ASSESSMENT OF PREIMPLANTATION EMBRYO DEVE LOPMENT - EXPERIMENTAL-DATAIN MAMMALS

Assessing and/or improving the implantation prognostic remain a major goal for research studies as well as for teams doing embryo transfer i n many species. Criteria for such a goal were focussed ten years ago a nd combined theoretically: -sensitivity for applying to one embryo; -c lear cut-off for individual decision; -fastness to be suitable for emb ryo transfer in due time; -no toxicity or invasiveness for embryo; -fi nally some simple technical approach in order to be applies by a large number of teams. Moreover whatever may be qualitative or quantitative criteria, they should be relied to the final result as alive newborn. The more ancient way to appreciate embryo quality deal with the simpl e observation of morphological and kinetic criteria about embryo, but such non invasive approach was obviously limited, in spite of the posi tive influence of regular blastomers, absence of fragmentation and syn chronization with time of transfer on implantation rate. The major tra nscriptionnal activity of human embryo developping between 6 and 8 cel ls stage, of course, were unassessed by transfer to day 2. Moreover th e apparent quality of the embryo better reflected oocyte qualify than embryo quality. Coculture development encompassed only partially such limitation. Using fluorescent probes, it was possible to evaluate some metabolic activity as well as membrane integrity, but such criteria r evealed to be both invasive and uneasily reliable with develomental ab ility of the embryo. Methods dealing with glucidic, protidic or lipidi c metabolisms are developped elsewhere, but revealed uneasy to apply, due both to their invasiveness or technical difficulties and their lar ge inter-individual variability Some hope has raised by the finding of growth factors or cytokines which are expressed by the embryo and/or embryotrophic but a lot of works remain to be down before an easy prac tical application.