Pursuit of Markers to Assess and Select Competence of invitro-Produced Embryos

Morphological classification has been used as a conventional and noninvasive method to select pre-implantation embryos for transferring to recipients. However, low implantation rate and embryonic mortality after embryo transfer, specially using invitro produced or manipulated embryos, indicate than this method is not reliable enough to reflect the developmental competence of an embryo and it needs to be improved for biological and applied needs. In fact, embryo viability and competence correlate better with gene expression pattern than with embryo morphology. Nevertheless, the analysis of gene expression in pre-implantation embryos is an invasive procedure that most frequently implies the lysis of the embryo or a part of it. In this context, the identification of secreted markers linked to embryo quality and development competence may be a useful tool to classify pre-implantation embryos. Candidates may be studied in order to define suitable markers for embryo selection, widely expressed across species and correlated to developmental capacity and survival up to term. This paper presents a review of the literature on the different methods that may be used for embryo scoring as well of those used to predict embryo competence and quality. The most practical methods are those that consider embryo morphology. However, it seems that the molecular signature of each individual embryo is more predictive of its competence and capability to produce a healthy offspring. Many studies and experiments are required to propose a consistent method for embryo selection applicable in the assisted reproductive technologies in both humans and animals.