Vibroacoustic stimulation and fetal behavioral state in normal term human pregnancy

Vibroacoustic stimulation may affect human fetal behavior. Continuous graphic records of simultaneous ultrasonographic observations of fetal activities and electronic fetal heart rate tracings of 30 normal term fetuses were examined visually for the occurrence of behavioral state 30 minutes before and after 3 seconds of vibroacoustic stimulation. After vibroacoustic stimulation, the total time spent in state 1 decreased significantly, that spent in state 4 increased significantly, and times spent in state 2 and indeterminate state (no state established for at least 3 minutes) were unchanged. No fetus exhibited state 3 before or after vibroacoustic stimulation. State 4 occurred in 22 fetuses after vibroacoustic stimulation with a duration of at least 30 minutes in four fetuses, and was noted in all fetuses in pre-vibroacoustic stimulation state 1 and 11 of 16 fetuses in pre-vibroacoustic stimulation state 2. Fetal heart rate accelerations occurred within 10 seconds after vibroacoustic stimulation in 94% of the fetuses studied regardless of their prior behavioral state. The variation in the onset and duration of behavioral state responses in most fetuses after vibroacoustic stimulation may depend on previous behavioral state and could be important for interpretation of antenatal assessment that uses this stimulus.