Birth defects

• Birth defects can cause disabilities and even death.
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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 some degree of 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 after birth (1). This is because language and communication develop rapidly during the first 2 to 3 years of life, and undetected hearing impairment can lead to delays in developing these skills. Without newborn screening, children with hearing impairment often 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 (AAP), the CDC and others strongly support these programs.

What causes hearing impairment in babies and children?
Hearing impairment can be genetic (inherited) or non-genetic. Non-genetic causes include illness or injury 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 parents with normal hearing (1, 2).

Genetic factors are believed to cause 50 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, 3).

Genetic causes of hearing impairment can be:

• Syndromatic: Syndromatic means that the hearing impairment happens with a specific group of birth defects. It’s not the only birth defect a baby has. This type of hearing impairment accounts for about 30 percent of genetic cases (1, 3).
• Non-syndromatic: Non-syndromatic means that hearing impairment is the only birth defect a baby has. About 50 percent of cases of non-syndromatic genetic hearing impairment are caused by a mutation in a gene called connexin 26 (3).

About 25 percent of cases of hearing impairment are caused by non-genetic factors (1). These include premature birth (before 37 completed weeks of pregnancy) and illnesses during pregnancy, such as:

• Rubella (German measles)
• Cytomegalovirus infections
• Toxoplasmosis 
• Herpes infection 
• Syphilis 

Non-genetic causes of hearing impairment after birth include:

• Head injuries
• Childhood infections (such as meningitis, measles or chickenpox)
• Certain medications (such as the antibiotic streptomycin and related drugs)
• Ear infections (otitis media) – These usually cause temporary hearing impairment. However, frequent and poorly treated ear infections can cause permanent hearing impairment.

The causes of the remaining 25 percent 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 (called either 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 (otitis media) are examples of conditions that can cause conductive hearing impairment. This type of hearing impairment usually is temporary and often can be corrected with medication or draining fluid out of the ear.
• Sensorineural hearing impairment 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 generally is permanent. However, many children can be helped with hearing aids that amplify sound. Sensorineural hearing impairment also can result from damage to the brain’s hearing center.
• Mixed hearing impairment occurs when a child has both a conductive impairment and a sensorineural impairment. Early and proper treatment of acute ear infections is crucial to protecting children from additional 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 5 to 10 minutes, are painless and can be done when the baby is sleeping.

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.
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 to a hearing specialist (audiologist) or an ear, nose and throat (ENT) specialist (otolaryngologist). The specialist does more extensive tests (diagnostic tests) to determine if the baby has a hearing impairment.

It is important for babies who don’t pass the screening 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 of age (1, 4).

Screening tests cannot diagnose hearing impairment; they only indicate that there may be a problem. Up to 10 percent of babies have abnormal results on their hearing screening test (1). Diagnostic tests show that most of these babies do not have hearing impairment.

What tests are used to diagnose hearing impairment?
The most common diagnostic hearing test for infants under 6 months of age is the diagnostic auditory brainstem response test (2). It is similar to the AABR, but it provides more information and must be given by a specialist.

Tests used to diagnose hearing impairment in older infants and children include (2):

• Visual reinforcement audiometry (VRA): This test is used in children between 6 months and 2½ years of age. In VRA testing, a series of sounds are presented to the child through earphones or speakers. The child is asked to turn toward any sound and is rewarded with an entertaining visual image for responding.
• Conditioned play audiometry (CPA): In CPA, children between 2½ and 4 years of age are asked to perform a simple play activity (like placing a ring on a peg) when they hear a sound.
• Conventional audiometry: Children ages 4 years and older are asked to press a button or raise their hand when they hear a sound.

The AAP recommends that children with a risk factor for hearing impairment have one of these diagnostic tests by 2 to 2½ years of age, even if they pass the newborn screening test (2).

What are some risk factors for hearing impairment?
Children who have one of these risk factors should have a diagnostic hearing test (2):

• The parent suspects that the child is not responding normally to sounds.
• The child has had persistent ear infections, meningitis or other illness that can cause hearing impairment.
• The child was infected before birth with cytomegalovirus or certain other infections.
• The child has been diagnosed with a syndrome that can include hearing impairment.
• The child has certain craniofacial (defects of skull and face) abnormalities, including ear abnormalities.
• There is a family history of permanent childhood hearing impairment.
• The child was treated in the NICU (newborn intensive care unit) for more than 5 days or was treated with certain medications.
• The child suffered a head injury.

