[Study of fetal responses to external vibratory acoustic stimulation]

Effects of a 5-second external vibratory acoustic stimulation (VAS, 500 Hz, 75 db) were studied in 155 healthy pregnant women from 34 to 41 weeks' gestational age on the fetal heart rate and gross fetal body movement. Fetal behavioral states were also studied in 88 out of the 155 patients. The following results and conclusions were obtained. 1) VAS induced significant increases in the fetal heart rate baseline, the mean amplitude, the mean duration, and the mean time spent % of fetal heart rate accelerations and gross fetal body movements. 2) VSA induced significant changes in fetal behavioral states at states 1F and 3F, but no changes in states 2F and 4F. 3) Reaction to VAS was recognized also in the low birth weight (less than 2,500 g) group, but the duration of the reaction was shorter than that in the normal (greater than or equal to 2,500 g) group. 4) By lowering the incidence of false non reactive NST with VAS test, it was possible to predict the fetal prognosis better than NST alone. 5) Inasmuch as VAS changed the fetal behavioral state from resting phase to active phase, the use of VAS in addition to NST was very helpful in more accurate understanding of fetal heart rate monitoring.