The effect of intrapartum prolonged oxygen exposure on fetal metabolic status: secondary analysis from a randomized controlled trial.

Objective: The aim of the study is to assess the effect of maternal prolonged oxygen exposure during labor on fetal acid-base status, fetal heart rate tracings, and umbilical cord arterial metabolites. Design: The study was conducted as a secondary analysis. Settings: The study was set in three tertiary teaching hospitals in Beijing, China. Participants: Approximately 140 women in the latent phase of labor with no complications participated in the study. Intervention: Participants were randomly allocated in a 1:1 ratio to receive either 10 L of oxygen per minute in a tight-fitting simple facemask until delivery or room air only. Main outcome measures: The primary outcome was the umbilical cord arterial lactate. Results: Baseline demographics and labor outcomes were similar between the oxygen and room air groups; the time from randomization to delivery was 322 ± 147 min. There were no differences between the two groups in the umbilical cord arterial lactate (mean difference 0.3 mmol/L, 95% confidence interval -0.2 to 0.9), the number of participants with high-risk category II fetal heart rate tracings (relative risk 0.94, 95% confidence interval 0.68 to 1.32), or the duration of those high-risk tracings (mean difference 3.6 min, 95% confidence interval -9.3 to 16.4). Prolonged oxygen exposure significantly altered 91 umbilical cord arterial metabolites, and these alterations did not appear to be related to oxidative stress. Conclusion: Maternal prolonged oxygen exposure during labor did not affect either the umbilical cord arterial lactate or high-risk category II fetal heart rate tracings but might result in alterations to the umbilical cord arterial metabolic profile. Clinical trial registration: www.clinicaltrials.gov, identifier NCT03764696.