Toward implementation of lactate compared with pH in fetal scalp blood sampling during labor: A clinical comparative single‐center study

INTRODUCTION: Since 60 years, pH measurement in fetal scalp blood samples (FBS) is used to diagnose fetal hypoxia during labor, although the last three decades lactate measurement in FBS has been increasingly used as a safe alternative with a lower chance of failure. However, studies demonstrating the direct relation between lactate and pH in FBS with the currently used measurement systems are lacking. Therefore, clinical acceptance and implementation is impeded. This study investigated the relation between lactate and pH in FBS and derived an appropriate lactate cutoff value. MATERIAL AND METHODS: This observational prospective single-center study included 263 FBS in the period of 8 months. After collection of FBS, pH was assessed first (iSTAT®), after which lactate was assessed (StatStrip® Lactate 2). Clinical decisions were based on pH results only. Our primary objective was to assess the correlation between lactate and pH in FBS and to establish a lactate cutoff value for ruling out a low Apgar score at 5 minutes and neonatal acidosis, with corresponding sensitivity and specificity as secondary outcomes. Diagnostic performance of lactate was assessed by using the area under the curve (AUC) of the receiver operation characteristic curve (ROC curve), from which cutoff values were derived. RESULTS: In FBS, lactate and pH showed a moderate inverse linear correlation (r = -0.53). The AUC of the ROC curve was 0.88 (0.83-0.93), indicating a good diagnostic performance of lactate to identify an abnormal pH (pH