Assessment of embryo potential by visual and metabolic evaluation

Morphological evaluation of embryos is essential to the success of embryo transfer procedures and is presumed to reflect embryo metabolic activity. To investigate this assumption, correlations between morphological and metabolic parameters were determined for cultured murine morulae. After 18 h (n = 47) or 36 h (n = 48) of culture in M16, the developmental rate and quality (poor or good) of embryos were estimated, and, then, either their (14)C-glucose utilization or (35)s-methionine uptake and incorporation were measured. Retarded developing, or poor-quality embryos had lower mean glucose utilization, uptake and incorporation rates than normally developing or good-quality embryos (P < 0.05). After 18 h of culture, an association was found between developmental rate and metabolic activity, but this was not evident after 36 h of culture. Similarly, an association was found between embryo quality and metabolic activity. As expected, poor embryo quality was indicative of low metabolism throughout the culture period, but good quality did not necessarily indicate normal metabolic activity. Thus, morphological parameters do not always reflect metabolic competence, and some functional defects were not detectable by visual evaluation alone. Measuring metabolic parameters could complement visual evaluation for a better selection of embryos prior to transfer.