Hearing impairment is the decreased ability to hear and discriminate among sounds. It is one of the most common birth defects. Each year in the United States, about 12,000 babies (3 in 1,000) are born with significant hearing impairment (1). Hearing impairment that is present at birth is called congenital hearing impairment. Hearing impairment also can develop later in childhood or during adulthood.
The Centers for Disease Control and Prevention (CDC) recommends that all babies be screened for hearing impairment before 1 month of age, preferably before they leave the hospital (1). This is because language and communication develop rapidly during the first two to three years of life, and undetected hearing impairment can lead to delays in developing these skills. Without newborn screening, children with hearing impairment usually are not diagnosed until 2 to 3 years of age (1).
The goal of early screening, diagnosis and treatment is to help children with hearing impairment develop language and academic skills equal to those of their peers. Most states have an Early Hearing Detection and Intervention Program to help ensure that all babies are screened, and that infants who do not pass the screening receive the follow-up care they need. The March of Dimes, the American Academy of Pediatrics, the Maternal and Child Health Bureau, the CDC and others strongly support these programs.
What causes hearing impairment in babies and children?
Hearing impairment can be inherited (genetic) or nongenetic. Nongenetic causes include illness or injury occurring before, during or after birth. In some cases, the cause of hearing impairment is not known. About 90 percent of babies with congenital hearing impairment are born to hearing parents (1).
Genetic factors are believed to cause 33 percent of cases of hearing impairment in infants and young children (1). Scientists believe that mutations (changes) in as many as 400 genes may contribute to hearing impairment (1).
Genetic causes (1) of hearing impairment can be:
- Syndromatic: One feature of a group of birth defects that occur together. This type of impairment accounts for about 30 percent of cases.
- Nonsyndromatic: A solitary birth defect. About 30 percent of cases of nonsyndromatic hearing impairment are caused by a mutation in a gene called Connexin 26.
About one-third of cases of hearing impairment are caused by nongenetic factors (1). They include illnesses during pregnancy, such as:
After birth, head injuries and childhood infections (such as meningitis, measles or chickenpox) can cause permanent hearing impairment. Certain medications, such as the antibiotic streptomycin and related drugs, also can cause hearing impairment. Ear infection (otitis media) may cause temporary hearing impairment. Frequent and poorly treated ear infections can cause damage sufficient to impair hearing.
The causes of the remaining third of cases of hearing impairment in infants and children are unknown (1).
Are there different types of hearing impairment?
Yes. When sound enters the outer ear (auricle or pinna), it moves through the ear canal to the eardrum (tympanic membrane). Incoming sound causes the eardrum to vibrate, which moves three small bones (ossicles) in the middle ear. In this way, the ear canal, the eardrum and the middle ear transmit sound from the outside to the inner ear (cochlea). Within the inner ear, thousands of tiny hair cells detect the incoming vibrations and convert them into signals that are relayed to the auditory nerves, which send neural impulses to the hearing center in the brain.
Hearing impairment can occur in different parts of the hearing pathway.
- Conductive hearing impairment occurs when something interferes with sound passing through the outer or middle ear. A blockage in the ear canal, damage to the eardrum, and fluid or an infection in the middle ear (called otitis media) are examples of conditions that can cause conductive hearing impairment. This type of hearing impairment is usually temporary and often can be corrected with medication or drainage.
- Sensorineural hearing loss occurs when the hair cells in the inner ear cannot detect all incoming vibrations or when neural impulses are not transmitted to the brain. Prenatal infections or genetic factors can cause this type of hearing impairment. Sensorineural hearing impairment is generally permanent. However, many children can be helped with devices that amplify sound. Sensorineural hearing impairment also can result from damage to the brain's auditory center.
- Mixed hearing impairment occurs when a child who has a sensorineural hearing impairment also has a conductive impairment (such as fluid in the middle ear). Early and proper treatment of acute ear infections is crucial to protecting children from hearing impairment.
How are newborns screened for hearing impairment?Newborns are screened for hearing impairment with one of two tests. Both tests measure how a baby responds to sound. The tests take five to 10 minutes, are painless and can be done when the baby is sleeping.
In the otoacoustic emissions (OAE) test, a small microphone is placed in the baby's ear. The microphone, connected to a computer, sends soft clicking sounds or tones into the ear and records the inner ear's response to sound.
In the automated auditory brainstem response (AABR) test, soft clicking sounds are presented to the ear through small earphones. Sensors placed on the head and connected to a computer measure brain wave activity in response to sound.
What happens if a baby does not pass the hearing screening?
If a baby does not pass the OAE or the AABR:
- The test should be repeated or
- The baby should be referred either to a hearing specialist (audiologist) or to an ear, nose and throat (ENT) specialist (also called an otolaryngologist). The specialist will do more extensive tests to determine if the baby has a hearing impairment.
It is important for babies to be assessed by specialists who have experience testing very young children. Diagnostic testing should be completed by the time a baby is 3 months old (1).
The screening tests are only a general indication that there may be a problem. While up to 10 percent of babies have abnormal results on their hearing screening test, some will be found normal on additional tests (1).
What tests are used to diagnose hearing impairment after the newborn period?
The most common hearing test for infants under 6 months of age is the diagnostic auditory brainstem response test. It is similar to the automated AABR, but it provides more information and must be administered by a specialist.
