Is the correlation between fetal oxygen saturation and blood pH sufficient for the use of fetal pulse oximetry?

Objectives: Fetal pulse oximetry was performed during labor in high-risk cases for fetal distress to determine the diagnostic value of this method. Methods: The fetal SpO₂ values were blinded from the obstetrician so that these values did not influence clinical decisions. Mean and lowest SpO₂ measurements for the last 30 min prior to either fetal scalp blood sampling or delivery were correlated with scalp pH or pH from the umbilical artery. Results: No significant correlation was found between pH and mean fetal oxygen saturation (correlation coefficient -0.02, p = 0.9). There was no significant correlation between pH and lowest fetal oxygen saturation (correlation coefficient 0.04, p = 0.84). Concerning the feasibility of the method, we found that only 23 of 65 included patients were suitable for analysis; in 20% of cases, we were not able to perform a SpO₂ measurement. Conclusions: None of three cases with pH below 7.05 would have been detected using mean SpO₂ over the last 30 min prior to fetal scalp blood sampling or delivery. Only one case would have been detected using the lowest SpO₂ measurement over this period. We conclude that fetal SpO₂ measurements during labor are of poor diagnostic value, with a disappointing feasibility and therefore are not ready for implementing into daily clinical practice.