whether all IVF patients should be offered PGS. WHAT IS KNOWN ALREADY: It is clear from all experts that PGS 2.0 can be defined as biopsy at the blastocyst stage followed by comprehensive chromosome screening and possibly combined with vitrification. Most agree that mosaicism is less of an issue at the blastocyst stage than at the cleavage stage but whether mosaicism is no issue at all at the blastocyst stage is currently called into question. STUDY DESIGN, SAMPLES/MATERIALS, METHODS: A questionnaire was developed on the three major aspects of PGS 2.0: the Why, with general questions such as PGS 2.0 indications; the How, specifically on genetic analysis methods; the When, on the ideal method and timing of embryo biopsy. Thirty-five colleagues have been selected to address these questions on the basis of their experience with PGS, and demonstrated by peer-reviewed publications, presentations at meetings and participation in the discussion. The first group of experts who were asked about 'The Why' comprised fertility experts, the second group of molecular biologists were asked about 'The How' and the third group of embryologists were asked about 'The When'. Furthermore, the geographical distribution of the experts has been taken into account. Thirty have filled in the questionnaire as well as actively participated in the redaction of the current paper. MAIN RESULTS AND THE ROLE OF CHANCE: The 30 participants were from Europe (Belgium, Germany, Greece, Italy, Netherlands, Spain, UK) and the USA. Array comparative genome hybridization is the most widely used method amongst the participants, but it is slowly being replaced by massive parallel sequencing. Most participants offering PGS 2.0 to their patients prefer blastocyst biopsy. The high efficiency of vitrification of blastocysts has added a layer of complexity to the discussion, and it is not clear whether PGS in combination with vitrification, PGS alone, or vitrification alone, followed by serial thawing and eSET will be the favoured approach. The opinions range from in favour of the introduction of PGS 2.0 for all IVF patients, over the proposal to use PGS as a tool to rank embryos according to their implantation potential, to scepticism towards PGS pending a positive outcome of robust, reliable and large-scale RCTs in distinct patient groups. LIMITATIONS, REASONS FOR CAUTION: Care was taken to obtain a wide spectrum of views from carefully chosen experts. However, not all invited experts agreed to participate, which explains a lack of geographical coverage in some areas, for example China. This paper is a collation of current practices and opinions, and it was outside the scope of this study to bring a scientific, once-and-for-all solution to the ongoing debate. WIDER IMPLICATIONS OF THE FINDINGS: This paper is unique in that it brings together opinions on PGS 2.0 from all different perspectives and gives an overview of currently applied technologies as well as potential future developments. It will be a useful reference for fertility specialists with an expertise outside reproductive genetics. LARGE SCALE DATA: none. STUDY FUNDING AND COMPETING INTERESTS: No specific funding was obtained to conduct this questionnaire.

Live-cell quantification and comparison of mammalian oocyte cytosolic lipid content between species, during development, and in relation to body composition using nonlinear vibrational microscopy.

Cytosolic lipids participate in the growth, development, and overall health of mammalian oocytes including many roles in cellular homeostasis. Significant emphasis has been placed on the study of lipids as a dynamic organelle, which in turn requires the development of tools and techniques to quantitate and compare how lipid content relates to cellular structure, function, and normalcy. Objectives of this study were to determine if nonlinear vibrational microscopy (e.g., coherent anti-Stokes Raman scattering or CARS microscopy) could be used for live-cell imaging to quantify and compare lipid content in mammalian oocytes during development and in relation to body composition; and compare its efficacy to methods involving cellular fixation and staining protocols. Results of this study demonstrate that CARS is able to identify lipids in live mammalian oocytes, and there exists quantifiable and consistent differences in percent lipid composition across ooctyes of different species, developmental stages, and in relation to body composition. Such a method of live-cell lipid quantification has (i) experimental power in basic cell biology, (ii) practical utility for identifying developmental predictive biomarkers while advancing biology-based oocyte/embryo selection, and (iii) ability to yield rationally supporting technology for decision-making in rodents, domestic species, and human assisted reproduction and/or fertility preservation.

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.

Antimüllerian hormone as a predictor of good-quality supernumerary blastocyst cryopreservation among women with levels <1 ng/mL versus 1-4 ng/mL.

OBJECTIVE: To determine whether antimüllerian hormone (AMH) levels predict the availability of good-quality supernumerary blastocysts for cryopreservation. DESIGN: Retrospective study. SETTING: Two fertility centers. PATIENT(S): First fresh IVF cycles (n = 247) grouped as follows: 40 women <35 year old with AMH <1 ng/mL and 77 women with AMH 1-4 ng/mL; 62 women ≥35 year old with AMH <1 ng/mL, and 68 women with AMH 1-4 ng/mL. INTERVENTION(S): AMH level measured before IVF with ovarian stimulation protocols based on patient age and AMH level, including short gonadotropin-releasing hormone (GnRH) agonist, GnRH antagonist, or GnRH agonist microdose flare; supernumerary good-quality blastocysts cryopreserved on days 5 or 6 after retrieval. MAIN OUTCOME MEASURES(S): Supernumerary good-quality blastocysts for cryopreservation in relation to AMH levels. RESULT(S): Among women <35 years of age, there was a statistically significant difference in the number of patients with supernumerary good-quality blastocysts for cryopreservation between the groups with AMH <1 ng/mL and AMH 1-4 ng/mL (30.0% vs. 58.4%) when adjusted for age. Among women ≥35 years of age, there was a statistically significant difference in the number of patients with supernumerary good-quality blastocyst cryopreservation between groups with AMH <1 ng/mL and AMH 1-4 ng/mL (16.1% vs. 42.6%), when adjusted for age. CONCLUSION(S): Low AMH levels are associated with a statistically significantly lower likelihood of blastocysts for cryopreservation as compared with higher AMH levels. This effect was seen among women both <35 and ≥35 years of age. Patient counseling should include realistic expectations for the probability of good-quality supernumerary blastocysts available for cryopreservation.

Optimal human embryo culture.

A large contributor to success during in vitro fertilization (IVF) lies in the processes occurring within the IVF laboratory. These processes make up the "culture system." This system entails numerous procedures and technical steps that must be optimized to produce a competent embryo. Notably, variations exist between programs that include differences in patient population, clinical stimulation, and other factors. Thus, a single "optimal" culture system to be utilized between all laboratories is likely not feasible. Rather, laboratory procedures should be optimized based on an individual laboratory's performance. That being said, within the scientific literature, there are key components, approaches, and techniques within the culture system that have been shown to be superior to alternatives. These key components important in improving embryo culture are discussed.