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 by 12 months of age
• Failure to respond to name by 12 months of age
• Not using single words by 18 months of age
• Failure to follow simple directions by 18 months of age

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 trouble learning to read or perform simple mathematics.

How is hearing impairment treated?
A child with 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 (4).

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 early intervention services at little or no cost. The public school system provides early intervention and special education programs for children after age 3.

A number of treatment options are 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 health care provider, an otolaryngologist, a speech-language specialist, an audiologist and one of the child’s teachers, work closely with the parents to create an individualized family service plan. This treatment plan can be changed as the child gets older.

Children as young as 4 weeks of age can benefit from a hearing aid (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 be able to hear speech. Providers often recommend a behind-the-ear hearing aid for young children because it is safer and more easily fitted and adjusted as the child grows, as compared to one that fits inside the ear.

Parents also need to decide how their family and child are going to communicate. If the child is going to communicate with speech, she may need help with 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.

When is surgery recommended?
Health care providers may recommend surgery if a child has a permanent conductive hearing impairment caused by malformations of the outer or middle ear, or by repeated ear infections. Although fluid in the middle ear usually causes temporary hearing loss, chronic (long-lasting or frequent) 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.

What is a cochlear implant?
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 children as young as 12 months of age to stimulate hearing (5). One part of the device sits behind the ear. The second part is surgically placed under the skin and inside the skull, with wires threaded into the inner ear. The surgery sometimes requires an overnight hospital stay. With 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, although rare, occurred more often in children with cochlear implants than in other children of the same age (6). 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). Parents should also make sure their child’s vaccinations are up to date, including the pneumococcal and haemophilus vaccines that help protect against meningitis.

What other conditions are common in children with hearing impairment?
At least one-third of children with hearing impairment have other conditions, including vision problems, learning disabilities, attention problems and autism (2). The child’s health care provider usually screens for these conditions during regular well-child visits. However, parents should always discuss any concerns about their child’s development with his health care provider.

Does the March of Dimes support research on hearing impairment?
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 genetic hearing impairment. Several grantees are seeking to prevent hearing impairment by preventing prenatal infections (such as cytomegalovirus and toxoplasmosis) that can cause it. Others are seeking to improve diagnosis and treatment of individuals with hearing impairment. One is evaluating deaf children’s difficulty learning to spell and read in order to develop improved education programs. Another is seeking to increase the accuracy and efficiency of diagnosing hearing impairment during the first year of life.

For more information

• The CDC’s Early Hearing Detection and Intervention Program (EHDI) provides educational materials for families and health care providers.
• The National Center for Hearing Assessment and Management (NCHAM) provides resources for health care providers and families. The center has produced a 6-minute video for parents, “Sound Beginnings,” in English and Spanish. Parents can view the video online at no charge, or they can buy a copy.
• The Alexander Graham Bell Association for the Deaf and Hard of Hearing helps families, health care providers and education professionals understand childhood hearing loss and the importance of early diagnosis and intervention.

References

1. Centers for Disease Control and Prevention (CDC). (2009). Early Hearing Detection & Intervention Program. Retrieved October 1, 2009.
2. American Academy of Pediatrics (AAP). (2009). Clinical Report–Hearing Assessment in Infants and Children: Recommendations Beyond Neonatal Screening. Pediatrics, 124(4), 1252-1263.
3. Smith, R. & Van Camp, G. (2008). Deafness and Hereditary Hearing Loss Overview. GeneReviews. Retrieved October 1, 2009.
4. American Speech-Language-Hearing Association. (2009). Children and Hearing Aids. Retrieved October 2, 2009.
5. National Institute on Deafness and Other Communication Disorders. (2009). Cochlear Implants. Retrieved October 1, 2009.
6. Reefhuis, J., Honein, M.A., Whitney, C.G., Chamany, S., Mann, E.A., et al. (2003). Risk of Bacterial Meningitis in Children with Cochlear Implants. New England Journal of Medicine, 349(5), 435-445.

March 2010