It is startling to know that every one in 1,000 babies born tested positive for permanent hearing loss in either single or pair of ears. The cases are prevalent in families with no background of hearing loss. The condition can affect the overall development of the baby. The babies are in a better position to develop their speech and language skills if detected at an early stage. Infant hearing screening is done immediately after the birth of a baby. Screening protocols have been implemented in the state and most diagnostic centres in Chennai conduct hearing tests before the baby is discharged from the hospital.
Nurses and paramedics are trained to conduct newborn ear screening using sophisticated equipment. The screening is repeated if the baby does not pass the first test; further tests are performed by specialists who have expertise and experience in the field. They are called audiologists and are trained with diagnostic hearing test techniques and rehabilitation for both children and adults.
Hearing loss has to be detected and treatment has to be initiated within first 6 months of the baby’s life. It gives a better chance of developing skills in relation to their peers while they enter into kindergarten. Children who are diagnosed of the condition at a later stage find it difficult to respond to the treatment, resulting in permanent and irreversible impairments in speech and cognitive skills.
Earlier only children with high risk of hearing loss were recommended for customary hearing screening tests. This includes
- Infant with family history of hearing loss
- Illness during pregnancy
- Exposure to drugs
- Low birth weight
- Oxygen deprivation
- High bilirubin levels
- Hearing loss syndromes
- Abnormality in head or face structures
- Born with infections like herpes, toxoplasmosis, syphilis or cytomegalovirus
- Low Apgar scores
Since a large group of infants are not identified with testing protocols, it becomes necessary to test for hearing loss before the baby leaves the hospital. It helps in improving their early years.
Aim of newborn hearing screening
Hearing screening is part of procedure in hospitals for newborns. The purpose is for two reasons, to identify if the child has hearing loss and offer further evaluation and the second is to verify babies with medical conditions leading to hearing loss at a later stage. The second situation will be a continuous process to prevent hearing loss at a later stage in the life of the child.
Initial hearing tests
Clearing the initial hearing tests does not mean the child is normal. In traditional hearing tests, the frequency specific hearing loss is tested. Infants with this condition clear the traditional screening. It is important to evaluate children for psychoeducational milestone during their childhood and opt for professional screening if there is a cause for concern.
There are certain instances where the newborn does not clear the initial screening even with normal hearing. There are a number of reasons attributed to this. Children failing initial hearing test are sent for a complete audiologic evaluation. Children with any hearing loss condition are diagnosed precisely within three months of age.
Types of infant hearing loss screening
There are two types of tested to evaluate hearing loss in infants; otoacoustic emission (OAE) or auditory brainstem response (ABR) measures. The tests are automated, accurate and noninvasive. Moreover, these tests do not require any evident response from the newborn. The tests depend on the program training and instrumentation. The screening tools used for each method is different. In some cases, the difference in hearing are measured placing ABR against OAE.
Auditory Brainstem Response or ABR in short, measures the response to sound in brainstem. The test is conducted with five electrodes, placing it on the head of the infant. Different sounds are presented to the infant using a earphone. The sound stimulated travels to the brain. This activity by the hearing nerve is recorded using the electrode and is displayed on the computer monitor. Different level of loudness is presented to check if the infant can listen to the softest levels. If the response is healthy, the infant has cleared the test. The test is completed within 15 minutes.
Otoacoustic emission test (OAE) is produced in the inner ear, it has to bounce out of the ear responding to the sound stimulus. The probe instruments used is a speaker and a microphone. These are placed inside the infant’s ears. Sounds are produced into the speaker. The inner ear processes the sound sending an electrical stimulus to the brainstem. Additionally a second sound that does not travel to the nerve is sent back to the ear canal of the infant. This is called otoacoustic emission. This emission is recorded using the microphone and is represented on the computer monitor in a graphic pattern. The audiologist will be able to determine the strength of the response. If the emission is vital to speech comprehension, the infant clears the test. The test can be completed within 8 minutes.