Scalp blood lactate for intra‐partum assessment of fetal metabolic acidosis

OBJECTIVE: To study to what extent the fetal scalp blood lactate concentration during labor correlates with fetal scalp pH and base deficit, and metabolic acidosis at birth, and to suggest lactate cut-off values to serve as indicators for either reassurance or immediate intervention. DESIGN: A retrospective observational study. SETTING: Labor ward at a university medical center. SAMPLE: Fetal scalp and cord blood samples with acid-base and lactate values from 486 singleton pregnancies beyond 34 weeks' gestation. METHODS: The relation between lactate, pH and base deficit (BD) in fetal scalp blood was tested by Spearman's rho correlation coefficient. Lactate cut-off values indicating either reassuring fetal status or immediate intervention were estimated using percentile distribution and compared with pH and BD. MAIN OUTCOME MEASURES: Metabolic acidosis, defined as umbilical cord artery pH below 7.05 and BD calculated for the blood compartment above 12 mmol/l. RESULTS: After 127 (21%) exclusions, 486 cases were available for analysis. Fetal lactate values increased with evolving metabolic acidosis. Lactate concentration correlated with both pH (r=-0.50, p<0.01) and BD (r=0.48, p<0.01). Lactate <5.4 mmol/l indicated reassuring fetal status, whereas lactate ≥6.6 mmol/l indicated metabolic acidosis. Fetal lactate correlated better with either the absence or presence of metabolic acidosis at birth than did fetal pH and BD. CONCLUSIONS: In the case of a non-reassuring fetal heart rate, fetal scalp blood lactate provides more accurate information on fetal acid-base status than does pH and/or BD.