Home   Hearing Information

Hearing Information

Hearing is a vital part of a child’s social, emotional, and cognitive development from a very young age. Just a mild hearing loss can affect a child's ability to speak and understand language, which in turn affects the child’s learning once they reach a school going age.  Hearing problems can however be treated if they're caught early — it is best to have caught the hearing loss by the time a baby is 3 months old. It is therefore important to get your child's hearing screened early and evaluated regularly, at least once a year until they are in Grade 3 and then if there are any reasons for concern thereafter. 

Causes of Hearing Loss
Hearing loss is a common birth defect, affecting about 1 to 3 out of every 1,000 babies. (These statistics are based on World Wide Statistics as we have not done accurate statistics in Zimbabwe.) A number of factors can lead to hearing loss, and about half the time, no cause is found.

Hearing loss can occur if a child:

  • was born prematurely
  • stayed in the neonatal intensive care unit
  • had high bilirubin requiring a transfusion
  • was given medications that can lead to hearing loss
  • has a family history of childhood hearing loss
  • had complications at birth
  • had frequent ear infections; had infections such as meningitis or cytomegalovirus
  • exposed to very loud sounds or noises even of brief duration

When Should Hearing Be Evaluated?
Most children who are born with a hearing loss can be diagnosed through a hearing screening. But in some cases, the hearing loss is caused by things like infections, trauma, and damaging noise levels, and the problem doesn't emerge until later in childhood. So it's important to have children’s hearing evaluated regularly as they grow.

In the developed world your newborn will likely have a hearing screening before being discharged from the hospital. If your baby doesn't have this screening, or was born at home or a birthing center, it's important to have a hearing screening within the first 6 weeks of life. We like to recommend that the screening is done once the mother is comfortable and has had a chance to bond with her baby, but within the first 6 weeks.

If your baby does not pass the hearing screening, it doesn't necessarily mean there's a hearing loss. Because debris or fluid in the ear can interfere with the test, it's often redone to confirm a diagnosis.

If your newborn doesn't pass the initial hearing screening, it's important to get a retest in order to start treatment right away. Treatment for hearing loss can be the most effective if it's started by the time a child is 6 months old.

Kids who seem to have normal hearing should continue to have their hearing evaluated at regular appointments.

But if your child seems to have trouble hearing, if speech development seems abnormal, or if your child's speech is difficult to understand, talk with your doctor/ audiologist.

Symptoms of a Hearing Loss
Even if your newborn passes the hearing screening, continue to watch for signs that hearing is normal.  Some hearing milestones your child should reach in the first year of life:

  • Most newborn infants startle or "jump" to sudden loud noises.
  • By 3 months, a baby usually recognizes a parent's voice.
  • By 6 months, an infant can usually turn his or her eyes or head toward a sound.
  • By 12 months, a child can usually imitate some sounds and produce a few words, such as "Mama" or "bye-bye."

As your baby grows into a toddler, signs of a hearing loss may include:

  • limited, poor, or no speech
  • frequently inattentive
  • difficulty learning
  • often increases the volume on the TV
  • fails to respond to conversation-level speech or answers inappropriately to speech

Types of Hearing Loss
Conductive hearing loss is caused by an interference in the transmission of sound to the inner ear. Infants and young children frequently develop conductive hearing loss due to ear infections. This loss is usually mild, temporary, and treatable with medicine or surgery.

Sensorineural hearing loss involves malformation, dysfunction, or damage to the inner ear (cochlea) and is rarely due to problems with the auditory cortex of the brain. The most common type is cochlear hearing loss and this may involve a specific part of the cochlea (inner hair cells or outer hair cells or both). It usually exists at birth. It may be hereditary or may be caused by a number of medical problems, but sometimes the cause is unknown. This type of hearing loss is usually permanent.

The degree of sensorineural hearing loss can be mild, moderate, severe, or profound. Sometimes the loss is progressive (hearing gradually becomes poorer) and sometimes unilateral (one ear only).

Because the hearing loss may be progressive, repeat audiologic testing should be done. Sensorineural hearing loss is generally not reversible medically or surgically, but children with this type of hearing loss often can be helped with hearing aids.

A mixed hearing loss occurs when both conductive and sensorineural hearing loss are present.

A central hearing loss involves the hearing areas of the brain, which may show as difficulty "processing" speech and other auditory information. This is often referred to as "auditory processing disorder" and may be misdiagnosed as a behavioral disorder.

