Oxygen Tension on Human Embryonic Development

In mammals, uterine environment is at low oxygen concentration (2-8% O2). Thus, human embryo culture under low O2 tension (5%) is now recommended by European Society of Human Reproduction and Embryology (ESHRE) revised guidelines for good practices in in vitro fertilization (IVF) labs. Indeed, hypoxia seems to improve embryo quality at cleavage and blastocyst stages, presumably by reducing damages of oxidative stress (OS). Nevertheless, recent meta-analyses concluded only with a low evidence to a superiority of hypoxia on IVF/ICSI outcomes. Furthermore, a study on mouse embryos suggested a negative impact of OS only at cleavage stage. The aim of the present prospective randomized study was to investigate this hypothesis for the first time in human embryos.