Stimulation of human fetuses with sound and vibration.

Forty pregnant women between 30 and 42 weeks' gestational age were studied to examine the effects of external sound and vibration on the fetal heart rate. A significant increase in the mean duration and amplitude of the first acceleration after sound stimulus was found when these values were compared with the control values. Conversely the mean time to the first acceleration in the control period was greater than that in the stimulated period. There was a significant increase in the mean duration of fetal heart rate accelerations, the mean amplitude of fetal heart rate accelerations, and the total time spent in accelerations up to 15 minutes after the sound stimulus as compared with the control period. There was no change in the number of accelerations following the sound stimulus compared to control. These data suggest that vibratory acoustic stimuli may influence patterns of fetal heart rate during human pregnancy.