Effect of oxygen concentration on in vitro fertilization and embryo culture in the human and the mouse

Abstract

To compare the effect of culturing oocytes, zygotes and embryos under low (5%) versus ambient (20%) oxygen conditions on human IVF results and on mouse blastocyst formation. A prospective, randomized study of 257 consecutive IVF treatment cycles in 186 couples undergoing oocyte retrieval for various reasons of infertility. Gametes and resulting embryos after IVF were alternately allocated to fertilization and culture either under a gas phase of 5% CO2/90% N2/5% O2, or 5% CO2/95% air (20% O2). Oocytes and embryos from randomly bred and hybrid mouse strains were randomly allocated to culture under either of the two gas phases. A university hospital-based IVF-ET program. In the human, rates of fertilization, embryonic development at the time of embryo replacement (42 to 46 hours after insemination), pregnancy, and implantation were compared. In the mouse, the rates of blastocyst formation were compared. Clinical pregnancies occurred in 24.2% versus 19.4% of retrievals when culture took place under low oxygen versus ambient oxygen conditions. Fertilization, embryonic development, pregnancy, and implantation rates did not differ significantly between the groups. Slightly higher blastocyst rates occurred when mouse embryos from hybrid strains were cultured under low oxygen compared with culture under ambient oxygen conditions, whereas no such difference in blastocyst rates was found in randomly bred mouse embryos. This study failed to demonstrate any improvement in human IVF results associated with the use of a gas mixture of 5% CO2/90% N2/5% O2 during the first two days of development compared with the use of 5% CO2 in air.