Determinants of fetal heart rate response to vibroacoustic stimulation in labor.

To determine whether the fetal heart accelerates in response to a sound stimulus in labor, 40 women at various stages of labor were chosen at random to receive either a vibroacoustic stimulus or sham stimulus over the fetal head. Subsequent fetal heart rate (FHR) accelerations occurred to a significantly greater extent in study patients. One hundred thirty-two high- and low-risk patients were studied to determine correlations between the acceleration response and other maternal and fetal variables. There was a statistically significant negative correlation between the heart rate response to stimulation and three maternal variables: the degree of cervical dilation, the presence of ruptured membranes, and use of epidural anesthesia. The degree of fetal response did not correlate significantly with fetal distress at delivery or abnormal FHR tracings at the time of stimulation. Fewer than one-fifth of the fetuses manifested variable heart rate decelerations after the stimulation. In light of possible risks, the clinical use of the fetal acoustic stimulation test in labor should wait until its diagnostic value is better defined.