Objective: Our aim was to determine whether supplemental oxygen during the second stage of normal labor affects cord blood gas and cooximetry values.
Study design: Patients at term pregnancy were prospectively randomized to the control or treatment group at the onset of the second stage of labor. The treatment group received 10 L/min oxygen by face mask, which result in a mean fractional inspired oxygen concentration of 0.81.
Results: There were 86 patients randomized into the study. In the oxygen group there were significantly more cord arterial pH values < 7.20 (9/41 vs 2/44, p < 0.05). The control group was compared with two subgroups of patients receiving oxygen: those receiving oxygen therapy for < or = 10 minutes and those receiving oxygen for > 10 minutes. Analysis of variance demonstrated significant differences (7.285 +/- 0.058, 7.312 +/- 0.056, 7.237 +/- 0.064; F test 8.3, p = 0.0005). Among several independent variables, regression analysis demonstrated that only duration of oxygen therapy had a significant inverse relation to cord arterial pH (F test = 15.6, p = 0.0002).
Conclusions: Prolonged oxygen treatment during the second stage of normal labor resulted in a deterioration of cord blood gas values at birth.