Non-invasive biomarkers of embryo quality: how they can contribute to the success of Assisted Reproduction Techniques

Since the beginning of human IVF, various grading systems based on numerous characteristics that can be observed in pre-implantation embryos have been evolved, with the aim of quantitating embryo development, viability and implantation potential. The advantages of static morphological assessment are the simplicity and the limited expenses related to the method; there are, however, several limitations as it doesn’t allow to evaluate events that occur during in vitro development which are fundamental for determining embryo quality. The introduction of Time Lapse Microscopy in the field of Assisted Reproduction allowed the identification of parameters that may non-invasively predict the developmental potential of a cleavage-stage embryo through continuous monitoring; the capture of images of the embryos developing in vitro at regular intervals throughout the culture period, in fact, provides embryologists with a more sophisticated and promising tool for the study and selection of the human preimplantation embryo. However, to date, and despite significant research effort, no single reliable biomarker with a sufficiently high predictability of live birth has yet been identified. Consequently, the search for biomarkers must no longer occur in isolation and the combination of TLT with other markers of embryo physiology is a natural evolution of both fields. In recent years, new methods have been developed involving the analysis of embryo physiology to determine viability. The use of metabolomic and proteomic platforms has yet to be proven and employed clinically, and hence such approaches could ultimately assist in defining parameters that can be used in embryo selection. An example of a non-invasive assessment of embryo quality can be represented by the analysis of EVs in the spent culture media; extracellular vesicles, in fact, can be nowadays studied as biomarkers for several reproductive conditions. The proposal of this thesis was to evaluate how the morphokinetic assessment of embryo development can contribute to the success of Assisted Reproduction treatments. Data obtained through the record of cellular divisions parameters of embryos incubated in a time lapse system, were retrospectively analyzed according to different outcomes of IVF treatments in order to identify markers that can provide more information on embryonic quality and, consequently, can guide the embryologist in the selection of embryos with the greatest development and implantation potential in a non-invasive way. At the same time, a preliminary analysis was started on the spent culture media of the embryos cultured in vitro with the aim of evaluating the presence and quantity of extracellular vesicles (EVs) that can be considered non-invasive biomarkers able to provide additional information on embryo quality.