Fetal habituation to vibroacoustic stimulation in uncomplicated term pregnancies.

The use of transabdominal vibroacoustic stimulation has been shown to improve the efficiency of antepartum fetal surveillance. The ability of the fetus to habituate to such a stimulus has also been suggested as a means of assessing the function of the central nervous system. The purpose of this blinded prospective investigation was to evaluate fetal habituation in a group of low-risk pregnancies anticipated to deliver within 1 week. One hundred sixteen uncomplicated pregnancies underwent repetitive vibroacoustic stimulation using a Corometrics Model 146 fetal acoustic stimulator. Fetal habituation was defined as a sustained elevation of the heart rate baseline for more than 15 minutes or a failure to produce an adequate acceleration of the fetal heart rate after an initial response. Habituation was present in 106 (91.4%) cases, whereas 10 (8.6%) failed to habituate to the stimulus. All infants failing to habituate in utero ultimately did well after delivery. Their birthweights, Apgar scores, umbilical artery blood gas determinations, and courses in the newborn nursery were similar to those of infants who responded to in utero sound stimulation. However, cesarean delivery for fetal distress and gross placental abnormalities (such as infarction and abruption) occurred more commonly in those fetuses failing to habituate. Additional investigations of fetal habituation to a vibroacoustic stimulus may be helpful in the intrapartum risk assessment of uncomplicated term pregnancies.