Fetal distress diagnosis using heart rate variability analysis: design of a high frequency variability index

Routine monitoring of Fetal Heart Rate (FHR) during labor enables diagnosis of fetal distress and appropriate management by the medical staff. Diagnosis of fetal distress relies mainly on a subjective visual assessment of FHR variations using baseline level, oscillations magnitude, decelerations and their time-relation to the parturient uterine contractions. Strong intra and inter-observer discrepancies exist with this widely used technique, and sometimes requires fetal scalp blood sample pH measurement, which is not fully reliable either. Gold standard assessment of fetal distress relies on blood pH measurement after the birth. In this paper we describe a new method for fetal distress diagnosis based on FHR variability analysis, measuring the high frequency content of FHR as a High Frequency Variability Index (HFVI). We tested this new index on 21 fetuses where FHR was recorded during labor for an observational clinical trial. FHR recordings were separated in two groups given the fetal arterial pH obtained after birth: group 1 - no distress, pH >= 7.15, N=16 and group 2 - fetal distress, pH 7.15, N=5. The new index was significantly higher in group 1 than in group 2 (non parametric Mann Whitney U-test, p=0.01).