Noninvasive fetal ECG mode fetal heart rate monitoring by adaptive digital filtering

Beat-to-beat variability (BTBV) of the fetal heart rate (FHR) is considered an indication of the neural integrity and is an important prognostic indicator of fetal well-being. We report the initial evaluation of a recently developed abdominal fetal ECG (AFECG) mode of FHR monitoring using Adaptive Digital Filtering (ADF) to accurately obtain BTBV noninvasively. Five women in labor at term were monitored with the direct fetal scalp electrode (FSE) and simultaneously with the AFECG using ADF. A computer analysis of 3298 seconds (55 minutes) of data provided a one-to-one comparison of the R-R intervals. One analysis of the direct FSE data with a second simultaneous analysis from the same electrode, to serve as control, was compared with the noninvasive AFECG data. The study group has a standard deviation of only 1.50 bpm compared to 0.79 bpm for the control group. The AFECG method agrees with the direct FSE method within 1 bpm for 92.6% of the reported R-R intervals and within 2 bpm for 98.9% of the reported intervals. This new noninvasive AFECG technique with ADF provides a continuous record of instantaneous FHR and BTBV that may be relied upon to provide an accurate continuous clinical record. The reliability of the technique has yet to be determined over a wide range of subjects.