photo credit http://www.embell.co.uk
Thanks to technology, we can actually diagnose hearing loss within hours of a baby’s birth! Most states require all babies to have a hearing screening before leaving the hospital. This is an important first step in identifying babies with hearing loss. The sooner babies are diagnosed with hearing loss, the sooner intervention can begin, and the more normal the baby’s speech and language development will be.
Did you know? According to the American Speech-Language and Hearing Association, 3 out of every 1000 babies delivered will be diagnosed with hearing loss.
How is this testing done?
There are two ways in which newborn hearing screening is done. The first test is called an otoacoustic emissions (OAE) test. A small earphone is placed in each of the baby’s ears. The earphone contains a tiny microphone and speaker. First, a series of tones or clicks come into each ear from the speaker. If tiny sensory cells in the inner ear, called outer hair cells, are working correctly, a small sound is actually emitted from the ear and is recorded by the microphone. The loudness of these sounds is then compared to normative data in a computer program that show us if these sounds are within the range of normal.
Here is an example of what a passing distortion product otoacoustic emissions test for the left ear looks like. The OAEs are in blue, the noise levels are in green.
Photo credit http://www.bradingrao.com
For more information on otoacoustic emissions, testing, click here.
The second test is called an automated auditory brainstem response (AABR) test. Small sticky electrodes are placed behind the baby’s ears and on the forehead. Small earphones with a tiny speaker are inserted into the baby’s ears. Soft tones or clicks come into each ear from the speaker, and the electrodes pick up the auditory nerve’s response to these sounds, which are recorded as waveforms. These waveforms are compared to normative data in the computer to see how soon they occur after the stimulus and how large they are.
Here is an example of an ABR tracing. The major waveforms are numbered. The top graph has waveforms that are more robust and also occur close together in time, which suggests that the patient was being tested with a higher intensity sound. As you look at the other waveforms, you can see that they gradually diminish in height and are occur farther apart in time. This occurs when softer level stimuli are used. When the intensity of the sound gets below a person’s threshold of hearing, the waveforms are either absent or very delayed.
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For more information on automated auditory brainstem response testing, click here.
Both of these tests can take only minutes with a quiet, sleeping baby! The result of both tests will either be a PASS or REFER for each ear. If your infant has a REFER result, prompt follow-up should be scheduled for a more thorough evaluation.
Keep in mind that OAE and AABR are not truly hearing tests. They both test different parts of the auditory system and to some extent they can give us clues about the child’s hearing loss. However, behavioral hearing testing is necessary to know for sure the type and degree of hearing loss a child has. See more about this under the “Hearing testing for children” tab.