A controlled randomized trial evaluating the effect of lowered incubator oxygen tension on live births in a predominantly blastocyst transfer program†

The potentially damaging effect of free O(2) radicals to cultured embryos may be reduced by adding scavengers to the culture media or by reducing the incubator O(2) levels. However, lowering the O(2) in the culture environment can be expensive, troublesome and may not be justifiable. The objective of this study was to evaluate the effect of lowered incubator O(2) tension on live birth rates in a predominately Day 5 embryo transfer program. Two hundred and thirty first-cycle women undergoing routine IVF or ICSI with ejaculated sperm were randomized in a prospective clinical trial and stratified for patient age and physician. Embryos of patients were randomly assigned for culture in either a 21% O(2) (atmospheric) or 5% O(2) (reduced) environment. Clinical endpoints monitored were rates of implantation, clinical pregnancy, live birth and blastocyst cryopreservation. Embryos cultured in a 5% O(2) environment consistently resulted in higher rates of live birth implantation (106/247, 42.9% versus 82/267, 30.7%; difference of 12.2% with 95% confidence interval (CI) of 3.9-20.3, P = 0.005) and live births (66/115, 57.4% versus 49/115, 42.6%; difference of 14.8% with 95% CI of 1.9-27.0, P = 0.043) when compared with rates among women whose embryos were cultured in an atmospheric O(2) environment. The overall increase in live births demonstrated by this study indicates that the effort and expense to culture embryos in a low-O(2) environment is justified. The study was registered at clinicaltrials.gov. NCT00708487.