Newborn hearing screening

Hearing screening is a tool used to identify hearing impairment, or hearing loss, in newborn babies and young children. A test that shows hearing impairment or unclear results is usually followed up with a detailed diagnostic assessment carried out by an audiologist.

In Australia, every baby is offered screening for hearing loss. The sooner hearing loss is diagnosed, the better the outcomes. Hearing screening plays an important role in identifying and addressing hearing impairment because it can be difficult to tell if a baby has hearing loss during their first two months of life.

Hearing screening is non-invasive and is typically carried out by a nurse who has undergone specific training. Hearing screening can either be a single test, or a two-stage process. In two-stage screening, babies that show signs of hearing impairment in the initial test receive a second screening test. Only those showing a similar result in the second test are referred to an audiologist.

Hearing loss is classified by measuring the hearing threshold in decibels at various frequencies. Normal hearing has a threshold of 20 decibels (dB).

Hearing loss can be:

• Mild: 20-40dB;
• Moderate: 41-60dB;
• Severe: 61-90dB, and;
• Profound: more than 90dB.

Babies and young children identified as having moderate to profound hearing loss can receive support and early intervention to minimise the impact of their hearing impairment.

Screening tests

There are typically two tests that may be used to screen for hearing loss in newborns; an automated auditory brainstem response test, and otoacoustic emissions test. Screening typically takes place before the baby is discharged from hospital. The baby needs to be asleep or in a quiet and settled state during the screening test.

Automated auditory brainstem response test

This test measures the integrity of the inner ear and the auditory pathway. It can detect auditory neuropathy in children who are deaf, but who have normal otoacoustic emissions (as their cochlea is normal).

The stimulus is presented with either earphones or through an ear canal probe. Three specially-placed electrodes are used to detect the response from the brain stem. This is an automated device, so it can be performed by non-specialists. The test takes around 20 minutes to complete.

If the screening is not passed in one or both ears, the baby will undergo a second test, and may be referred to an audiologist for further assessment.

Otoacoustic emissions test

In a healthy cochlea, the hair cells vibrate in response to sound; this vibration generates acoustic energy, known as otoacoustic emissions.

This test measures the presence or absence of soundwaves being generated by the hair cells on the cochlea in response to sound stimuli. A miniature microphone is placed in the outer ear canal and the microphone produces sounds stimuli and then detects soundwaves generated by the cochlea.

If the screening test is not passed in one or both ears, the baby will undergo a second screening and may be referred to an audiologist for further assessment.

 

Hearing loss in newborns

Hearing is a critical part of a baby's cognitive, social and emotional development - a mild or partial hearing loss can affect their ability to speak and understand language. Young children with untreated hearing loss can experience delays in their language development, behavioural difficulties and underachieve at school.

It is estimated that around one in every 1000 babies is born with permanent hearing loss in both ears. The vast majority of deaf babies are born into families with normal hearing.

Causes

For around half of all babies and young children with hearing loss, there is no associated cause.

Some possible causes of hearing loss in newborn babies may include:

• Infections during pregnancy;
• Certain medications used during pregnancy;
• Nervous system disorders;
• Being born prematurely;
• Genetic syndromes such as Usher, Down syndrome or Waardenburg syndrome;
• A family history of hearing loss, and;
• Complications during birth.

Some other factors that can cause 'acquired hearing loss' any time after birth include:

• Certain medications;
• A perforated eardrum;
• Meningitis;
• Untreated middle ear infections, and;
• A serious head injury.

Risk factors

Most babies who are diagnosed with some degree of hearing loss do not have any known risk factors, nor any underlying medical condition that is associated with hearing loss.

Babies with an increased risk of hearing loss include those with:

• A family history of childhood hearing loss;
• High levels of jaundice;
• Abnormalities of the head and neck;
• Congenital infections (HIV, toxoplasmosis, syphilis, varicella, rubella, cytomegalovirus);
• Admission to newborn intensive care unit;
• Meningitis or encephalitis;
• Aminoglycoside antibiotic therapy for more than three days;
• Low birth weight (less than 1500 grams), and;
• The need for major cardiopulmonary resuscitation (CPR) at birth.

Babies at risk are typically offered repeat screening when they reach 9-12 months of age.

Types

Newborn hearing loss can be:

• Conductive - caused by damage to the outer or middle ear;
• Sensorineural - caused by damage to the inner ear structures, or;
• Mixed - a combination of both.

Sensorineural

Most newborn hearing loss is caused by sensorineural hearing loss. With up to half of cases due to genetic causes, the rest are acquired. It involves the cochlea or the auditory nerve.

Auditory neuropathy, one type of sensorineural hearing loss, is caused by absent or severely distorted auditory signals.

Conductive

Conductive hearing loss is usually caused by abnormalities of the outer or middle ear, which limit the amount of external sound that can pass through to the inner ear. The function of the cochlea remains normal, because the inner, middle and outer ear develop separately.

Signs and symptoms

Although hearing screening tests can identify the majority of babies with mild or more severe hearing loss, it is still important to monitor a young child's speech and language developmental milestones to detect late onset or progressive types of hearing loss.

During the first year, babies learn how to hear and recognise the sounds of their parents' language. They may experiment with sounds by babbling, which progresses to them making real words.

Some of the more typical milestones a baby reaches in their first year of life include:

• Startling or jumping with a sudden, loud noise;
• By three months of age, recognising a parent's voice;
• By six months of age, turning their head or eyes towards a sound, and;
• By 12 months of age, imitating some sounds and producing a few words such as 'mama' or 'bye'.

Babies and young children experience huge development in their speech sounds. By the age of two, around half of their speech can be understood, and by the age of three, most of their speech can be understood.

As the baby grows, some signs that may be associated with hearing impairment may include:

• Turning up the television volume excessively;
• Not replying when called;
• Having articulation problems with language and speech;
• Having difficulty understanding speech;
• Not being startled by sudden, loud noises;
• Poor academic performance;
• Being unable to determine where a sound is coming from, and;
• Speaking differently compared to other children their age.

Types of treatment

Early intervention services for newborn babies identified with a hearing impairment will enable improved speech, language and academic performance.

Potential complications

Hearing loss can:

• Impair the academic performance of children, and;
• Cause feelings of loneliness, isolation and frustration;

Adults with hearing loss can experience higher rates of unemployment.

Prognosis

Early intervention enables babies and young children to develop better language, speech and learning skills as their brain is exposed to language earlier. It is crucial for maximising the potential speech and language development of babies with hearing loss.

Prevention

Ways to help prevent hearing loss in babies and young children include:

• Vaccinations - to guard against preventable diseases that can cause a baby to be born with hearing loss;
• Getting proper treatment and follow-up for middle ear infections, and;
• Getting good prenatal care.