Any mother will know that growing a baby is no easy task. And unfortunately, there are a number of things that can go wrong in the process. One of these things is a failure to develop normal hearing, a condition known as congenital hearing loss. Congenital hearing loss is one of the most common long-term conditions in children. In the US, the prevalence of hearing loss in newborns sits around 1.7 per 1000 babies.
Hearing Loss and Deafness
For normal hearing, the ear and all its little bits and pieces need to work together to convert sound into nerve impulses. These neural signals must then be able to make their way down the auditory pathway to the brain for processing.
Hearing loss can be conductive, sensorineural, or mixed. Conductive hearing loss involves abnormalities of the outer or middle ear. For example, a hole in the eardrum, your ear canal being plugged with earwax, or fluid build-up in the middle ear from a cold. Conversely, sensorineural hearing loss occurs when there’s a problem with the inner ear, auditory nerve, or central auditory pathway in the brain. Examples of sensorineural hearing loss include those due to damage from certain medications, head trauma, or viral infections. Mixed hearing loss is a combination of conductive and sensorineural factors.
What Causes Congenital Hearing Loss?
No parent wants to hear that their little bundle of joy is any less than perfect. However, the reality is that congenital hearing loss is not as uncommon as we’d like it to be. In most cases, this hearing impairment is due to genetic factors. Over 180 genes have been studied for their link with congenital hearing loss. A defect in these genes can result in abnormal development of various parts of the ear, including the cilia hair cells of the ear or even the nerves that carry sound to the brain. Having a family history of congenital hearing loss as a risk factor has been suggested, though research has found that less than 2% of children with a relevant family history have hearing loss themselves.
Other risk factors for congenital hearing loss include:
- Parasitic or viral infection while in the womb – the frequent culprits here are toxoplasmosis, cytomegalovirus (CMV), rubella, and the Zika virus
- Low birth weight
- Injuries or trauma to the baby during the birthing process
- Maternal drug or alcohol use while pregnant
If the mother has gestational diabetes while pregnant or problems with blood pressure (preeclampsia), this can also contribute to a risk of congenital hearing loss.
In addition to these risk factors, congenital hearing loss can also be associated with a syndrome, such as Down syndrome or Usher syndrome.
Can Congenital Hearing Loss be Treated?
Screening for Congenital Hearing Loss
There is currently no cure for congenital hearing loss (or indeed, most forms of hearing loss acquired later in life either). However, congenital hearing loss can be prevented in many instances by:
- Immunization of the mother from diseases with available vaccines, such as rubella
- The mother abstaining from drugs and alcohol while pregnant
Though hearing loss in newborns can’t be cured, it can be managed. Because evidence unequivocally points to early treatment and intervention being beneficial for child development, many countries have introduced universal newborn hearing screening, including the USA. While previously, only high-risk babies were screened for hearing impairment, nowadays, all babies (with their parents’ consent), will undergo a hearing screening test, sometimes before they’ve even left the hospital.
Because babies have a hard time sitting in an acoustic booth and pressing a button every time they hear a tone through a pair of headphones as during a normal audiometry test, clever scientists have developed a way to objectively measure the brain’s responses to sound. Essentially, baby wears a device over his or her head and ears. This device presents sounds through the earphones, which stimulate a response from the ears and auditory pathways. If measuring something called oto-acoustic emissions, a probe can detect the motion of the eardrum (tympanic membrane) in response to these sound waves. If the test is measuring auditory brain stem responses, electrodes on the scalp can detect brain activity in response to the test sounds. In this way, even though baby can’t tell you what they’re hearing, you can get a good idea that the ear and/or the brain is able to detect the sound.
If baby doesn’t pass the screening test, they will be referred on for more comprehensive assessment of their hearing and general health; ideally this happens before they turn three months old. However, it is important to note that the neonatal screening methods don’t detect forms of congenital hearing loss that manifest a bit later. So, if you know your baby has risk factors for hearing loss or you are concerned at all even a few months down the track, it’s important to see a hearing healthcare professional even if there were no problems flagged during the newborn screening test.
Management of Congenital Hearing Loss
For babies with congenital hearing loss, it is possible to provide them with the best chance at experiencing normal hearing through certain devices.
Conventional hearing aids are often the device of choice for those with mild to severe sensorineural hearing loss and in certain cases of conductive hearing loss. However, once the sensorineural hearing loss passes into the severe to profound levels, a cochlear implant tends to provide superior performance for understanding speech and clarity of sound. Many eligible children with congenital hearing loss are fitted with a cochlear implant even before they turn a year old. Another intervention for aiding hearing is bone-anchored hearing aids. These can be useful for children with conductive hearing loss due to abnormal development of the parts of the ear canal and where surgical reconstruction is not possible.
Since hearing impairment in children is associated with delayed development in reading, thinking skills, and emotional skills, it’s important to keep on top of signs of hearing loss and not to delay in seeking help. Research tells us that treatment before the age of six months, such as with hearing aids, provides a significantly better chance of minimizing the developmental delays that can be caused by hearing loss.
Congenital hearing loss. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5675031/
Hearing Loss at Birth (Congenital Hearing Loss). https://www.asha.org/public/hearing/congenital-hearing-loss/
Congenital Hearing Loss: Overview and More. https://www.verywellhealth.com/congential-hearing-loss-5210221