vibroacoustic stimulation vibroacoustic stimulation vibroacoustic stimulation (vas), sometimes referred to as fetal vibroacoustic stimulation or fetal acoustic stimulation test (fast), is the application of a vibratory sound stimulus to the abdomen of a pregnant woman to induce fhr (fetal heart rate) accelerations. the presence of fhr accelerations reliably predicts the absence of fetal metabolic acidemia. vibroacoustic stimulation is typically used during a nonstress test (nst). in 2013, the cochrane database of systematic reviews concluded that there was insufficient evidence from randomized trials to support its use to assess fetal well-being in labor. a related cochrane review, however, concluded that its use in antenatal testing did reduce the incidence of non-reactive cardiotocography and the overall testing time.