What Is the Newborn Hearing Screening Test?
Newborn Hearing Screens are Vital
Brand New Ears
The sense of hearing is well developed at birth. Babies can hear in the womb, and their brains begin organizing centers for listening and speech from a very early age. Babies and young children need access to sound to develop listening and speaking skills.
In the United States, the Newborn Hearing Screening program was implemented to screen every baby prior to discharge from the hospital. Children who are at risk for having a hearing loss are identified through this program. If a hearing problem is identified, the child is referred for more thorough testing.
Children who are born at home, or in a hospital which does not provide a newborn hearing screening test, should have their hearing tested as soon as possible. Most hospitals and doctor's offices are able to test babies' ears with a simple otoacoustic emissions test or an automated auditory brainstem response test.
Early Detection is Vital
While the incidence of a significant congenital hearing loss is only 3/1000, the benefits of early amplification and intervention are high. With the advent of digital hearing aids and cochlear implants, many profoundly deaf children are able to listen, speak, and sing if provided with early access to sound.
The ABR Screening Test
There are two main forms of testing performed for the Newborn Hearing Screening Program. The first type of test is called the Otoacoustic Emissions test, or OAE. The other screening test method is the Automated Auditory Brainstem Response test, or aABR.
Otoacoustic Emissions (OAE)
When the ear hears a sound, a healthy inner ear (cochlea) will send back an echo of that sound. The echo sound is called an otoacoustic emission, and there is a simple screening test which detects the production of OAE's. Children who do not produce OAE's are referred for further testing.
Automated Auditory Brainstem Response (aABR)
The auditory center of the brain is located in the brainstem, and simple EEG leads can detect brainwaves indicating a sound was detected by the brain. Typically, "clicks" are presented to each ear at a sound level of 35dB (the sound level of a very soft conversation). If the baby's brain indicates a response to that sound, then the test is scored as a "pass." If the baby does not show a reaction to the sound, the baby is referred for more testing.
Do You Hear What I Hear?
What Does a "Refer" Result Mean?
Both the ABR and OAE tests are affected by obstructions in the outer or middle ear, so if a baby has a lot of vernix, earwax, or fluid in the ear, a "refer" may be scored. Many babies who refer on the initial newborn hearing screening test will be re-tested after a couple of weeks to determine if the initial refer result was due to temporary fluid or vernix.
My Baby "Referred" on the Follow-Up Hearing Screening Test: Is My Baby Deaf?
The hearing screening tests do not diagnose a hearing problem. If an infant refers on a second screening test, the baby must be sent for more definitive, diagnostic testing. It is absolutely vital to obtain diagnostic testing if a baby refers on a second screening test, as the baby is now "at risk" for having a hearing problem.
The hearing screening test should not be performed more than twice, as it is possible to obtain a false "pass" on the test for children with mild hearing losses. If an infant refers on the newborn hearing screening test, then a follow-up with a pediatric audiologist and Ear, Nose, and Throat doctor (ENT) are necessary.
In addition, there are many levels of congenital hearing loss. The newborn hearing screening program is designed to detect moderate or greater hearing losses in babies. Some children with mild hearing losses may escape detection, and children with moderate hearing losses will appear to "hear" (startling at loud noises, for example) when a real hearing problem is present. It is impossible to tell if a baby can hear simply by observation, so getting a full diagnostic evaluation is vital.
When Baby Passes, But Doesn't Hear
Occasionally, an infant will pass the newborn hearing screening test a hearing problem will be found months (or years) later. While the newborn hearing screening test is an excellent screening device, it often misses slight to mild hearing losses. In addition, the program will not detect progressive hearing losses in children who had normal hearing at birth.
The "click" sounds produced in the newborn's ears are often a broadband high frequency sound. For this reason, babies who have a low frequency hearing loss (but normal hearing in the high frequencies) may be missed by the newborn hearing screening program. In addition, many children with mild hearing losses or low frequency hearing losses have present OAE's.
In hospitals that test via the OAE method, children with a condition called auditory neuropathy/dissynchrony are often not detected. Auditory dissynchrony is a hearing loss caused by a faulty relay of information along the auditory nerve. The inner ear is healthy, but the baby has difficulty hearing. Infants who have very high bilirubin counts (extreme jaundice), are in the Neonatal Intensive Care Unit (NICU) after birth, or are premature should have aABR testing performed alongside OAE testing.
A "two stage" screening approach has been recommended by many researchers. The two stage screening process would include both the OAE testing and the aABR testing to detect children with auditory dissynchrony and reverse-slope hearing losses. Currently, however, most hospitals employ only one screening method.
Some Hearing Loss is Hereditary
But We Don't Have Hearing Loss in Our Family!
Parents may be shocked when told their baby might have a hearing loss. While some families have a pattern of hearing loss among close relatives, over 90% of infants with congenital hearing loss are born to parents with normal hearing.
What Are the Causes of Congenital Hearing Loss?
Congenital hearing loss can be caused by genetics or may be acquired. Over 50% of hearing loss is caused by genetic factors, with the most common genetic cause being a change in the GJB2 gene (Connexin 26, a recessive trait).
Non-genetic hearing loss may be caused by congenital Cytomegalovirus (CMV), prematurity, lack of oxygen at birth, exposure to Gentamicin (an antibiotic), and more.
Approximately 25% of the time, the cause of a congenital hearing loss cannot be found, and the condition is termed, "idiopathic congenital hearing loss."
In some cases, a congenital conductive hearing loss will be identified. This type of hearing loss is potentially correctable, depending on the cause. A conductive hearing loss caused by fluid in the middle ear may be treated with tympanostomy tubes (ear tubes) to restore the child's hearing to normal levels. A conductive hearing loss caused by middle ear bone malformations may be treated with surgery.
What Are the Risk Factors?
Risk Factors: 0-28 Days Old
Family history of hereditary childhood sensorineural hearing loss
Birth weight less than 1500 grams (3.3lbs)
In utero infections (cytomegalovirus, rubella, syphilis, herpes, and toxoplasmosis)
Craniofacial anomalies (including the outer ear and ear canal)
Apgar scores of 0-4 at 1 minute or 0-6 at 5 minutes
Mechanical ventilation lasting 5 days or longer
Findings associated with a syndrome known to include a sensorineural and/or conductive hearing loss
Risk Factors: >28 Days Old
Neurofibromatosis Type II
Recurrent or persistent otitis media with effusion
Anatomic deformities and other disorders that affect eustachian tube function
In utero infection (e.g. Cytomegalovirus)
Family history of hereditary childhood hearing loss
Signs of Hearing Problems in Young Children
- Difficulty hearing some sounds, but not others
- Tilting the head when listening
- Speech delay or garbled speech
- Asks for instructions to be repeated
- Doesn't acknowledge the presence of others until they are within visual range
- Withdrawn behavior
- Frustration and frequent acting out
- Balance issues: may be slow to walk or stand
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