The acoustic environment and physiological responses of the fetus.

The acoustic environment of the fetus is composed of continuous cardiovascular, respiratory, and intestinal sounds that are punctuated by isolated, shorter bursts during maternal body movements and vocalizations. The distribution of sounds is confined to frequencies below 300 Hz. Additionally, vibrations on the external surface of the maternal abdomen can induce sounds inside the uterus. The half-round sound pressure contours in the abdomen during vibroacoustic stimulation differ from the circular distribution of contours resulting from airborne sound pressure exposure. The static and dynamic forces of the vibrator and the vibrator distance from the target are also factors in sound transmission. Responses to sound are best described in animals and include changes in behavioral state, brain bloodflow, auditory brainstem response, and local cerebral glucose utilization along the central auditory pathway.