Traditionally, approximations for identifying the best embryos prior to transfer were essentially based on a morphological evaluation; obviously, these observations provided indications which supported the skill of the embryologist when it came to selecting an embryo for transfer.
The definition of what represents a “perfect embryo” and the choice of those with the best potential for implantation are still very imprecise concepts, and the ability (or lack of ability) to estimate embryo competence correctly has become a critical point of the process. As a result, the selection options and strategies used will depend on all of the information that we can find out about the embryo.
The morphological and growth criteria which are currently used for evaluating embryo viability on day 3 either underestimate or overestimate their potential for development. In light of the uncertainty associated with the morphological examination on day 3, some reproduction centres have opted for a longer cultivation period for evaluating embryo competence. While the morphological examination method has the advantage of being simple, non-invasive and quick, it has the disadvantage of being highly subjective and requiring specialised training and a certain degree of experience, and there is little hope for its standardisation.