Universal newborn hearing screening programs have significantly advanced the early identification of hearing loss, which greatly improves long-term communication outcomes. While a “pass” result provides immense relief, a small number of children who pass the initial screening are later found to have a hearing impairment. Understanding the screening’s limitations and the reasons for a false pass offers a clearer picture of why continued monitoring is necessary.
Understanding Newborn Hearing Screening
Newborn hearing screening is a quick, non-invasive procedure typically conducted within the first few days after birth for early detection. This is a screening tool, distinct from a full diagnostic evaluation performed by an audiologist. Its goal is simply to flag babies who might have hearing loss, resulting in a “pass” or “refer” result.
The two main methods used are Otoacoustic Emissions (OAEs) and Automated Auditory Brainstem Response (AABR). OAEs measure sounds produced by the outer hair cells in the cochlea when stimulated, testing the inner ear function. The AABR test uses electrodes to record the electrical activity of the auditory nerve and brainstem in response to sound, testing the entire hearing pathway. Both tests are objective and performed while the baby is asleep, requiring no behavioral response.
Reasons for Passing Despite Hearing Impairment
A baby can pass the newborn screening but still have a hearing impairment due to the limitations of the testing technology. A significant reason for a false pass is Auditory Neuropathy Spectrum Disorder (ANSD). In ANSD, the cochlea’s outer hair cells function normally, often resulting in a “pass” on the OAE test. However, the issue lies in the auditory nerve or the synchronization of signals traveling to the brain, leading to disorganized sound processing despite a functioning inner ear.
Screening tests primarily check for moderate to severe hearing loss across a limited range of essential frequencies. This focus means the screening may miss a mild or high-frequency hearing loss that could still impact a child’s speech and language development. While temporary issues like fluid in the ear canal often cause a false “refer” result, subtle underlying issues may not be detected by the screening. Approximately 8.4% of children later diagnosed with hearing loss had passed their initial newborn screening.
Monitoring for Progressive or Late-Onset Hearing Loss
A successful newborn screening confirms hearing pathways were working adequately at the time of the test, but hearing loss can still develop later in childhood. This is known as progressive or late-onset hearing loss, and its causes differ from the limitations of the initial screening. Genetic factors are a common cause, where an inherited gene causes hearing loss to develop gradually over the first few years of life.
Acquired Causes
Acquired causes related to illness or injury are a major concern for late-onset hearing impairment. Congenital Cytomegalovirus (CMV) infection is a leading cause, often resulting in progressive hearing loss during a child’s early years. Other serious childhood infections, such as bacterial or viral meningitis or mumps, can also lead to acquired hearing loss after a baby has passed the screening. Ototoxic medications, such as some chemotherapy agents, can also damage the inner ear, necessitating continuous monitoring.
Key Developmental Milestones to Watch
Parents serve as the primary monitors for functional hearing development following the initial screening. Observing a child’s responses to sound and developing communication skills provides the earliest signs that further evaluation is needed. If a child consistently misses age-appropriate milestones, parents should consult their pediatrician for a referral to an audiologist for comprehensive diagnostic testing, regardless of the initial “pass” result.
Milestones by Age
- In the first three months, a baby should startle or blink at loud, sudden noises and react to a familiar voice.
- Parents should also listen for cooing sounds that are distinct from crying during this period.
- Between four and six months, a baby should consistently turn their head to look for the source of a sound.
- They should also begin to engage in vocal play, making sounds like “ooh” and “aah.”
- By seven to twelve months, the baby should respond to their own name and understand simple words like “no” or “bye-bye.”
- They should also begin babbling repetitive consonant-vowel combinations like “mama” or “baba.”