Various fetal heart rate (FHR) tests including nonstress test (NST) have been used for antepartum fetal surveillance. The test using FHR reponse to externally applied sound, namely acoustic stimulation test (AST), is currently being used as an alternative tool of NST. However, there were only few reports regarding computerized FHR analysis in the AST. Individual subjective analysis of FHR tracings can be replaced with an automated computerized objectiy analysis system and the accurate recording and analysis of FHR records is now possible using personal computers. In this study, the author prospectively analyzed the FHR response after acoustic stimulation using computerized FHR analysis system, HYFM-1.
Sixty five normal term and preterm pregnancies entered to this study. After acoustic stimulation with 90 Decibel and 500 Hertz using programmable acoustic stimulator (8031-CPU, 70-120 Decibel of sound intensity level range, 10-10,000 Hertz of frequency range), the changes of baseline FHR, variability, number of fetal movements and loss of signal were analyzed using HYFM-1.
In normal term pregnancies, the baseline FHR, variability, and number of fetal movements were significantly increased after acoustic stimulation. In preterm pregnancies, the baseline FHR and variability were also increased significantly except number of fetal movements, although absolute value of fetal movement was somewhat increased after acoustic stimulation. Using qualitative analysis of baseline FHR, 15 of 43 term pregnancies(34.9%) revealed FHR increments more than 15 bpm, however there were only 13.6% (3% of 22 patients) FHR increment over 15 bpm in preterm pregnancies. This difference was statistically significant. It would be suggested that the increment of baseline FHR reflect the central nervous system maturation of fetus at least in term pregnancies.
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