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

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 greater than or equal to 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, 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.