Buzz
According to research, out of approximately 1000 newborns, 2-3 infants may experience hearing impairment. Poor hearing can impact a child's ability to hear and speak. This is why many scientists worldwide recommend determining a child's hearing ability and providing intervention before the age of 6 months.
Early detection and timely treatment can result in infants developing skills nearly equivalent to those of normal children. For infants identified too late (at 2-3 years or later), they may endure permanent disabilities, affecting language development, cognition, and pronunciation, unlike their normal peers.
This underscores the crucial nature of screening for hearing loss in newborns immediately after birth, a practice parents should advocate for. Nowadays, hospitals often inquire about the screening at birth. Doctors will conduct tests, and if the baby passes the first time, their hearing ability is considered normal. If not, further testing and consultation with a specialized hearing expert may be recommended.
I. Factors Contributing to Hearing Loss in Children
– Almost all cases of permanent hearing loss result from the destruction or dysfunction of the auditory nerve transmitting sound signals from the inner ear to the brain. However, only about half of these cases have identifiable causes. Among the determinable causes, approximately half occur during pregnancy and childbirth, while the remaining half are attributed to genetic factors.
Factors contributing to a higher risk of hearing loss in some children include:
- Children born to mothers with certain pregnancy-related illnesses such as cytomegalovirus, rubella (German measles), syphilis, herpes, toxoplasmosis (cat scratch disease)...
- Family history of hearing loss.
- Mothers using medications such as potent antibiotics for bacterial infections belonging to the aminoglycosides class (gentamycin, kanamycin), cancer chemotherapy, or exposure to hazardous chemicals that can affect hearing.
- Premature, low birth weight, or infants showing signs of respiratory distress after birth requiring prolonged ventilator support.
- Infants with jaundice due to elevated bilirubin levels, or meningitis.
- Infants with low Apgar scores after birth.
- Children with abnormal head, face, outer ear, and middle ear structures.
Aside from the mentioned cases, even infants without these risk factors may still be at risk of hearing loss. Therefore, screening programs should be applied to all newborns before they leave the hospital.
II. Two Methods for Screening Hearing Loss in Newborns
Currently, two main methods are employed worldwide for hearing screening in infants:
– Measuring sound from the ear canal (otoacoustic emission – OAE)
– Assessing the brainstem's response to sound (auditory brainstem response – ABR).
The main advantages of both methods lie in their high accuracy, non-invasiveness, painless for the child, automatic operation, and requiring no subjective observation of the child's response.
1. Otoacoustic Emission (OAE) Method
The OAE method measures the response in the ear when stimulated by sound. This test typically lasts 5-8 minutes and is conducted as follows:
– The examiner places a probe containing a small microphone and speaker into the infant's ear. When the infant lies quietly, very soft sounds are emitted from the probe.
– When the ear receives the sound, the signal travels to the brain. Additionally, a separate sound reflects back from the ear canal. This sound is known as the 'emitted' sound from the ear.
– The 'emitted' sound is recorded through the microphone and displayed on the screen. The examiner can identify which sounds generate the 'emitted' response and the magnitude of the response.
– If there is an 'emitted' response for the most crucial sounds for future speech development at an allowable level, the child is considered to have passed the test.
2. Auditory Brainstem Response (ABR) Assessment
The ABR method is a physical measurement, assessing electrical impulses from the ear to the brain in response to sound. This screening method measures the overall connection of the hearing system from the ear to the brain.
– The examiner will place 4-5 electrodes on the infant's head, and the child will listen to various sounds through a small earphone. Sound stimuli are transmitted to the brain, and the electrodes record them as waves on the screen.
– The examiner can adjust the volume of different sounds and determine the softest level the infant can hear.
– For screening purposes, the examiner may use a single sound, such as a small clicking noise. If there are signs of a response, the infant is considered to have passed the test.
– Typically, the test lasts about 5-10 minutes.
Differences between the Two Methods
– OAE measurement method is generally simpler and less expensive. However, its false positive rate (normal hearing but fails the test) is higher compared to ABR when conducted within the first 3 days after birth.
– This difference is due to the OAE method being more sensitive to amniotic fluid or debris commonly found in infants' ears. Many screening programs use OAE first, followed by ABR for infants who do not pass the OAE test.
These two testing methods differ in mechanisms, and therefore, using a combination of both methods provides a better assessment of the child's hearing ability.
III. What does it mean if the child does not pass the test?
– Not all infants failing the hearing test necessarily have hearing loss. Statistics show that approximately 2-10% of newborns in the United States do not pass the initial hearing test. There are various reasons to consider. Firstly, there may be fluid in the ear canal, hindering sound stimuli from reaching the inner ear. Similarly, fluid accumulation in the middle ear, behind the eardrum, can also impede sound stimuli, leading to false positive results. Therefore, if an infant doesn't pass the test, it's necessary to wait at least one week for the baby's ear to dry before retesting. Another reason could be external noise being too loud, the baby crying, or the baby moving during the test. Hence, the child needs to be calm or asleep during the test. Feeding the baby before the test often makes them sleep more easily.
– If there is clear evidence of hearing loss through these tests, the child needs to be referred to hearing specialists for a comprehensive diagnosis of the type and degree of hearing loss. Specialists will conduct more specific and precise measurements to determine whether the impairment is permanent or treatable. Usually, the ABR technique with various sound stimuli is applied.
– In summary, when a newborn fails the initial hearing test at the hospital after birth, doctors may recommend a revisit to the ear, nose, and throat center for retesting after a week. If the child continues to fail the second test, more advanced diagnostic tests will be conducted. If diagnosed with hearing loss, the audiologist will specify the type and degree of the condition. For instance, hearing loss due to physical issues like middle ear inflammation, fluid buildup, eardrum perforation, or abnormal ear structures can be treated with medication or surgery. Hearing loss due to neurological reasons is more complex, requiring hearing aids or cochlear implants.
Children with hearing loss face numerous challenges not only in communication, speech, and language but also an increased risk of behavioral disorders and difficulties in education. Therefore, early detection and timely intervention are crucial for the child's optimal development, ensuring they thrive like their normal peers.
(Compiled)
