The effect of intrapartum oxygen supplementation on category II fetal monitoring

The administration of maternal oxygenation (O₂) is a commonly used resuscitation technique for fetuses with category II electronic fetal monitoring (EFM) patterns. In cases of recurrent fetal decelerations, the goal of maternal O₂ supplementation is to increase fetal oxygenation. Yet, evidence to support this technique is limited and based on literature published 40 years ago. However, a recent study compared O₂ supplementation with room air (RA) in patients with category II EFM patterns and found that RA was not inferior to O₂ supplementation. The aim of the current study was to examine the effect of O₂ supplementation in patients with category II EMF patterns on pregnancy outcomes. This study was a randomized controlled trial, which assigned patients in active labor and with category II EFM patterns to either 10 L/min of O₂ supplementation or RA. Included were patients with normal pregnancies admitted for labor induction or spontaneous delivery, for whom EFM data were available. Excluded were patients with major fetal anomalies, multiple gestations, and maternal hypoxia. Patients with category II EFM patterns requiring intrauterine resuscitation were randomly assigned to either the O₂ group or RA group. EFM data were collected 60 minutes before and after randomization. The primary outcome was represented by a composite of high-risk category II features, including recurrent variable, recurrent late, and prolonged decelerations; minimal variability; or tachycardia. Secondary outcomes were the individual components of the primary outcome, total deceleration area, and resolutions of recurrent decelerations. Of the 114 patients included in the analysis, 57 were randomized to the O₂ group and 57 to the RA group. The O₂ group and RA group had similar rates of the primary outcome (ie, composite of high-risk category II features) within 60 minutes of randomization (42.1% vs 47.4%; relative risk [RR], 0.9; 95% confidence interval [CI], 0.6-1.3). No differences were observed for recurrent variable, recurrent late, and prolonged decelerations in the O₂ group versus RA group (P = 0.71, 0.52, and 0.84, respectively), as well as minimal variability (P = 1.00). Tachycardia did not present in either group. In the O₂ group, no differences were observed for the primary and secondary outcomes. Likewise, no differences were observed for the primary and secondary outcomes within the RA group. The rates of resolution of recurrent decelerations were similar (75.4% in the O₂ group vs 86.0% in the RA group; P = 0.15), as was the total deceleration area (P = 0.22). In this study, maternal O₂ supplementation was not observed to improve decelerations, resolve recurrent decelerations, nor hasten recurrent decelerations. The study suggests that O₂ administration in cases of high-risk category II EFM patterns may need to be revisited given the lack of benefit and the risks associated with hyperoxygenation.