Human fetal response to vibroacoustic stimulation as a function of stimulus duration.

The effect of stimulus duration on the initial fetal heart rate (FHR) acceleration response was evaluated by assessing its amplitude and span following a single vibroacoustic stimulation with durations of 0 (sham), 1, 3, or 5 seconds. Statistically significant differences were observed in the mean amplitude and duration of acceleration in groups 3 and 5 when compared with groups 0 and 1 (P less than .05). In addition, groups 3 and 5 demonstrated significantly greater fetal reactivity than group 0 and a decrease in testing time over groups 0 and 1 (P less than .05). Our results suggest that the magnitude of the FHR acceleration response is dependent on the duration of the stimulus. Furthermore, a 3-second sound stimulus appears to be adequate for a shift to the fetal behavioral "awake" state.