This study was conducted to assess the role of maternal oxygen
   administration during the second stage of labor on umbilical cord blood gas
   values.  This study was done in Fatemieh hospital on 160 pregnant women
   who were admitted for vaginal delivery and had the inclusion criteria.

          A group of 80 women with term pregnancy were administrered oxygen
   during the second stage of labor and another group of 80 women with
   term pregnancy acted as control (Randomized clinical trial). Umbilical cord
   blood gas values were measured immediately  after birth. Apgar score and
   duration of oxygen administration of two groups were documented. Blood
   gas values , apgar score , duration of oxygen therapy , duration of second
   stage of labor also were recorded.

          In the case group: The umbilical artery pH value was 7.25 (7.06-7.38) and
   umbilical vein pH was > 7.31 (7.13-7.45). Umbilical artery pH in the control
   group was 7.28 (7.08-7.96) and umbilical vein pH was 7.31 (7.02-7.44). There
   was no statistically difference between means of umbilical cord blood gas
   values of the groups (case and control , P>0.05). There was perfect negative
   correlation between umbilical cord blood gas values and duration of
   oxygen administration (P<0.001 , r =-0.5).

          In fact oxygen administration in second stage of labor has not any
   effect on cord blood gas analysis , provided that no clinical evidence of
   danger for mother or fetus present. Besides prolonged oxygen
   administration can cause  decrease in arterial pH.