Distribution of observed patterns in fetal transcutaneous oxygen tension.

The interaction between intrauterine pressure, fetal heart rate, and fetal transcutaneous oxygen tension (tcPO2) may be classified into 10 pattern types. Eight of them indicate the reduction in fetal tcPO2 caused by uterine contractions and by fetal heart rate decelerations. Two pattern types show the effect of stasis and of pressure resulting in decreased fetal tcPO2. In 32 recordings from Uppsala, Sweden, and 11 from Zurich, Switzerland, 1,161 contractions were analyzed. A similar distribution of the patterns was found in the two hospitals in uncomplicated deliveries in the first stage of labor. In 15% of the contractions in the first stage of labor, fetal tcPO2 was affected by stasis or pressure, whereas this occurred in 48% of the 265 contractions in the second stage of labor. Thus, in most instances, fetal tcPO2 should be expected to give reliable information in the first stage, whereas the stasis and the pressure pattern must be recognized for the evaluation of fetal tcPO2 in the second stage of labor.