How well does reflectance pulse oximetry reflect intrapartum fetal acidosis?

Objective: The purpose of this study was to determine the sensitivity and specificity for acidosis of intrapartum fetal oxygen saturation measured by reflectance pulse oximetry. Study Design: Intrapartum fetal oxygen saturation values per labor stage were correlated with umbilical artery pH, base excess and P 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. Results: 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 P 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. Conclusion: Fetal oxygen saturation sensitivities and specificities for acidosis do not yet justify the supplementation of cardiotocography with routine reflectance pulse oximetry. (Am J Obstet Gynecol 2002;186:1351-7.)