The purpose of the Newborn Hearing Screening (NHS) program is to identify hearing loss in infants early, which is crucial for optimal speech and language development. While the screening is highly effective, it provides only a snapshot of the baby’s hearing health at the time of the test. A pass result does not guarantee perfect hearing, and in rare cases, specific types of hearing impairment can be missed by the initial screen, making continued monitoring essential.
Understanding the Newborn Hearing Screen
The newborn hearing screen relies on objective, physiological tests that do not require the baby’s behavioral response. Two primary methods are often used in combination to assess different parts of the auditory system. The first is Otoacoustic Emissions (OAE), which measures a tiny sound echo produced by the cochlea’s outer hair cells when stimulated by sound, confirming if the inner ear is working correctly.
The second method is the Automated Auditory Brainstem Response (AABR) test, which measures the brain’s electrical activity in response to sound. Small electrodes placed on the baby’s head record how the hearing nerve and auditory brainstem respond. The AABR test assesses the entire hearing pathway, from the inner ear up to the brainstem, providing a broader picture of auditory function.
These screening tools are designed to catch significant hearing loss, typically moderate to profound. Passing either test primarily confirms the mechanical function of the peripheral auditory system at birth. However, because they are screening tools and not full diagnostic evaluations, they have technical limitations that can result in a false-negative result, where a baby with a hearing issue is incorrectly identified as having normal hearing.
Hearing Loss Conditions Missed by Initial Testing
A primary reason a baby might pass the screen but still have hearing difficulties is Auditory Neuropathy Spectrum Disorder (ANSD). This condition occurs when the cochlea’s hair cells function normally, leading to a “pass” on the OAE test. However, the signal traveling along the auditory nerve to the brain is disorganized or blocked, requiring the AABR test to identify the neural transmission issue.
Another challenge is the detection of mild or high-frequency hearing loss. Screening protocols are calibrated to flag moderate-to-severe losses, so a milder loss may not trigger a “refer” result. Hearing loss restricted to the highest frequencies, which are not always covered by the screening stimulus, can also be missed. These subtle losses can still impact a child’s ability to hear specific speech sounds, such as “s” or “f,” affecting language development.
Progressive or delayed-onset hearing loss affects children who pass the screen but develop impairment later. This type of loss, which can be genetic or related to infections or medical conditions, develops months or years after the initial newborn screen. Up to 8.4% of children later diagnosed with hearing loss had initially passed their newborn hearing screening. This underscores that the screen is a single point of assessment, not a guarantee against future hearing issues.
Developmental Milestones for Ongoing Monitoring
Parental observation of a child’s response to sound remains the next layer of detection after the newborn screen. Monitoring behavioral milestones is a simple, ongoing way to track auditory development throughout the first year. From birth to three months, infants should react to loud sounds with a startle reflex and calm down when they hear a familiar voice. They will also begin making sounds other than crying, such as cooing.
Between four and six months, a baby should turn their head or eyes toward a new sound and begin to imitate their own sounds, like “ooh” or “aah”. They start to recognize and respond to changes in the tone of a parent’s voice. Failure to look for the source of a sound can be an early indicator that the hearing pathway is not fully functioning.
The period from seven months to one year brings more complex milestones, including responding to their name when called and understanding simple words like “no” and “bye-bye”. Infants should be actively babbling with repeated syllables, such as “mama” or “baba,” and trying to imitate simple words. If a child is not meeting these key speech and hearing milestones, parents should consult their pediatrician or an audiologist for a full diagnostic hearing evaluation, regardless of the initial screening result.