Comparison of 2, 5, and 20 % O2 on the development of post-thaw human embryos

The objective of this study is to investigate the effect of 2, 5, and 20 % O-2 on post-thaw day 3 human embryo culture until blastocyst stage. One hundred fifty-five day 3 human embryos were used. One hundred twenty out of 155 embryos were recovered after thawing. Surviving embryos were distributed into 2, 5, or 20 % O-2 groups and cultured for 2.5 days. At the end of culture, blastocyst formation was assessed, and then, embryos were collected for RT-qPCR or immunofluorescence analysis. Using visible blastocoel to define blastocyst formation, 58.7 % (27/46) of surviving day 3 embryos formed blastocyst at 2 % O-2, 63.6 % (28/44) at 5 % O-2, and 66.7 % (20/30) at 20 % O-2. The difference in blastocyst formation rates was not significant. Average blastocyst cell number was 119.44 +/- 11.64 at 2 % O-2, 142.55 +/- 22.47 at 5 % O-2, and 97.29 +/- 14.87 at 20 % O-2. Average apoptotic rate was 4.7 % +/- 0.4 % for blastocyst formed at 2 % O-2, 3.5 % +/- 0.7 % at 5 % O-2, and 5.8 % +/- 1.1 % at 20 % O-2. Apoptosis rate was significantly lower for blastocysts formed at 5 % O-2 (p < 0.05). Compared with gene expression levels at 5 % O-2, which were arbitrarily set as 1, 20 % O-2 is associated with significantly higher expression of BAX (2.14 +/- 0.47), G6PD (2.92 +/- 1.06), MnSOD (2.87 +/- 0.88), and HSP70.1 (8.68 +/- 4.19). For all genes tested, no significant differences were found between 2 and 5 % O-2. The result suggests that development of cryopreserved human embryos from day 3 to blastocyst stage benefits from culture at 5 % O-2.