DR O2 exposure and SpO2: SpO2 will be downloaded from pulse oximeters used during resuscitation as per Masimo pulse oximeter guidelines using TRENDCOM software (Masimo, Irvine, CA). Investigators have described and successfully performed acquisition of such data in our previous study. Resuscitation interventions including changes in FiO2 will be recorded at 30 seconds intervals by the OB circulating nurse whose sole responsibility is to record resuscitation details in a pre-specified record sheet as per routine practice at Parkland Hospital.