Piezoelectric vibrator-stimulated potential and heart rate accelerations detected from the fetus.

OBJECTIVES: The fetus is well known to have a substantial capacity for sound recognition in the uterine environment. The aim of this study was to develop a sound stimulus system equipped with a piezoelectric vibrator (PV), record the PV-stimulated potential (PVSP) of the fetus and monitor changes of the fetal heart rate (FHR) under PV stimulation. METHODS: The relationship between the input voltage applied to a piezoelectric vibrator and the sound pressure generated in the uterus was calibrated based on a model of the maternal abdomen. Fourteen fetuses for the measurement of the PVSP and 22 fetuses for the measurement of the heart rate changes from low-risk pregnant women were recruited. RESULTS: The PVSP responses were obtained in 9 out of 14 fetuses. All the tested fetuses accelerated the FHR after the 2 kHz tone stimulation at 70 dB intensity generated by PV from 32 to 37 weeks gestational age. CONCLUSIONS: Using a newly developed sound stimulus system equipped with PV, the electric responses of a fetus recorded from electrodes placed on the mother's abdomen may be closely related to the auditory evoked response. Significant accelerations of FHR were objectively, accurately and readily obtained after the sound stimulation.