Selecting the best embryo to transfer to the uterus is key to successful in vitro fertilization (IVF). A huge amount of research has been devoted to this topic and there are numerous methods used, from simple morphological assessment to molecular biological techniques to assess the genome and metabolism of the newly fertilized embryo. For many of these techniques, an adequate evidence base is lacking, and expert opinion is valuable. Clinical imperatives require ranking all embryos in a cohort according to their viability, thereby enabling the selection of the best embryo to optimize live...