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 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.
^East, C. E.; Smyth, R. M.; Leader, L. R.; Henshall, N. E.; Colditz, P. B.; Lau, R.; Tan, K. H. (2013). East, Christine E, ed. "Vibroacoustic stimulation for fetal assessment in labour in the presence of a nonreassuring fetal heart rate trace". The Cochrane Library1: CD004664. doi:10.1002/14651858.CD004664.pub3. PMID23440793.edit