Fetal habituation to sound stimulus in various behavioral states.

The correlation between arousal state and fetal habituation was tested. Four behavioral states were determined according to fetal heart activity and movement pattern in 52 fetuses. Repeated wide low-frequency sound was used as external stimulus. Ceasing of response to 5 consecutive stimuli indicated habituation. The time from response to habituation was defined as habituation time. Although fetuses in a lower arousal state habituate more rapidly, the difference is not statistically significant.