Hearing tests in newborns
In Germany and other countries, newborn babies are routinely given hearing tests in order to detect and treat hearing impairments as early as possible. This can improve early language development in children who have hearing problems.
Nearly all babies can hear well: 997 out of 1,000 babies are born with normal hearing. Up to 3 out of 1,000 newborns have a moderate or severe hearing impairment. Most of these children hear a little worse than normal, but aren’t deaf. Without early hearing tests, hearing problems are often first detected when a child is between 2 and 4 years old. But hearing tests in newborns can’t detect hearing impairments in all children because some hearing impairments only develop later on in childhood.
What happens if a newborn has a hearing problem?
If a baby can’t hear properly, the brain cells responsible for hearing aren’t used much. As a result, these cells may not develop properly, and the child’s hearing might be permanently affected. This is difficult to “fix” later on in life. Children who don’t hear well might learn to talk later than other children. This, in turn, can affect their ability to learn in general, as well as their personal and social development.
How are hearing impairments diagnosed?
It is difficult to judge whether babies can hear well. Whereas older children can actively participate in tests that check their reaction to tones and sounds, that’s not possible with babies. In the “objective” test methods that are used in newborn hearing screening, the child doesn’t even need to be awake. Two approaches are particularly suitable for testing hearing in newborns:
- otoacoustic emission measurements and
- the auditory brainstem response (ABR) test.
These tests don’t hurt at all and can be done while the baby is sleeping. Newborn hearing screening is routinely offered in all hospitals in Germany.
What are “otoacoustic emissions” and how are they measured?
Otoacoustic emissions (OAE) are measured using an approach based on echoes. A small probe is placed inside the outer ear, where it repeatedly makes a soft “clicking” sound. These sounds travel to the inner ear, right through to the fine hair cells of the cochlea. These cells usually “respond” by vibrating – the vibrations are then carried from the inner ear back to the outer ear in the form of sound waves. There, a tiny microphone on the probe picks up the sound waves and measures how strong they are. If there is no response, or if it is very weak, the cochlea may not be receiving sounds properly. This problem is often caused by hair cells not working as they should.
But abnormal test results don’t always mean that the baby is hard of hearing. For instance, the sound waves might not be measured properly if the child doesn’t keep still, has fluid in his or her ear, or if background noises interfere. And the OAE test doesn’t measure how severe the hearing loss is. Although the test is relatively accurate, it sometimes fails to detect hearing impairments. This is known as a “false negative” test result.
Sometimes newborns with normal hearing get a wrong diagnosis after having an OAE test: Although they can hear well, they are mistakenly diagnosed as being hard of hearing. This is called a “false positive” test result. Wrong diagnoses like this are usually quickly corrected when further tests are done.
The OAE test is simple and normally only takes a few minutes. It is done in a quiet environment and, if possible, when the baby is completely relaxed or asleep. This is because the results could be affected if, for instance, the baby makes a sound like sucking noises during the test.
How does auditory brainstem response (ABR) test work?
This test measures whether sound waves are passed on to the brain properly. It is a special kind of electroencephalogram (EEG) – a test that measures electrical activity in the brain. It is also called “brainstem-evoked response audiometry (BERA).” Before the test is done, small sensors (electrodes) are stuck on the baby’s scalp and behind his or her ears. The baby is then given special headphones, through which clicking noises are sent to the inner ear. The electrodes measure whether the brain receives the sound waves from the inner ear, in the form of electrical signals. If the signals don’t reach the brain properly, then the baby might have impaired hearing.
Like the other test, this test also needs to be done in a quiet environment. The more active and more awake the baby is, the more electrical signals his or her brain produces. This makes it difficult to distinguish between signals from the hearing nerves and other signals. So the test works best if the baby is asleep during it.
Together with the OAE test, the auditory brainstem response test can help determine whether the hearing loss is caused by damage to the inner ear or damage to the hearing nerve.
What are the advantages of doing these tests immediately after birth?
Hospitals offer the best possibilities for testing a large number of babies soon after they are born.
Treatment for hearing impairments would not be started at such a young age. But detecting a hearing problem very early on in a child’s life can help others better understand his or her behavior, and avoid interpreting it wrongly – for example, if the child hardly reacts when spoken to. Hearing impairments can also develop later on in childhood, though, due to things like infections in toddlers. So even if hearing tests show that there’s nothing wrong with a child’s hearing, it’s still important to keep monitoring whether he or she can hear well.
If a hearing impairment is discovered, treatment can be started as soon as possible. There is some evidence that speech and language develop better in children whose hearing impairment was detected during newborn screening tests compared to children whose hearing impairment was diagnosed later. Not enough is known about how an early diagnosis affects the long-term psychological wellbeing and quality of life of these children. The treatment options include hearing aids, speech therapy, and patient education. Cochlear implants (electronic hearing aids) might be surgically implanted in certain cases.
Crockett R, Wright AJ, Uus K, Bamford J, Marteau TM. Maternal anxiety following newborn hearing screening: the moderating role of knowledge. J Med Screen 2006; 13(1): 20-25.
Deutsche Gesellschaft für Phoniatrie und Pädaudiologie (DGPP). S2k-Leitlinie: Periphere Hörstörungen im Kindesalter. AWMF-Registernr.: 049-010. September 2013.
Institute for Quality and Efficiency in Healthcare (IQWiG, Germany). Neonatal screening for early detection of hearing impairment: Final report; Commission S05-01. February 28, 2007. (IQWiG reports; Volume 19).
Morzaria S, Westerberg BD, Kozak FK. Systematic review of the etiology of bilateral sensorineural hearing loss in children. Int J Pediatr Otorhinolaryngol 2004; 68(9): 1193-1198.
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