How well does reflectance pulse oximetry reflect intrapartum fetal acidosis?

The purpose of this study was to determine the sensitivity and specificity for acidosis of intrapartum fetal oxygen saturation measured by reflectance pulse oximetry. Intrapartum fetal oxygen saturation values per labor stage were correlated with umbilical artery pH, base excess and PCO(2) by regression analysis. Receiver operating characteristic curve analysis was performed with the use of historic umbilical arterial cutoff values; a fetal oxygen saturation cutoff range with optimal sensitivity and specificity was calculated. Mean fetal oxygen saturation was 42.8%, over the mean 132 minutes of 107 recordings. Overall areas under the sensitivity and specificity curves were 0.77 for pH and PCO(2), decreasing sharply toward birth; all areas for base excess were poor (approximately 0.5). Depending on stage and umbilical artery parameter, fetal oxygen saturation cutoffs were 33% to 36%, with sensitivities of 0.67 to 0.8 and specificities of 0.62 to 0.90. Fetal oxygen saturation sensitivities and specificities for acidosis do not yet justify the supplementation of cardiotocography with routine reflectance pulse oximetry.