The effect of maternal low flow oxygen administration during the second stage of labour on umbilical cord artery pH: a randomised controlled trial

Objective To assess the effect of maternal low flow oxygen administration during the second stage of labour on umbilical cord artery pH. Design A randomised controlled trial. Setting A tertiary teaching hospital in China. Population Women in the second stage of labour with no complications. Methods About 443 women were randomly allocated to receive either supplemental oxygen at a flow rate of 2 l/min or a sham supplementation by nasal cannula. Healthcare providers, women and outcome assessors were blinded to allocation. Main outcome measures Umbilical cord artery pH and fetal heart rate (FHR) pattern. Results Baseline characteristics were similar between the two groups. There were no significant differences between the two groups in the umbilical cord artery pH [median 7.261, interquartile range (IQR) 7.228–7.295 versus 7.266 (IQR 7.232–7.297), P = 0.64], the proportion with pH less than 7.2 [30/219 versus 34/224, P = 0.66, RR (relative risk) 0.9, 95% CI 0.57–1.42], and the proportion with normal FHR pattern (147/219 versus 153/224, P = 0.79, RR 0.98, 95% CI 0.86–1.12). Maternal partial pressure of dissolved oxygen was significantly higher in the oxygen group than in the sham group [median 150.0 mmHg (IQR 142.6–156.7) versus 112.0 (IQR 104.8–118.3), P < 0.001], whereas carbon dioxide was significantly lower in the oxygen group than in the sham group (mean difference −1.1, 95% CI −2.1 to −0.1, P = 0.03). Conclusion The use of 2 l/min maternal oxygen during the second stage of labour did not adversely affect either the umbilical artery pH or the FHR pattern distribution. Tweetable abstract No difference in abnormal fetal acid base or normal heart rate if maternal O2 given, randomised trial finds.