Purpose of Proposed Study This study seeks to compare clinical outcomes of embryos cultured at 2% oxygen concentration and 5% oxygen concentration after compaction. The primary outcome under study will be live birth rate. Secondary outcomes will include miscarriage rate, gestational age at delivery, birth weight at delivery, embryo blastulation rate, embryo ploidy status (aneuploid or euploid) and morphologic parameters (expansion, inner cell mass grade, trophectoderm grade). The cumulative live birth rate of all embryos that originate from the study stimulation cycle will also be collected and analyzed. This will theoretically reveal whether any advantage in the number of available blastocysts for transfer translates to greater reproductive efficiency when extended culture is performed at 2% oxygen.