Embryo oxygen consumption to evaluate the embryo quality

Early prediction of the viability and quality of in vitro developed embryo is still challenging. After that, various kinds of evaluation methods for embryo such as morphological analysis, proteomics, and metabolomics were reported. Time lapse system is also a good option to know the embryo quality. However, more objective method for the embryo evaluation is needed. To evaluate oxygen consumption, that is embryo respiration, is less invasive and possible to evaluate embryo viability and quality. It is reported that the bovine embryos with higher oxygen consumption were better candidates to further development into good quality embryo and yielded higher pregnancy rate after embryo transfer. Oxygen consumption is an ideal indicator of overall metabolic activity because ATP is generated predominantly by oxidative phosphorylation. Cell respiratory assay system (CRAS) is a technique in which the tip of a microelectrode monitors the local distribution of oxygen near embryo. The objective of this study is to clarify whether embryo respiration reflect the quality of the embryo or not. A prospective study. Sixty-nine normal fertilized frozen-thawed 2 pronucleus stage embryos from 11 patients, all of them had successfully conceived by IVF and delivered, had enrolled in this study. All study subjects had signed informed consents prior to entering the study, in accordance to local IRB protocol. Oxygen consumption of each embryo was evaluated by cell respiratory assay system every day for 6 days. Embryo morphology was also evaluated every day for 6 days. Oxygen consumption of the morphologically good quality embryo at day 4 and day 5 was significantly higher than that of the morphologically poor quality embryo (p<0.05 and p<0.01, respectively). Moreover, oxygen consumption of the morphologically poor quality embryo decreased on day 4. However, no decrease was observed for the morphologically good quality embryo. So, it was possible to classify the morphologically good and poor quality embryo by setting the cutoff value of the embryo oxygen consumption to 4.93 x 1015/mol s-1. Further analysis of oxygen consumption of the embryo that later had become good quality blstocyst, appropriate oxygen consumption on day 3 embryo was 4.80-7.18 x 1015/mol s-1. Good quality blastocyst rate in good quality embryo on day 2 and appropriate oxygen consumption (4.80-7.18 x 1015/mol s-1) on day 3 was 46.2% (12/26) and it was significantly higher than others (2.7% (1/37), p<0.01). Moreover, there was a significant positive correlation between blastocyst quality score and oxygen consumption of the embryo (r2=0.583, p<0.01). Embryo morphological analysis on day 2 and the investigation of day 3 or day 4 oxygen consumption of the embryo become good predictor to detect the good quality blastocyst.