Development of hearing
Our sense of hearing starts developing as early as the second month of pregnancy. By 18 weeks of pregnancy, babies are thought to hear their very first sounds. Babies in the womb at around week 25 or 26 have been shown to respond to voices and noise. In their fluid filled environment though the sounds are likely to be muffled and therefore responses to sound are difficult to measure.
Once the baby is born, it is difficult to tell sometimes if they are hearing however hearing tests are done to determine any difficulties. In the first couple of months babies’ responses are very subtle and difficult to observe. They may startle to loud sounds, wake to some sounds, stir in their sleep or show other body responses such as eye widening or body tensing. The sounds they respond to are usually sudden loud or sharp sounds such as a door banging, someone sneezing or a toddler squealing. Babies of this age are unable to turn to their names and rarely respond to softer sounds.
By 4-6 months of age babies begin to develop the ability to turn towards the direction of sound but only if it is on the same level of the ear. They can be soothed from crying by the sound of a voice and their eyes can often shift towards the source of a sound. Over 6-month-old babies can turn well to the direction of sound and will listen when you speak to them. They will begin to understand some simple words and will begin to babble. More complex sounds such as musical toys and TV jingles will be more interesting to them.
By 10-12 months old your child should be responding to sounds from any direction. They should be able to turn to their name and recognise familiar sounds around them. They should be babbling and starting to form words such as mum, dad and no.
What signs should I look for if I suspect my child has a hearing loss?
If you suspect your child has a hearing loss the best thing you can do is contact an Audiologist to perform a hearing test. It is advised that you do not try assessing the child’s hearing yourself as this may lead to unnecessary anxiety. You can observe your child’s responsiveness to sound which may be useful information for the Audiologist.
- Are they responding to a variety of sounds at home? Observe your child at different times during the day. Look for signs that they can hear a favourite TV jingle from another room or the crackle of you opening a biscuit packet from a distance. Ensure the child is not too distracted or tired or that the house is not too noisy.
- Is their speech developing appropriately? This is often the first obvious sign of late onset hearing loss or temporary hearing loss. Discuss with your maternal and child health nurse, GP or speech pathologist to determine if there is a speech delay.
- Do they have recurrent ear infections, throat infections or colds? This is the most common reason for hearing loss in children under the age of 7. Fluid or mucous builds up in the normally air-filled space in the middle ear and results in a temporary hearing loss similar to listening under water. This is often temporary and can be fixed surgically if it is a persistent issue. Your child would need to see an Ear, Nose and Throat doctor for management.
- Is there a history of hearing loss in the family from a young age? There are certain hearing losses that are hereditary. These hearing losses often are diagnosed in childhood and can progress to worsening hearing as an adult. Genetic tests are currently available for some of the genes which are known to cause hearing loss.
- Did my baby have a newborn hearing test? In all states in Australia, newborn hearing screening tests are offered to babies before discharge from hospital. If your baby was born at home or overseas, they may have missed the screen. You can contact your closest Audiology department or ask your GP for details of where you can arrange a hearing test.
- Could there be other reasons my child is not responding to sound? Sometimes children with developmental delays or physical delays may not show clear responses to sound. Children with Autism Spectrum Disorder often show little interest in environmental sounds. Extremely premature babies may be delayed with their responsiveness and babies or children with physical disabilities may not be able to turn their heads in response to sound.
Types of hearing loss in children
Conductive hearing loss
This is the most common hearing loss in children and is a result of a build-up of fluid or mucous in the middle ear space. This occurs when there is a blockage in the eustachian tube which connects the nose and the ear. This eustachian tube usually acts to equalise the air pressure in the middle ear cavity. The eustachian tube can become blocked with a cold or as a result of enlarged tonsils and/or adenoids which sit at the base of the nose. If the eustachian tube stays blocked for long enough the mucous can build up in the middle ear cavity and can remain there until the eustachian tube is able to clear the blockage.
In many cases the child presents with hearing loss as a result of this fluid in the ear. It can be in one or both ears and can fluctuate depending on how blocked the ears are. The degree of hearing loss can range from a very mild dulling of sound to a more serious deficit resulting in speech sounds being reduced to a whisper. The hearing loss is generally temporary with the hearing nerve remaining intact. The fluid can resolve on its own or may need medical treatment, some even require minor surgery with grommets to aerate the middle ears. If the conductive hearing loss is due to structural abnormality of the middle ear, in some cases it may not be surgically corrected. Special hearing aids are suitable for these children to access hearing to develop speech and language.
Conductive hearing loss is most common in younger children but can happen at any age. Tell-tale signs of conductive hearing loss could include:
- Pulling/tugging/banging ears
- Recurrent ear infections
- Sensitivity to sudden loud sounds (eg vacuum, hand dryer)
- Constant colds/snotty nose/snoring
- Slower than expected speech development
- Balance issues
- Learning delays in school aged children
Sensorineural hearing loss
Less common than conductive hearing loss but current statistics suggest 1 in 1000 children in Australia have a sensorineural hearing loss. These hearing losses are defined as losses due to an impairment in the nerve of hearing or cochlea. Hearing loss can be in one ear or both ears and can vary in degree from very mild to no hearing at all. The cause of sensorineural hearing loss is not always known. The most common causes are genetics, ototoxic medications administered as newborns, illnesses such as meningitis, maternal CMV, jaundice, chromosomal abnormalities and extreme prematurity. Children can be born with the sensorineural hearing loss or it can be acquired later in childhood.
Mixed hearing loss
A mixed hearing loss is where a child has a combination of a conductive hearing loss and a sensorineural hearing loss. Often the conductive hearing loss is temporary and can resolve or be medically treated. In some cases, particularly if the child has a syndrome involving structural abnormalities such the child has hearing loss at the nerve but also some conductive loss due to a malformation of the middle ear.
Auditory Neuropathy Spectrum Disorder
ANSD is a very rare condition where the cochlea shows response to sound but the signal to the brain becomes disrupted and this results in a hearing impairment. This nerve disruption or dyssynchrony is more common in very premature babies, those with high jaundice at birth and in some genetic conditions.
How can I check if my child has a hearing loss?
Audiologists are university trained specialists in hearing assessment. You are best to see a Paediatric Audiologist especially if your child is under 7 years of age. Different age groups require different modes of assessment and sometimes several techniques are used to obtain an accurate result. All Audiologists should perform middle ear function tests and some form of hearing assessment to gain a good understanding of your child’s hearing and middle ear status. They may refer your child for further medical advice depending on the result.
What happens if my child has a hearing loss?
If a child has been diagnosed with a hearing loss it will depend on the degree and type of hearing loss as to how the hearing loss is managed. If the hearing loss is medically treatable the Audiologist will refer you to an Ear, Nose and Throat specialist to determine if grommet surgery or similar is warranted. If the hearing loss is more permanent, then the impact on the child’s development will be determined. If it is thought that the hearing loss is likely to delay a child’s speech development or learning, then hearing aid fitting may be recommended. In cases where children have severe or profound hearing losses or ANSD, cochlear implantation may be an option.
In all cases the development of speech and language is of the utmost importance to the Audiologist. Their job is to accurately diagnose and manage hearing losses in children. Speak to your GP, maternal and child health nurse or paediatrician if you are unsure of Audiological services in your area. Attune Hearing is Australia’s only accredited hearing healthcare provider, offering hearing services to those who need help on their hearing journey.