Congenital Hearing Loss and Infant Hearing Screening
Testing your Newborn’s Hearing
Having your newborn’s hearing tested before they leave the hospital is not only a good idea – in many cases it is mandatory. Many states require all newborns to be tested within the first two months of birth, but regulations vary from state to state.
The tests are simple and painless. It is very important to know if an infant has any hearing loss, because early detection and treatment can mean the difference between normal and delayed development.
The two most common tests are Otoacoustic Emissions (OAE) and Auditory Brainstem Response (ABR). Otoacoustic Emissions (OAEs) test the baby’s hearing by placing a small microphone and earphone in the ear. Sounds are played into the ear and the response is measured. If the baby hears normally, there will be an echo that is picked up by the microphone. If there is no echo, the baby could have a hearing loss.
Auditory Brainstem Response (ABR) measures the brain’s ability to perceive sound. The baby is fitted with small electrodes placed on her head. The electrodes can pick up brain activity and will measure brain response when sounds are played into the baby’s ear.
Some hospitals may use both tests, and some may use the ABR as a backup when the baby fails the OAEs. Both tests are accurate, and are a good indicator that your baby has normal hearing. It is possible, however, for a baby with some hearing loss to pass these tests. Mild hearing loss only affecting a few frequencies may not be detected by the test. There are also genetic conditions that only affect hearing after the newborn period. So always keep vigilant for any sign that your baby is not hearing properly.
If your baby does not pass the initial test, there is still a good chance that she has normal hearing. About 2 to 10 percent of babies with no hearing loss do not pass the initial screening test. The reasons could be that there is fluid in the ear, or perhaps the baby was crying during the testing. In total, only about .2% of all babies, or about 2 per thousand, are born with hearing loss. If your baby does not pass the initial testing she will be referred for more intensive testing to determine if in fact she has hearing loss.
The first step in more thorough testing will be a diagnostic Auditory Brainstem Response. The first ABR that your baby had was a screening ABR. The diagnostic ABR will be more thorough. It will determine the softest sounds the baby can hear. If the baby is restless, he may be given a mild sedative to make sure his body movements or crying do not interfere with the test.
If the baby passes this test, his hearing is normal and there is no need for further testing. Always remain alert, however, for any changes in behavior that may signal a hearing loss.
CT / MRI Scans
To determine the cause of the hearing loss, the doctor may order a CT scan, an MRI scan, or both. A CT (computed tomography) scan will show the bony structures of the ear, and will determine if the cochlea is malformed. An MRI (magnetic resonance imaging) scan shows the soft tissue, and can determine if there is a tumor or other physical cause of the hearing loss.
The information obtained with these scans can determine how the hearing loss is going to be treated. If the infant needs a cochlear implant, the CT scan will show the structure of the cochlea to aid in the implant procedure.
If the CT or MRI scans do not show any physical cause for the deafness, genetic testing may be in order to determine the nature of the hearing loss. The first step would be to examine the infant to see if deafness is part of a syndrome or not. Syndromes are collections of symptoms seen together, and can affect many aspects of the child’s development. Deafness caused by syndromes represents about 30% of genetic deafness, while non-syndromic deafness accounts for about 70%.
There are over 400 sources of genetic congenital hearing impairment. By far the most common genetic cause of autosomal recessive deafness is a mutation of the Connexin 26 gene. Connexin genes are important in the development of hair cells in the cochlea. Deafness caused by Connexin 26 is characterized by profound loss of hearing from birth. Newborn infants with confirmed deafness can be tested for Connexin 26 (also known as GJB2). If both parents carry the mutated Connexin 26 gene, all of their children will have a 25% chance of being born deaf, and 50 % will be asymptomatic carriers of the gene (like the parents).
Many syndromic sources of congenital deafness have several other medical findings in addition to hearing impairment, such as problems with sight, balance, and liver/kidney/heart function. Identifying genetic causes of deafness is important because it will alert parents and doctors to possible future health problems for the child, and enable the parents assess their chances of having another hearing impaired child.
Once a child has been diagnosed with hearing loss, the options for treatment become much clearer. For children with cochlea defects, a cochlear implant may be prescribed. Others may benefit from hearing aids, or a combination of hearing devices and signing. Early diagnosis is extremely important. Language development begins from birth, and the hearing impaired child has special challenges to keep up to his maximum potential.
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