Fetal transcutaneous PCO2 measurements during labour.

The departments of Obstetrics and Gynaecology of the Universities of Bonn and Copenhagen and the Free University of Amsterdam cooperated in the European Community Concerted Action Project 'New methods for Perinatal Surveillance'. In 95 patients fetal transcutaneous PCO2 (tcPCO2) recording (measuring temperature 41 degrees C) during labour was evaluated regarding its clinical applicability. During the first stage of labour fetal tcPCO2 was rather stable at a level of 7.3 +/- 1.4 kPa. In the second stage there were marked differences between the three subpopulations. In the first stage of labour the correlation between tcPCO2 and PCO2 in fetal blood samples was 0.38 (P = 0.02) and in the second stage -0.20 (P = 0.36). The correlation of fetal tcPCO2 with umbilical artery PCO2 was 0.30 (P = 0.01) and with pH -0.30 (P = 0.01). Using a fetal tcPCO2 level of 8.0 kPa as a cut-off point to predict an umbilical artery pH less then 7.20, sensitivity was 88%, specificity 65%, positive predictive value 29% and negative predictive value 97%. The likelihood ratio of a positive test was 2.47 and of a negative test 0.13. It is concluded that fetal tcPCO2 possibly can be an additional tool to exclude fetal acidosis. In case of values above 8.0 kPa further evaluation of the fetal acid-base balance is indicated.