What is the critical threshold of oxygen saturation for the fetus?
Published animal studies suggest that fetal imbalance, as indicated by the onset of metabolic acidosis, may begin when preductal saturation is between 25% and 35%.21-23 These studies find that there is no sign of hypoxia when saturation exceeds 35%. A prospective multicenter human observational study in Germany was undertaken to quantify the predictive agreement between FSpO2 and fetal scalp pH when used to assess fetal status during periods of nonreassuring fetal heart rate patterns during labor. The results of 50 pairs of FSpO2 readings and simultaneous scalp pH values from 46 patients (one patient contributed 5 data pairs) demonstrated that setting the critical threshold value of FSpO2 at 30% yielded a reasonable balance between sensitivity and specificity for the prediction of fetal acidosis (defined as scalp pH < 7.20).24 The primary goal of fetal oxygen saturation monitoring is to improve the overall specificity of diagnosis in the context of an already nonreassuring, and thus, h
