The Future of Human Embryo Culture Media – Or Have We Reached the Ceiling
The fundamental goal/role of the laboratory and, therefore, the culture media has been to maintain the inherent viability of the gametes/embryos before replacement to the mother. Over the last 10-15 years, there have been significant advancements in this area, with culture media developing from simple salt solutions into highly complex defined media, specifically designed to reduce stress to the embryo and maintain high pregnancy rates. As a direct result of the Blastocyst Test in Delhi, its advancements in culture media formulation, and increased awareness of the contribution of QA/QC, single embryo transfer is now a realistic outcome for most patients. Although the role of culture media in stress reduction and viability maintenance may have reached its ceiling, with likely only incremental increases in pregnancy rates to be made in the future, there may be a new role for culture media as a therapeutic device evolving from the goal of maintaining the inherent viability to improving the viability of the gametes and embryos.
Pre-compaction stage embryo
Initially, the oocyte and early embryo are relatively quiescent cells reflecting the fact that the egg has sat dormant in the ovary for many years. Each cell undergoes a series of reductive mitotic divisions called ‘cleavage,’ during which the embryo’s total size does not change. So with each division, the size of the cells, or blastomeres, is reduced, which assists in restoring the exaggerated cytoplasmic: nuclear ratio back to levels more traditionally observed in somatic cells.
Following the cleavage stages, the pre-implantation embryo changes morphology by compacting and forming a morula, at which stage the human source has reached the cornea of the uterus. Compaction typically occurs between the 8 and 12 cell stages in the human and involves the blastomeres flattening into one another to maximize cell-cell contact, resulting in the polarisation of the cells.
Due to the high energy requirements at these later stages, the embryo now readily consumes glucose in a balance with cytoplasmic and mitochondrial metabolism. The metabolic quotient in the blastocyst reflects that commonly seen in highly proliferating tissues. The embryo resides in the uterus at this stage, and the vastly different environment mirrors the difference in the source itself that the uterus provides in comparison to the oviduct with high levels of glucose and both non-essential essential amino acids and lower levels of lactate and pyruvate.
Blastocyst Culture and Transfer treatment in Delhi
Preimplantation embryo culture: the past
The ability to culture tissue samples was pioneered in the early 1900s, and during this time, the importance of using biologically defined media was acknowledged. A biologically determined medium was beneficial because it could be reproduced at different times and in other laboratories. It can also be varied in a controlled manner and is free of enzyme activities that may interfere with the responses being studied (Biggers 1971). The design of chemically defined media accelerated in the 1940s, as media was designed to support the growth of plant and animal cells.
Human embryo culture: the present
The first 20-25 years of human IVF treatments were almost exclusively resulting from the culture of embryos today two or, in some cases, day three before transfer to the uterus. The human and primate are the only two species where the source has the plasticity required for this asynchronous transfer. However, this early transfer to the uterus was necessitated by an inability to grow the human embryo in culture beyond these stages at high rates.
Culture media components
To understand the different cultural media available for use on the human embryo, it is essential to understand the literature behind each of the critical components in the formulation. The significance of this is becoming more apparent with the recent publication that different culture media may program the human embryo such that birthweight parameters are altered. Therefore, there is an increasing imperative to understand the components of the culture media and how they interact with the developing embryo.
The future of human culture media: from maintenance to rescue and blastocyst test in Delhi
To date, the laboratory’s philosophy and, therefore, the function of the culture medium has been in maintaining the inherent viability of the gamete/embryo until they are returned to the female reproductive tract. This philosophy has worked well such that results from around the world indicate that more than 85% of women under the age of 35 should expect to conceive with a single embryo transfer within 12-18 months of IVF treatment. It is therefore likely that, in these patient groups where there are healthy gametes with high inherent viability, the culture media that we currently use functions at a suitable level, providing maximal outcomes for these patients.