I-11: The Use of Oxygen Consumption for Oocyte and Embryo Selection

Assisted human reproduction is characterized by a high variability in results regarding pregnancy and birth rates. In fact, in a cohort of fertilized oocytes from the same stimulation cycle, the development rate varies drastically, even though produced at the same time and under similar conditions. This variability results in large differences in implantation potential of human embryos developed in vitro, despite similarities in observable parameters such as embryo development rates and morphology. There is no doubt that embryo morphology (determined by the number, size, and shape of blastomeres, the proportion of fragments, and the presence of multinucleated blastomeres) has some predictive value on development and implantation potential. Some noninvasive methods such as metabolomic profiling are still at initial stages of development, awaiting their verification in daily laboratory practice, but it could be applied in the future with further improvements. One of these noninvasive methods ,which is consolidating at the moment as a good indicator of overall metabolic activity and a valuable parameter for evaluating embryo quality is the O2 consumption (OC), which is directly related with the capacity of an embryo to produce ATP via oxidative phosphorylation, a process that utilizes 30% and 60-70% of the oxygen consumed by the embryo at the early cleavage and blastocyst stages respectively. The purpose of this presentation is to describe new and potentially useful aspects of oxygen consumption as a tentative method for embryo selection. We evaluated the influence of different stimulation protocols on the oocyte O2 consumption as well as the influence of different oocyte dimorphisms in respiration rates. The next step was to study how the fertilization process might be affected by the oxygen uptake. In the second part of the presentation we have focused our attention on embryos, measuring the OC during 3 days of culture until embryo transfer and evaluating its correlation with embryo development and reproductive outcome.