Metabolism of human embryos following cryopreservation: implications for the safety and selection of embryos for transfer in clinical IVF.

BACKGROUND Cryopreservation of supernumerary embryos is routinely performed in human-assisted reproduction, providing a source of embryos which can be thawed for use in subsequent treatment cycles. However, the viability of cryopreserved embryos has traditionally relied on morphological assessment, which is a poor predictor of embryo health since freezing leads to a significant overall reduction in implantation potential, and its long-term efficacy is unknown. This study describes how the post-thaw metabolism of human embryos can be used to predict future development to the blastocyst stage. METHODS HPLC was used to analyse the post-thaw amino acid metabolism of human embryos from day 2 to day 3 of development. RESULTS It was possible to predict with 87% accuracy which frozen-thawed embryo would develop to the blastocyst stage. Developmentally competent embryos were more metabolically quiescent than their arresting counterparts. Amino acid turnover was also capable of distinguishing between the developmental potential of the best, Grade I embryos P < 0.05. CONCLUSIONS The data suggests that cryopreservation in IVF is a safe procedure and that amino acid turnover can be used to select which cryopreserved embryo will develop to the blastocyst stage, irrespective of their post-thaw grade.