This initial study was designed to specifically evaluate the developmental performance of embryos in both conditions. However, there are also some pregnancy data available from those patients who have proceeded to transfer these embryos. In this initial study, culture conditions had no impact on the decision of which embryo to transfer. This was blinded to embryologists and patients and only typical morphology criteria were utilized. Again, of patients who have proceeded to embryo transfer, embryos that had been cultured in 2% oxygen have performed better than those exclusively in 5% (88.9% [16/18] vs. 62.5% [15/24]