Selection of viable mouse blastocysts prior to transfer using a metabolic criterion.

The success rate of human in-vitro fertilization (IVF) remains low, with only approximately 10% of embryos transferred resulting in a term pregnancy. A major contributor to this embryonic loss is poor embryo development in vitro. Such poor development can be attributed to both chromosomal and anatomic anomalies in oocytes after ovarian stimulation and to suboptimal embryo culture conditions. The low success rate of IVF is compounded by an inability to select those embryos most likely to implant after transfer (viable). Currently morphology is used almost exclusively as the sole criterion to decide which embryos are replaced. This procedure is not only subjective but has a poor correlation with subsequent developmental competence. Therefore, the development of techniques to quantify embryo viability prior to transfer will significantly increase pregnancy rates. We report here that the non-invasive assessment of glycolytic activity (percentage of glucose converted to lactate) in individual mouse blastocysts prior to transfer can be used successfully to identify viable embryos. Blastocysts with a low glycolytic activity, close to that of in-vivo developed blastocysts, had a significantly higher viability than those with abnormally elevated levels of glycolysis. Using glycolytic activity as a marker of viability resulted in a four fold increase in the pregnancy rate compared with embryos selected at random for transfer. We propose that the success of clinical IVF can be increased significantly by employing quantitative tests for viability.