Methods
Sound vibrations travel through a fetal uterus until they reach its inner ears, where sound-receiving hair cells that act like delicate antennae of its hearing system dance to their rhythm and convert that movement into electrical signals recorded by electrodes near its eyes (ocular vestibular evoked myogenic potential, or oVEMP). This response tells us a great deal about whether the fetus is experiencing healthy sleep cycles or potentially dangerous hypoxic distress.
Vibroacoustic stimulation has proven itself an effective means to diagnose miscarriage by stimulating a startle response that induces heart rate accelerations. Otology uses it similarly, using vibration stimuli to detect Superior Semicircular Canal Dehiscence – an uncommon but serious inner ear condition characterized by pathologically amplified vibration responses – through observation.
Fetal vibroacoustic stimulation works using an electronic hand-held device placed over a pregnant mother’s abdomen. A clinician then sends brief sound waves directly into the fetus’ auditory system for less than one minute of stimulation exposure.
This method is safe and quick – providing clinicians with direct answers in minutes from asking a question to providing feedback about fetal wellbeing. It can be used alongside more cumbersome tests of fetal wellbeing such as sugary drinks or caffeine to quickly gather data for assessment purposes.
One essential aspect to keep in mind when providing intrapartum care is that many medications given to mothers for pain relief or medical conditions such as preeclampsia (such as magnesium sulfate) may cross the placenta and disrupt nerve activity, making it harder to elicit VAS responses; disentangling their effects from true fetal distress remains one of the greatest obstacles of intrapartum care.
Results
Fetal vibroacoustic stimulation significantly improves fetal wellbeing tests by decreasing false positive results, as demonstrated in a meta-analysis involving 12 randomised controlled trials with 6822 women participating. Acoustic stimulation is safe and may improve preterm heart rate testing during gestation.
Two or more fetal heart rate accelerations within 20 minutes is considered a non-stress test that should provide comfort. Fetal vibroacoustic stimulation arouses the unborn baby into an awake state and triggers these reassuring movements and associated heart rate accelerations, helping reduce false positive rates without increasing false negative rates.
Current trial: We are conducting a randomized, controlled, single blinded trial to compare the frequency with which one or more fetal heart rate accelerations occur in 15 minutes following vibroacoustic stimulation with Corometrics Model 146 Fetal Acoustic Stimulator vs the custom mobile app designed specifically for this research study using vibration to arouse and induce similar responses as found with handheld device.
