Embryo Culture From Media to Epigenetics
Many reports have been written on conditions and media for embryo culture in the laboratory. This is because the subject is complex and multifaceted, which reflects the variations in practice. This scoping review focuses on the topic of culture media conditions and the practices that underpin them. It aims to present the perspectives of practitioners and highlight the important points, debates and controversy while addressing the concerns of practicing embryologists.
Numerous studies have suggested that in vitro fertilization (IVF), cycles may influence the implantation and pregnancy rates by influencing embryo quality. This hypothesis is supported by more evidence. The connection between IVF outcomes and medium composition is still being investigated (4-8). The evolution of embryo-culture systems is a major reason IVF results have improved over the past decade.
Studies on mammals over the past 50 years have made a tremendous contribution. The original goal of defining the ideal embryo culture medium was to replicate the tubal fluid’s composition . Since then, we have made great strides in determining the exact metabolic requirements and the effect of the medium on gene expression from the blastocyst to the oocyte. Media are designed using animal models as a basis. This has led to questions about the media’s effect on human embryology The performance of mouse embryos is the basis for commercially available media . Human embryos can survive in vivo and adapt to the various conditions that the mother provides during gestation . There is a lot of variation in commercial media for human embryo use. It is easy to see why the perfect culture media composition that mirrors the in vivo exposures and support is not yet possible.
Although media were initially made in-house, there was limited quality control. Now, they are widely available commercially. They contain nutrients, vitamins, growth factors, and are strictly manufactured by companies that adhere to strict quality standards . While embryologists have long used commercially available media, there are some advantages to producing your own synthetic sequential media. It is possible to conduct a quality control that is accurate and allows the laboratory to follow a specific protocol. It is possible to add or remove specific components. Finally, IVF programs are completely independent and can accommodate unexpected circumstances such as an increase in IVF patients. The issue of variation among different batches is also important .
Although there has been a long-running debate about whether to use commercial media or in-house-produced sequential media, the reality is that the dilemma has been solved in favor of single-media commercially produced continuously. However, it appears that there are still some advantages to the synthetic in-house option. Yoon and colleagues. Yoon et al. found no difference in implantation rates, pregnancy rates or the percentage of cycles with cryopreservation between the in-house and commercially available sequential media. The practicalities of producing in-house sequential media are still a problem. Therefore, it is not realistic for IVF labs to invest in in-house media.
In recent years, embryologists have been challenged by the question of single-step or sequential medium culture. However, there is no solid evidence to support either choice. Every laboratory should choose the one that suits its needs. A sequential system uses one type of medium until development day 3. Then, a new medium is used to replace the old medium until days 5-6. The single culture system, on the other hand, only requires one type of medium for the entire process. This is thought to be beneficial because it allows embryos the ability to control their own microenvironment and simultaneously reduces work by eliminating an additional step in the culture process. It is possible to accommodate a single medium culture by renewing the media on day 3. One-step media is the most common method of IVF. There is a tendency to go back to the original idea in improved continuous culture media. There are still opposing arguments. However, the full understanding of the metabolic profile and needs of the human embryo is an ongoing process. The answers that define the synthesis of commercial media come from non-human embryo cultures.
Most media manufactured by manufacturers are CE (European Conformity), and MEA (Mouse Embryo Assay). The CE marking entails full disclosure of the medium’s exact composition, a quality assessment, post-market surveillance, systems to report and examine adverse incidents and traceability . MEA marking, on the other hand, is indicative that >=80% of mouse embryos have been successfully tested. However, it has been widely criticised as it only confirms toxicity and not compatibility with human embryos. The actual number of embryos tested is not reported, which could raise questions about the validity of the reported results. A certificate of analysis for each batch of culture medium is available upon request. It can also be found online. Despite this, even for the most basic aspects of embryo culture protocols and practices, companies are not able to agree on which practice is best. Vajta et.al.. This could be a problem for IVF lab practice. This could mean that the culture does not rely solely on media from one company, but instead uses media from multiple companies. This is a common practice, especially when it comes to different stages of the culture.
