Overview
Definition:
Newborn hearing screening (NHS) is a critical public health initiative designed to identify infants with hearing loss at birth or shortly thereafter
Early identification allows for timely intervention, which is crucial for optimal speech, language, and cognitive development
The two primary objective methods used are Otoacoustic Emissions (OAEs) and Auditory Brainstem Response (ABR).
Epidemiology:
Permanent congenital hearing loss affects approximately 1-3 per 1000 live births
The prevalence is higher in neonatal intensive care unit (NICU) graduates, reaching up to 1 in 100
Universal newborn hearing screening (UNHS) programs aim to screen all newborns before hospital discharge.
Clinical Significance:
Undiagnosed hearing loss can lead to significant developmental delays, including speech and language impairments, academic difficulties, and social-emotional challenges
Early detection and intervention can mitigate these negative outcomes, significantly improving a child's quality of life and long-term prognosis
This screening is a cornerstone of preventative pediatrics and neonatal care.
Diagnostic Approach
History Taking:
Focus on family history of childhood hearing loss
Inquire about prenatal and perinatal factors such as maternal infections (cytomegalovirus, rubella), prematurity, low birth weight, hyperbilirubinemia requiring transfusion, ototoxic medications used during pregnancy, and NICU stay exceeding 5 days
Assess for congenital anomalies of the head and neck, syndromes associated with hearing loss (e.g., Down syndrome, Usher syndrome), and meningitis
Red flags include a known history of hearing loss in the family or significant risk factors
Note any infant behaviors suggesting poor auditory response.
Physical Examination:
A thorough head and neck examination is essential
Look for dysmorphic features suggestive of genetic syndromes associated with hearing loss, such as low-set ears, ear tag anomalies, or cleft palate
Examine the ear canals for atresia or significant cerumen impaction
Evaluate for any signs of congenital infections or neurological abnormalities
While a direct physical exam cannot confirm hearing loss, it can identify risk factors and associated anomalies.
Investigations:
The primary investigations are objective hearing screening tests
Otoacoustic Emissions (OAEs) measure the response of the cochlea to sound, specifically the "echo" produced by the outer hair cells
Transient Evoked OAEs (TEOAEs) and Distortion Product OAEs (DPOAEs) are commonly used
Auditory Brainstem Response (ABR) measures the electrophysiological activity in the auditory nerve and brainstem in response to auditory stimuli
Automated ABR (AABR) is often used for screening, while diagnostic ABR requires sedation and more precise interpretation
If initial screening fails, diagnostic audiologic evaluations including behavioral audiometry (e.g., visual reinforcement audiometry, play audiometry) and formal ABR are performed
Genetic testing may be considered in select cases.
Differential Diagnosis:
The primary differential in this context is not a disease but rather the cause of a failed screen
A failed screen can be due to true hearing loss or temporary factors like vernix or amniotic fluid in the ear canal, or a noisy testing environment
Therefore, the differential for the failed screen includes: conductive hearing loss (e.g., otitis media with effusion, cerumen impaction, atresia), sensorineural hearing loss (congenital or acquired), and even neuromotor/developmental delays affecting the child's ability to respond
Persistent failed screens warrant referral to an audiologist for a comprehensive diagnostic evaluation to determine the type, degree, and configuration of hearing loss.
Management
Initial Management:
If a newborn fails the initial hearing screen (typically performed with OAEs or automated ABR), the infant should be rescreened before hospital discharge or within the first month of life
If the infant continues to fail the rescreen, a diagnostic audiological evaluation by a qualified audiologist must be scheduled by 3 months of age.
Medical Management:
Medical management is not directly applicable to the screening process itself
However, if hearing loss is diagnosed, management focuses on the underlying cause if identifiable and treatable (e.g., treatment for meningitis or congenital infections)
For most sensorineural hearing losses, medical management is not an option
rather, intervention focuses on audiological and educational rehabilitation.
