Acoustic stimulation as a diagnostic test: comparison with oxytocin challenge test

The usefulness of an acoustic stimulation test as a marker of fetal well-being was evaluated in a randomized controlled study of 121 pregnant women exhibiting a non-reactive fetal non-stress test at term. The women were randomly divided into two groups; those in the first group (n = 62) underwent an acoustic stimulation test immediately prior to an oxytocin challenge test, while those in the second (n = 59) underwent an oxytocin challenge test only. Fetal response to the acoustic stimulation was non-reactive in 22.5% of the women tested in the first group. The incidence of abnormal oxytocin challenge test among the women who were previously subjected to an acoustic stimulation was somewhat lower than among those who did not (14.5% vs. 23.7%), but the difference was not significant. In the prediction of an abnormal oxytocin challenge test, a non-reactive acoustic stimulation test had a sensitivity of 100%, a positive predictive value of 64% and a specificity of 91%. As a single test for the prediction of fetal distress in labor (n = 62), the acoustic stimulation test had a specificity and a positive predictive value similar to those of the oxytocin challenge test (n = 121), and its sensitivity was even higher (88% vs. 71%). We conclude that the acoustic stimulation test is at least as reliable as the oxytocin challenge test in the evaluation of fetal well-being in women exhibiting a non-reactive non-stress test at term.