How Hearing Is Tested
Several methods can be used to test a child's hearing, depending on the child's age, development, or health status.

Behavioral tests involve careful observation of a child's behavioral response to sounds like calibrated speech and pure tones. Pure tones are the distinct pitches (frequencies) of sounds. Sometimes other calibrated signals are used to obtain frequency information.

The behavioral response might be an infant's eye movements, a head-turn by a toddler, placement of a game piece by a preschooler, or a hand-raise by a gradeschooler. Speech responses may involve picture identification of a word or repeating words at soft or comfortable levels. Very young children are capable of a number of behavioral tests.

Physiologic Tests
Physiologic tests are not hearing tests but are measures that can partially estimate hearing function. They're used for kids who can't be tested behaviorally (due to young age, developmental delay, or other medical conditions) and sometimes can help find which function of the auditory system is at fault.

Auditory brainstem response (ABR) test
For this test, tiny earphones are placed in the ear canals and small electrodes (which look like small stickers) are placed behind the ears and on the forehead. Usually, click-type sounds are introduced through the earphones, and the electrodes measure the hearing nerve's response to the sounds. A computer averages these responses and displays waveforms. An infant may be sleeping naturally or may have to be sedated for this test. Older cooperative kids may be tested in a silent environment while they're visually occupied.

Because there are characteristic waveforms for normal hearing in portions of the speech range, a normal ABR can predict fairly well that a baby's hearing is normal in that part of the range. An abnormal ABR may be due to hearing loss, but it may also be due to some medical problems or measurement difficulties.

Auditory steady state response (ASSR) test
An infant is typically sleeping or sedated for the ASSR. This is a new test that currently must be done in conjunction with the ABR to assess hearing. Sound is transmitted through the ear canals, and a computer picks up the brain's response to the sound and automatically establishes the hearing level. This test is still under development.

Otoacoustic emissions (OAE) test
This brief test is performed with a sleeping infant or an older child who may be able to sit quietly. A tiny probe is placed in the ear canal, then many pulse-type sounds are introduced and an "echo" response from the outer hair cells in the inner ear is recorded. These recordings are averaged by a computer. A normal recording is associated with healthy outer hair cell function and reflects normal hearing, although in some cases the hearing loss may be due to problems in other parts of the hearing pathway.

ABR or OAE tests are used at hospitals to screen newborns. If a baby fails a screening, the test is usually repeated. If the screening is failed again, the baby is referred for full hearing evaluation.

Tympanometry
Tympanometry is not a hearing test but a procedure that can show how well the eardrum moves when a soft sound and air pressure are introduced in the ear canal. It's helpful in identifying middle ear problems, such as fluid collecting behind the eardrum.

A tympanogram is a graphic representation of tympanometry. A "flat" line on a tympanogram may indicate that the eardrum is not mobile, while a "peaked" pattern often indicates normal function.

Who Performs Diagnostic Hearing Tests?
A pediatric audiologist specializes in evaluating and assisting kids with hearing loss and works closely with doctors, educators, and speech/language pathologists.

Treatment for Hearing Loss
Hearing aids are the primary nonmedical treatment for hearing loss. The most common type of hearing loss involves outer hair cell dysfunction; hearing aids allow an amplification of sound to overcome this problem. A hearing aid's basic components are the microphone, amplifier, and receiver. A number of circuit options modify how the hearing aid makes certain sounds louder.

There are several hearing aid styles; some are worn on the body while others fit behind the ear or in the ear. Some specialized hearing aids are attached to the bone of the skull to send sound waves directly to the cochlea and may be used in conditions of conductive hearing loss not amenable to standard hearing aids. No single style or manufacturer is best — hearing aid selection is based on a child's individual needs. Most kids with bilateral hearing loss (both ears) wear two hearing aids.

Hearing aids are expensive due to their sophisticated technology, and cost at least several hundred dollars. Unfortunately, they're often not covered by health insurance companies.

A specialized amplification device called an FM system may help in school. FM systems are sometimes called "auditory trainers." They may be provided in the classroom to improve hearing in group or noisy environments and also can be fitted for personal or home use. Other assistive listening or alerting devices may help older kids.

In addition to hearing aids or FM systems, hearing rehabilitation may include auditory or listening therapy and speech (lip) reading.

A cochlear implant does not restore hearing but rather transmits sound information past the damaged cochlea directly to the nerve of hearing. It is intended for children with profound hearing loss who do not benefit from hearing aids.

Reviewed by: Thierry Morlet, PhD Date reviewed: October 2009