The Effect of the Signal Loss on the Fetal Heart Rate Variables

Yang, J H; Park, M I; Song, J C

Abstract

The accurate assessment of the antenatal fetal well-being has become important and essential in modern obstetrics. The fetal heart rate [FHR] monitoring has gained wide acceptance as an useful clinical test for fetal well-being. The nonstress test[NST], which recognizes fetal movements associated FHR accelerations as a measure of fetal well-being and normalcy is widely used. Most results of the NST were interpreted with visual method. But the analysis of FHR records by conventional visual interpretation has many weak points, especially, in unattainable variability, mean baseline fetal heart rate, acceleration, and inevitable signal loss. The accurate data recording and analysis of FHR are now possible by using computer and it is also possible that the objective, precise and comparative data analysis of the records with this computerized analysis system. We had developed a computerized fetal heart rate interpretation system[HYFM-1]. The system hardware is consisted of a FHR monitor with autocorrelation[Corometrics 115] and serial board[6808] interfaced to an IBM Pentium computer. Output devices are consisted of a laser printer and a plotter. There are many reports about the FHR variability, fetal movement, and acceleration, but not in the signal loss. Using the HYFM-1, the effect of the signal loss on the FHR monitoring in preterm and term pregnancies was evaluated. Of 3,038 normal pregnancies, the mean signal loss was 7.1%. As the gestational age advanced, the mean baseline FHR, signal loss, and fetal movement were decreased. With the increasing of the signal loss, the fetal movement, mean baseline FHR and FHR variability were increased and the most sensitive NST variable with the signal loss change was FHR variability in the study.