Surgical Management:
Surgical intervention is rarely indicated for congenital hearing loss identified during newborn screening, except in cases of specific anatomical abnormalities of the ear (e.g., microtia with atresia) which may be addressed later
Cochlear implants or bone-anchored hearing aids are prosthetic devices, not surgical cures for the hearing loss itself, and are considered for severe to profound hearing losses not adequately managed by conventional hearing aids.
Supportive Care:
Supportive care is crucial for families of infants diagnosed with hearing loss
This includes genetic counseling, early intervention services (e.g., speech therapy, auditory training, sign language instruction), and ongoing psychosocial support
Education for parents regarding communication strategies, amplification devices, and educational options is paramount
Regular follow-up with audiology, speech therapy, and pediatric developmental specialists is essential.
Complications
Early Complications:
The primary "complication" of delayed diagnosis is the irreversible impact on speech and language development
Other early issues can include parental anxiety and distress due to the screening process and potential diagnosis
Missed diagnosis can lead to significant delays in initiating habilitation services.
Late Complications:
Long-term complications of untreated hearing loss include significant deficits in spoken language, reading, and academic achievement
Social isolation, behavioral problems, and reduced employment opportunities can also occur
The extent of these complications is directly related to the degree of hearing loss and the age at which effective intervention begins.
Prevention Strategies:
The most effective prevention strategy is universal newborn hearing screening followed by timely diagnostic evaluation and intervention for any identified hearing loss
Adherence to screening protocols, prompt referral for diagnostic testing, and ensuring families access early intervention services are critical
Public health campaigns to raise awareness about hearing loss risk factors and the importance of screening are also vital.
Prognosis
Factors Affecting Prognosis:
The prognosis for children with hearing loss identified through newborn screening is significantly better than for those diagnosed later
Key factors influencing prognosis include: the degree and type of hearing loss, age at diagnosis, age at initiation of intervention (audiological and educational), the availability and quality of early intervention services, parental involvement and support, and the presence of co-occurring conditions.
Outcomes:
With early identification (by 6 months of age) and appropriate intervention, children with hearing loss can achieve age-appropriate language, communication, and cognitive development
Outcomes vary based on the severity of hearing loss and individual child factors, but early habilitation greatly improves the likelihood of successful integration into mainstream education and society.
Follow Up:
Infants who pass newborn hearing screening should have their hearing monitored periodically, especially if risk factors for late-onset or progressive hearing loss are present (e.g., family history, certain syndromes, exposure to ototoxic medications, recurrent ear infections)
Children diagnosed with hearing loss require ongoing, regular follow-up with audiologists, speech-language pathologists, and other specialists as needed, often continuing throughout childhood and adolescence.
Key Points
Exam Focus:
Understand the principles behind OAEs and ABR, their advantages, disadvantages, and indications for use in newborn screening
Know the typical screening protocol: initial screen, rescreen, and diagnostic follow-up timelines (screen by 1 month, diagnose by 3 months, intervene by 6 months – the 1-3-6 rule)
Recognize risk factors for hearing loss that may require more frequent monitoring or earlier diagnostic evaluation
Be familiar with the 10-20% false-positive rate of OAEs due to transient factors.
Clinical Pearls:
Always consider transient causes for a failed screen (e.g., vernix, amniotic fluid)
A clean ear canal and a quiet environment are crucial for reliable OAE testing
ABR is more sensitive for detecting neural pathway issues and is less affected by middle ear effusions than OAEs
Early intervention is key
emphasize the 1-3-6 guideline to parents and clinical teams
Advocate for universal screening and prompt follow-up.
Common Mistakes:
Failing to schedule timely diagnostic evaluations after a failed screen
Assuming a failed screen is definitively hearing loss without further audiologic assessment
Over-reliance on one screening modality without understanding its limitations
Inadequate follow-up for infants with risk factors for late-onset hearing loss
Delays in initiating intervention once hearing loss is confirmed.