Prediction of umbilical artery base excess by intrapartum fetal oxygen saturation monitoring

Abstract

OBJECTIVE: Our purpose was to evaluate the predictive value of intrapartum fetal oxygen saturation as monitored by reflectance pulse oximetry (Spo 2) for metabolic acidosis at birth. STUDY DESIGN: An observational study was carried out on intrapartum patients at ≥35 weeks' gestation having either a nonreassuring fetal heart rate pattern, intrauterine growth restriction, or thick meconium. Fetal oxygen saturation monitoring was performed with use of the Nellcor N-400 monitor and the FS-14 fetal oxygen sensor. Mean values of Spo 2 from the last 30 minutes of monitoring were correlated with umbilical artery base excess and pH at birth, with use of regression analysis, whereas the prediction of acidosis by Spo 2 at different thresholds was tested with use of receiver-operator characteristic curve calculations. RESULTS: Fifty-four patients met the criteria for data analysis, with a mean Spo 2 monitoring time of 150 ± 124 minutes (SD) and a mean signal loss of 30% ± 20%. Mean fetal Spo 2 for the last 30 minutes of monitoring averaged 42.1% ± 9.9% and, for individual patient studies, correlated significantly with calculated oxygen saturation in the umbilical vein ( r = 0.52, p < 0.001) and in the umbilical artery ( r = 0.34, p = 0.02) as measured at birth. However, the correlation with umbilical artery base excess values at birth was somewhat weaker ( r = 0.30, p < 0.05), as was the correlation with umbilical artery pH values ( r = 0.26, p = 0.05). Receiver-operator characteristic curve calculations were all nonsignificant when Spo 2 from the last 30 minutes of monitoring was used as a diagnostic test for predicting acidosis at birth. CONCLUSIONS: Intrapartum fetal Spo 2 as monitored in the current study was of limited use as a diagnostic test for predicting acidosis at birth, regardless of the Spo 2 cutoff value used. (Am J Obstet Gynecol 1997;177:775-9.)