Fetal vibroacoustic stimulation involves using an electronic hand-held device to transmit brief sound stimuli directly into a pregnant mother’s uterus in order to evoke responses from her baby that will detect distress or health problems during gestation.
Laborers use tests such as fetal movement counts and ultrasound examinations to monitor a baby’s wellbeing during labor, however some babies can become inactive during these examinations and additional efforts must be taken in order to awaken them.
What is Vibroacoustic Stimulation?
Vibroacoustic stimulation (VAS) is a non-invasive technique that employs sound and vibration to stimulate prenatal testing of an unborn fetus, usually during non-stress testing or biophysical profile assessments, or during high risk pregnancy management. VAS has been utilized safely since decades in helping doctors assess fetal health and activity.
VAS sessions involve low-frequency sound vibrations being passed from mother’s abdomen through the mother’s womb to the fetus, where low frequency sound vibrations cause low frequency sound vibrations to trigger what scientists believe to be a “startle response,” increasing heart rate and often leading to rapid contractions – an indicator of good health in many cases, though not all babies respond. Their response can then be monitored on a monitor, providing physicians with valuable insight into fetal health status.
Many maternity hospitals use VAS to encourage babies to move more during routine ultrasound assessments and preeclampsia monitoring. Fetuses are stimulated with short pulses of light or low-frequency sound and their heart rates should increase after moving – providing physicians with better information about fetuses’ movements and overall health, which helps determine whether intervention should occur in cases of premature labor.
Studies on the efficacy of fetal vibroacoustic stimulation have been undertaken in this context, with different results emerging from each trial. While some have found that it does indeed elicit startle responses in significant numbers of babies, others have noted this effect isn’t seen across all trials – this might be down to pregnancy stages being at different points and not all trials using stimulators with equal type or intensity levels.
Fetal vibroacoustic stimulation is being tested as an assessment method to monitor fetal well-being during labor. The goal is to ensure interventions such as cesarean delivery are reserved only when they truly need it; this could be particularly valuable in high-risk pregnancies. At present, tests such as counting the number of movements or heart rates of fetuses help identify babies likely needing intervention; however changes to these results during sleep periods make these assessments not always reliable.
Why is Vibroacoustic Stimulation used in pregnancy?
After showing a nonreassuring cardiotocograph trace (CTG), using Fetal Vibroacoustic Stimulation (VAS) can increase the effectiveness of antepartum Fetal Heart Rate Monitoring. As it’s noninvasive and simple, VAS allows interventions to only occur in cases which really warrant them; previous studies have also demonstrated its use to increase nonstress testing effectiveness while decreasing false positive rates.
VAS involves placing a small plastic device (either a stimulator or mock stimulus) on the maternal abdomen over the fetus and emitting vibration sound similar to what an electronic artificial larynx produces for several seconds, emitting vibration sound similar to electronic artificial larynx production, inducing startle reflex and speeding up of fetal heart rate acceleration; its changes may help predict when labor will begin.
Human fetuses can detect sounds through the bones of their inner ears, though low-frequency energy dominates most sounds available to it. Vowels can be detected, while consonants and musical overtones cannot. Furthermore, newborn humans show preference for melodies to which they were exposed prior to birth – suggesting a capacity for learning while in utero.
Attenuated noises or impulses may provoke abnormal responses in an unborn fetus, including abnormally excessive movements, long-lasting tachycardia, disorganization of behavioral states, and disruption of emotional states (Edersheim 1987; Smith 1986; Ingemarsson 1989). Studies have highlighted that stimulation intensity and duration play an integral part in its effectiveness as an outcome predictor.
At present, it remains unknown the optimal stimulation intensity and duration needed to produce an effect, though research suggests shorter stimuli are more effective than longer ones. Furthermore, type of stimulator used may influence results with some studies reporting more false negatives (Polzin 1988; Lin 2001). Randomised controlled trials must therefore be performed to establish efficacy of fetal VAS stimulation when compared to placebo or no stimulation.
How is Vibroacoustic Stimulation performed?
Fetal Vibroacoustic Stimulation (VAS) is an easy and noninvasive technique that uses sound waves emitted at predetermined levels for several seconds from a device on the mother’s abdomen over the region of fetal head, to produce startle reflexes in fetuses that should lead to movement as well as short acceleration or transient tachycardia in FHR responses which will provide assurance of their well-being.
VAS can assist in monitoring high-risk pregnancies. For instance, if the fetus fails to respond positively to routine NSTs in the third trimester, healthcare team may use VAS stimulation techniques in order to stimulate it into moving more often and increase chances of positive response – this allows doctors to accurately assess activity levels more precisely and assess if premature labor risk exists in each woman.
VAS can also be utilized as part of routine pregnancies at maternity hospitals, providing healthcare professionals with an assessment tool for how much the fetus is moving with an ultrasound examination using Doppler technology. If movement levels appear lacking, maternity nurses may use VAS stimulation techniques to stimulate and increase its activity levels.
Research has demonstrated that VAS can effectively decrease the number of unresponsive fetal heart rate tests during labor due to vibrations from low frequency sound waves stimulating the fetus to respond. This helps improve accuracy and decrease risks for both mother and child during this process.
Randomised controlled trials have examined the effects of fetal VAS with mock or no stimulation, with one or both being blind to treatment allocation by blinding investigators to the results of both. Mock stimulation involves placing the same device against the uterus as a VAS but without activating it; this prevents inadvertently altering sensitivity responses from stimuli that do not make contact. A number of these trials also included comparison between real and mock stimulation results to allow investigators to remain unaware of treatment allocation allocation.
What are the benefits of Vibroacoustic Stimulation?
Vibroacoustic stimulation (VAS) is a non-invasive prenatal diagnostic technique that uses sound and vibrations to elicit responses from the fetus during an antenatal non-stress test or biophysical profile assessment. VAS may help waken an inactive or sleeping baby during these assessments and improve accuracy, and is also an invaluable way to assess fetal health and well-being.
Vibroacoustic Stimulation (VAS) involves placing a small vibrating plate on the abdomen and playing low-frequency sound vibrations into the uterus, stimulating it with low frequency sounds that cause your heart rate to increase in response. Once this heart rate increase occurs, VAS records it and displays this data on a monitor so you can evaluate it against past records to assess your fetus’ health and well-being.
All the included trials employed a randomisation scheme to assign women either to vibroacoustic stimulation groups or control groups, though four trials left unclear how they concealed allocation, while blinding was never mentioned at any point during one of them.
Six of the twelve studies revealed that fetal vibroacoustic stimulation was linked to reduced instances of non-reactive cardiotocography tests (9 trials, risk ratio 0.62, 95% confidence interval 0.42 to 0.81) and shorter testing times for modified biophysical profiles. Two trials specifically reported on perinatal outcomes; these found that women receiving vibroacoustic stimulation had lower rates of fetal distress than those not (one trial, relative risk = 0.084, 95% CI:0.1 to 1.0).
It is likely that different intensities and durations of stimulation used across trials contributed to the results observed, as well as how positioning of the stimulator played a part in different results seen. For instance, both Polzin 1988 and Lin 2001 reported false negative results when placed near a fetus’ mouth while Edersheim 1987 and Smith 1986 did not see this problem. Therefore further research needs to identify optimal intensity, frequency and durations of acoustic stimulation to minimize false positive non-reactive test results.
