Glucose metabolism of human morula and blastocyst-stage embryos and its relationship to viability after transfer.

The pregnancy rate and implantation rate following blastocyst transfer in the human have been reported to be high; however, it has remained necessary to transfer 2-3 blastocysts to achieve these rates. Morphological criteria are currently used to select blastocysts for transfer and have some limited correlation with ongoing viability. Glucose metabolism of 189 human morula to blastocyst stage embryos was analysed using a non-invasive ultramicrofluorescence technique to determine if this could be used to predict viability. There was a linear trend to increased glucose uptake with progression from the morula to the hatching/hatched blastocyst stage of development, whereas glycolytic activity did not vary. There was no consistent difference in glucose uptake or glycolytic activity for embryos at the various morphological stages on day 5 compared to day 6 in vitro. Glucose uptake and glycolytic activity of the nine embryos positively identified as having implanted following transfer varied and were apparently not different from the values for embryos that failed to implant. In addition, viability was demonstrated to be compatible with high glycolytic activity, with four of nine implanted embryos having a glycolytic activity in the highest 15% of the population of embryos studied. Glucose uptake and glycolytic activity of male and female embryos did not appear to be different. Glucose metabolism cannot be used prospectively to select viable human morula or blastocyst stage embryos for transfer and it is also unlikely to be a useful tool to predict the sex of the embryo.