Early Detection and Intervention of Hearing Impairment

Deafness is the most common birth defect – every day, 33 babies are born with some form of hearing loss. The average age at which deafness is identified in the U.S. is 30 months, well after language and learning disabilities may have developed. Despite these numbers, approximately one-third of all infants go home from the hospital without having their hearing tested. So here, we’ll talk about how important early detection and intervention of hearing Impairment really is.

The incidence of Deafness in Newborns
Approximately 1 in 1,000 newborns is born profoundly – or fully – deaf.  Another 2 – 3 out of 1,000 babies are born with partial hearing loss, for a total incidence rate of approximately 1 in 300 babies born with some form of deafness. With an approximate birth rate of 4 million per year in the U.S., 12,000 infants are born with hearing loss every year.

The History of Infant Hearing Screening
In 1974, the Joint Committee on Infant Hearing recommended that only high-risk babies be screened for hearing loss. Consequently, high-risk screening programs were widely implemented and became the standard method of detecting infant hearing loss in the 1970s and 1980s.

These high-risk screening programs, many of which are still in place today, only screen approximately one in ten newborns for hearing loss. We know that Motivation effects Behavior so this has a deep impact. The ten percent screened are selected based on risk factors such as the family history of congenital hearing loss, low birth weight, malformations of the head and neck, and hyperbilirubinemia (an excess of organic detritus in the blood).

While selecting children based on risk factors is useful, it can not predict all babies which will be born deaf. Of the 12,000 babies born with hearing loss annually, only half exhibit a risk factor.

In 1991, Rhode Island performed the first large-scale clinical trial of universal newborn hearing screening (UNHS). Based on its results, in 1993 the National Institutes of Health Consensus Development Conference on Early Identification of Hearing Loss recommended that all newborns receive a hearing screening before being released from the hospital. The Joint Committee on Infant Hearing followed a year later with its own position statement supporting UNHS. Since 1993, the number of hospitals with UNHS programs has jumped from 11 to more than 1,000.

The Science Behind Screening

When discussing a medical screening procedure, there are two commonly used measurements:

  • Specificity refers to the proportion of people without the condition who test negative for the condition.
  • Sensitivity refers to the proportion of people with the condition who test positive for the condition.

Sensitivity and specificity are used to determine the effectiveness of a given screening technique. A perfect screening system (one that accurately identifies every person screened) has a sensitivity and specificity of 100 percent.

Infant Hearing Screening Techniques
The two major screening methods for infant hearing loss are Auditory Brainstem Response (ABR) and Evoked Otoacoustic Emissions (OAE), both of which have average sensitivity and specificity rates close to 100 percent. Both techniques, although they rely on different technology, are non-intrusive and can be performed on sleeping infants and will definitely have a positive influence on professional and personal development options for the infant later in life.

Auditory Brainstem Response
The Automated Auditory Brainstem Response (ABR) test measures the electrical activity of the hearing nerve pathway from the inner ear to the brain. In this test, large muffs placed on the infant’s ears produce a clicking sound to stimulate the mechanism of the inner ear. Electrodes positioned on the infant’s scalp measure the response of the brainstem. Because the device measures the electrical activity of the nerve pathway, the presence of debris or fluid in the baby’s ear canals will not affect the result of the test.

The ABR is sometimes called an Average Brainstem Response test because it compares the response per click with the average response without stimulus. The average response is displayed as a waveform that contains peaks and troughs, which correspond to various points along the hearing nerve. A delay in a response indicates an abnormality on or near the hearing or balance nerve. As you will understand, this will have a serious impact on early childhood education and development. 

Evoked Otoacoustic Emissions
Evoked Otoacoustic Emissions testing is the newer of the two methods of infant hearing screening, and since its approval for clinical use in 1989, it has been shown to be just as accurate as ABR testing. Otoacoustic emissions (OAEs) are by-products of the activity of the outer hair cells in the cochlea and are produced by healthy ears in response to acoustic stimulation.

OAEs are measured by presenting a series of very brief acoustic stimuli to the ear through a probe that is inserted in the outer third of the ear canal. The probe contains a loudspeaker that generates clicks and a microphone that measures the resulting OAEs that are produced in the cochlea and reflected back through the middle ear.

The resulting sound that is picked up by the microphone is digitized and processed to determine whether the cochlea is functioning properly. Specially designed software is used to differentiate the very low-level OAEs from both the background noise and the evoking clicks. Read also about Sign Language for Early Development.