Abstract: Objective：To evaluate the effects of the lowered oxygen concentration (5% oxygen) in incubator during embryo culture on the outcomes of in vitro fertilization-embryo transfer (IVF-ET) for elderly women. Methods: The women aged ≥38 years who underwent IVF and fresh embryo transfer in our center from September 1, 2015 to June 1, 2017 were retrospectively analyzed. A total of 283 cycles were assigned into two groups according to the oxygen concentration in the incubator: the 5% oxygen concentration group (n=120) and the 20% oxygen concentration group (n=163). The normal fertilization rate, cleavage rate, available embryo rate, good quality embryo rate, clinical pregnancy rate, implantation rate and early abortion rate were compared between the two groups. Results: There were no significant differences in the normal fertilization rate, cleavage rate, available embryo rate, biochemical pregnancy rate, clinical pregnancy rate, implantation rate, early abortion rate and live birth rate between the two groups (all P＞0.05)，while the good quality embryo rate in the 5% oxygen concentration group was significantly higher than that in the 20% oxygen concentration group (P＜0.05). Conclusions: The lowered incubator oxygen concentration for the embryos of elderly women could obtain the higher rate of good quality embryo，but the effects on clinical pregnancy rate and implantation rate were not obvious.

Key words: Fertilization in Vitro, Embryo transfer, Oxygen concentration, Oxygen, Advanced age, Pregnancy outcome