Abad MR, Serra V, Gámiz P, et al. - Researchers here examined if and how the oxygen concentration during 3-day embryo culture affects obstetric and neonatal outcomes. Data from a previous randomized controlled trial examining clinical pregnancy outcomes was assessed for this secondary analysis. In total, they analyzed 1,125 consecutive oocyte donation cycles utilizing ICSI or IVF and Day 3 embryo transfers between November 2009 and April 2012. From the eligible 1,125 cycles, they performed random allocation of 564 to a reduced O₂ tension group (6% O₂) and 561 cycles to an air-exposed group (20% O₂) based on a computer-generated randomization list. However, the 6% and 20% O₂ groups had 50 and 62 cycles, respectively, that did not reach embryo transfer. Per outcomes, there appeared no effect of oxygen concentration during 3-day embryo culture on obstetric and neonatal outcomes measured.