Abstract: ［Abstract］ Objective〖HTSS〗〓To assess the effect of the use of low flow  maternal oxygen during the second stage of labor on the umbilical cord artery pH and pregnancy outcome. 
〖HTH〗〖WTHZ〗Methods〖HTSS〗〓In this randomized controlled trial(RCT), 1 100 women undergoing the second stage of labor who had no complications were randomly allocated to receive either oxygen at a flow rate of  2 L/min or sham at a flow rate of  0 L/min by the nasal cannula. Management of labor were similar in the two groups. Primary outcome was umbilical cord artery pH, and other pregnancy outcomes were recorded.
〖HTH〗〖WTHZ〗Results〖HTSS〗〓There were no significant differences between the two groups in the fetal distress rate, neonatal asphyxia rate, instrumental vaginal delivery rate and cesarean section rate.
〖HTH〗〖WTHZ〗Conclusion〖HTSS〗〓The use of 2 L/min maternal oxygen during the second stage of labor could not affect the umbilical cord artery pH，and could not improve the pregnancy outcome.

Key words: fetal distress, labor stage, second, asphyxia neonatorum