Measurement of auditory evoked response for fetal hearing screening test

Abstract

In order to examine hearing ability in fetuses, we have observed auditory evoked response induced by sound stimulation. The sound device consisted of a function generator, a piezo driver and a piezoelectric vibrator. The piezoelectric vibrator and two electrodes were positioned on the surface of the mother's abdomen above the head of fetus. Tone burst sound stimuli of 2 kHz, 70 dB were provided to the fetus through bone conduction. Measurement of brain waves of fetuses were performed in healthy pregnant women in the period of 33 to 38 weeks of gestation. Each subject was measured three times and potential curves were obtained. Then, correlation factors were calculated between the three potential curves to detect the brain waves by estimating the similarities of the curves. Simultaneously we evaluated a time variation of the correlation factors after stimulus. As a result, brain waves were detected 17 out of 19 subjects. The latencies of brain response to the sound stimuli in 35 - 36 weeks gestational age fetuses were longer than that in 37 weeks.