Children between 6 months and 2 years of age often are tested with visual reinforcement audiometry (VRA). During VRA testing, a series of sounds are presented to the child through earphones or speakers. The child is trained to turn toward any sound and is rewarded with an entertaining visual image for responding.
Children between 2 and 4 years of age are tested with conditioned play audiometry (CPA). Children are asked to perform a simple play activity (like placing a ring on a peg) when they hear a sound. This is similar to the test for older children and adults who press a button or raise their hand when they hear a sound.
These tests also may be recommended:
- If a child was not screened as a newborn
- If a child has had persistent ear infections, meningitis or other illness that can cause hearing loss
- If a child has been diagnosed with a syndrome that can include hearing loss
- If a parent suspects the child is not responding normally to sounds
What are some signs of hearing impairment in infants and young children?Parents should be alert to any signs of hearing impairment and discuss them with their child's health care provider. Some signs include:
- Failure to startle at loud sounds
- Not turning toward the sound of a voice or imitating sounds after about 6 months of age
- Lack of babbling at 9 months of age
- Not using single words by 18 months of age
- Using gestures instead of words to express needs
Parents should be concerned about hearing impairment in older children if they:
- Develop vocabulary more slowly than their peers
- Have speech that is difficult to understand or that is too loud or too soft
- Often ask for words to be repeated
- Turn on the TV too loud
- Appear inattentive at school and have difficulties learning to read or perform simple mathematics
How is hearing impairment treated?
A child with a congenital hearing impairment should begin receiving treatment before 6 months of age (1). Studies suggest that children treated this early usually are able to develop communication skills (using spoken or sign language) that are as good as those of hearing peers (2, 3).
Because of the Individuals with Disabilities Education Act, children with a hearing impairment between birth and 3 years of age have the right to receive interdisciplinary assessment and early intervention services at little or no cost. After age 3, early intervention and special education programs are provided through the public school system.
There are a number of treatment options available, and parents need to decide which are most appropriate for their child. They should consider the child's age, developmental level and personality, and the severity of the hearing impairment. Ideally, a team of experts, including the child's primary care provider, an otolaryngologist, a speech-language pathologist, an audiologist and an educator, work closely with the parents to create an Individualized Family Service Plan. Treatment plans can be changed as the child gets older.
Children as young as 4 weeks of age can benefit from a hearing aid (2, 4). These devices amplify sound, making it possible for many children to hear spoken words and develop language. However, hearing aids help some children with hearing impairment more than others. Some children with severe to profound hearing impairment may not be able to hear enough sound, even with a hearing aid, to make speech audible. A behind-the-ear hearing aid often is recommended for young children because it is safer and more easily fitted and adjusted as the child grows, as compared to one that fits within the ear.
Parents also need to decide how their family and child are going to communicate. If the child is going to communicate orally (speech), she may need help to learn listening and lip-reading skills. Many children with hearing impairment also need some type of speech or language therapy.
A child also can learn to communicate using a sign language. A widely used type of sign language is American Sign Language (ASL), which has rules and grammar that are distinct from English. There also are several variations of sign language that can be used along with spoken English.
Surgery may be recommended if a child has a permanent conductive hearing impairment caused either by malformations of the outer or middle ear or by repeated ear infections. Although fluid in the middle ear usually results in only temporary hearing loss, chronic ear infection can cause a child to fall behind in language skills. In some cases, a provider may suggest inserting a tube through the eardrum to allow the middle ear to drain. This procedure generally does not require an overnight hospital stay.
Surgery may be an option for some children with severe to profound sensorineural hearing loss. A device called a cochlear implant can be surgically inserted in the inner ear of children as young as 12 months of age to stimulate hearing. The surgery sometimes requires an overnight hospital stay. With additional language and speech therapy, children with cochlear implants may learn to understand speech and speak reasonably well, but the amount of improvement is variable.
A 2003 study found that bacterial meningitis occurred more often in children with cochlear implants than in other children of the same age (5). Parents of children with cochlear implants should be aware of the symptoms of meningitis (high fever, headache, stiff neck, nausea, discomfort looking into bright lights, sleepiness and confusion) and report them to the child's health care provider immediately (1).
Does the March of Dimes support research on hearing impairment?
Several March of Dimes grantees are exploring the role that specific genes play in causing hearing impairment, with the ultimate goal of developing new treatments for hereditary hearing impairment. Others are seeking to prevent hearing impairment by preventing infections (such as cytomegalovirus) that can cause it and to improve treatment of individuals with hearing impairment. One is evaluating deaf children's difficulty in learning to spell and read in order to develop improved educational programs.
For more information
References
- Centers for Disease Control and Prevention (CDC). Early Hearing Detection & Intervention Program. May 9, 2007.
- American Speech-Language-Hearing Association. Hearing Disorders. Accessed 6/7/07.
- American Academy of Pediatrics (AAP). Hearing-Understanding Screening Results. Accessed 6/8/07.
- National Center for Hearing Assessment and Management (NCHAM). Universal Newborn Hearing Screening. Utah State University, Logan, UT, accessed 6/7/07.
- Reefhuis, J., et al. Risk of Bacterial Meningitis in Children with Cochlear Implants. New England Journal of Medicine, volume 349, number 5, July 31, 2003, pages 435-445.
August 2007
