Comparison of abdominal ECG and phonocardiography for instantaneous fetal heart rate detection

The authors present a system for the assessment of the reliability of processed fetal phonocardiography to detect beat to beat variations when it is compared with abdominal ECG. Eighteen volunteers with low risk pregnancies, between 32 to 40 weeks of gestation and no evidence of labor, were studied. In order to obtain beat to beat interval, fetal heart sounds were recorded, the peaks of the first heart sounds were clearly evident, after filtration, derivation and envelope detection of the signal. These peaks were identified by means of amplitude and timing criteria. Besides, beat to beat intervals were accurately measured. Statistical comparison was done with abdominal ECG, whose fetal RR were determined, and showed nonsignificant difference of mean (p>0.05), low mean relative error (1.03) and no bias (ri=0.96-0.98). The authors conclude that instantaneous fetal heart rate estimation by phonocardiography assures an accurate measurement of beat to beat intervals