Abad MR, Serra V, Gámiz P, et al. - Researchers investigated the effect of oxygen concentration during 3-day embryo culture on obstetric and neonatal outcomes. They performed a secondary analysis of a previous randomized controlled trial examining clinical pregnancy outcomes. A total of 1,125 consecutive oocyte donation cycles utilizing ICSI or IVF and Day 3 embryo transfers were analyzed in this study. They performed random allocation of the whole cohort of donated oocytes from patients who agreed to participate in the study to a reduced O2 tension group (6% O2) or an air-exposed group (20% O2). From the 1,125 eligible cycles, they allocated 564 to the 6% O2 group and 561 cycles to the 20% O2 group. The groups were similar in the number of livebirths per embryo transfer, pregnancy complications or neonatal outcomes. Per these findings, there seems no influence of oxygen concentration during 3-day embryo culture on the obstetric and neonatal outcomes measured.