Early embryo development: the current perspective in molecular evaluation and clinical status

Early embryo development and competence mechanisms are paramount to ART's success but are still underexplored in human-relevant animal models. Clinical embryo evaluation remains largely based on subjectively evaluated morphological characteristics. In the current era of biomarkers and low-input high-throughput technologies, it is possible to investigate the multi-complex molecular landscape of the embryo during development from the zygote up to the blastocyst stage. The scope of this article is to review the underlying molecular mechanisms of pre-implantation embryo development. In addition, we briefly explore the latest advances in embryo quality assessment - including molecular and epigenetic evaluation and technical advances such as time-lapse imaging and artificial intelligence - together with clinical challenges for selecting the best embryo for single embryo transfer.