Embryo viability and metabolism: obeying the quiet rules.

BACKGROUND It has been proposed that preimplantation embryo viability during culture and following embryo transfer is associated with a 'quiet' metabolism. Viable embryos may be better equipped to contend with damage to the genome, transcriptome and proteome, or they may possess less damage than non-viable embryos. METHODS Much of the data for the quiet embryo hypothesis was obtained in the human and mouse. In this article, evidence is reviewed suggesting that the quiet hypothesis may equally be applied to reproduction in livestock, which can provide good models for the human. RESULTS Data, particularly for the sheep and cow, suggest that a quiet metabolism during early embryo development is consistent with successful embryo development. Conversely, an 'active' metabolism is associated with sub-optimal outcomes in later life. CONCLUSIONS The challenge is to identify the range of values for a given marker within which an embryo has a high chance of giving rise to healthy offspring. We also speculate on the ways in which such a metabolic profile might be encouraged and the implications for weight loss in obese women prior to conception.