Newborn hearing tests

Hearing tests in newborns and babies
Nearly all babies can hear well: 997 out of 1,000 babies are born with normal hearing. At the most, 3 out of every 1,000 newborns have a moderate or severe hearing impairment. Although these children hear a little worse than normal, most of them are not deaf. Hearing problems are often first detected when a child is between two and four years old. However, some hearing tests can already be carried out in newborns.

What happens if a newborn has a hearing problem?
If a baby cannot hear properly, it may be a result of conductive or sensorineural hearing loss. Conductive hearing loss is usually treatable and reversible. Sensorineural hearing loss is an injury to the cells within the hearing organ (cochlea) or the nerve of hearing;this usually is not reversible. The brain cells responsible for hearing are not used much. This means that the cells might not develop properly, and the baby’s ability to hear may be permanently affected. It is very difficult to make up for this later on. Children who do not hear well might possibly learn to speak 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 the hearing of newborns and babies is good. Whereas older children can actively participate in tests that check their reaction to tones and sounds, this is not possible with babies. In the “objective” test methods that are used in newborn hearing screening, the child does not need to actively participate, or even be awake. Two approaches are particularly suitable for testing the hearing of babies: “otoacoustic emission” measurement and “brainstem evoked response audiometry”.

These tests do not hurt at all and can be done while your baby is sleeping. Newborn hearing screening is not carried out on a routine basis in all hospitals.

What are “otoacoustic emissions” and how are they measured?
Otoacoustic emissions (OAE) are measured using an approach based on echoes. A small probe is put into the outer ear. The probe makes soft “clicking” sounds which travel to the inner ear, right through to the fine hair cells in the hearing organ called the cochlea. If the sound reaches them, the hair cells “answer” by vibrating. Like an echo, these vibrations are then carried from the inner ear back to the outer ear as sound waves. There, a tiny microphone on the probe picks up the sound waves and measures how strong they are. If there is no signal or if it is very weak, that could be a sign that the cochlea is not receiving sounds properly. This is often due to a problem with the hair cells.

But poor test results do not always mean that the baby is hard of hearing. Instead, the signal might not be picked up properly if the child does not keep still, has fluid in his or her ear or if there are background noises that interfere. And the OAE test does not measure how severe the hearing loss is. Although the test is relatively accurate, as with most tests, it may sometimes fail to detect a hearing impairment.

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. In other words, they get a “false positive” result. Wrong diagnoses like this can usually be quickly corrected if 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 sleeping. If, for instance, the baby makes sucking noises during the test, the results could be affected.

How does brainstem-evoked response audiometry (ABR or BERA) work?
This test measures whether sound waves are passed on to the brain properly. Brainstem-evoked response audiometry (BERA) is a special kind of electroencephalogram (EEG) – a test that measures electrical activity in the brain. It is also called the “auditory brainstem response” test (ABR).

Before the test is done, small metal plates (electrodes) are applied to the skin on top of the baby’s head 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 are not transmitted properly, then the baby might have a hearing problem.

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 your baby is asleep during it.

Both the OAE test and brainstem evoked response audiometry can indicate whether hearing has been affected by damage to the inner ear or to the hearing nerve. This test is painless and harmless. IT does not expose your baby to any radiation or harmful electric currents.

What are the advantages of these tests?
There are purely practical arguments for doing hearing tests immediately after birth. Hospitals offer the best possibilities for testing a large number of babies. However, treatment for hearing impairments would not be started at such a young age.

One advantage of early hearing tests is that they can provide information about whether a hearing problem can almost certainly be ruled out or not. This can help to understand the baby’s behaviour and avoid interpreting it wrongly, for example if he or she does not react when spoken to. Hearing impairments can also develop later on in childhood, though – for instance, due to infections in toddlers. So even if hearing tests show that there is nothing wrong with your child’s hearing, it is still important to keep looking out for any signs that he or she might have a hearing problem.

An early diagnosis also means it is possible to start treatment earlier. There is some evidence that children whose hearing impairment is detected during screening tests when they are newborns have better early language development compared to children whose hearing impairment is diagnosed later.

The treatment options include hearing aids, speech therapy, and special education. In the event that rofound hearing loss or deafness is diagnosed at an early age, it is possible to restore hearing with devices called cochlear implants. This involves surgically implanting an electronic device in the ear.