Currently, all newborns in California born in hospitals undergo universal newborn hearing screening. This testing was phased in during 1999 and became universal as of late 2002. Now, prior to leaving the hospital, all parents should be given a report of whether their child passed hearing screening in both ears, or is being referred to retest one or both ears. This screening was initiated after studies revealed that approximately 3 in 1000 infants demonstrate detectable hearing loss at birth. Multiple sources support that the earlier hearing loss is detected and active interventions are begun, the better a child will respond and function.
There are two main tests that are used to detect hearing loss in newborns. The first is known as OAE, short for otoacoustic emissions testing. This screen is performed by placing small probes in an infant’s ear canal and then stimulating the infant by providing sound through modified loudspeakers. In an unobstructed outer ear canal with a middle ear canal that is clear of fluid, a newborn infant’s cochlea should generate sound that is recorded on a microphone located on the probe sitting within the infant’s ear. This response can be affected by any ear anatomical abnormality or presence of fluid. There are levels of response that are considered standard and each individual infant’s response is measured against this standard.
The second tool used for universal newborn screening is referred to as ABR or auditory brainstem response testing. This procedure is performed in a different manner than OAE testing. ABR is an electrical response versus the sound response measured by OAE screening. Therefore, newborns are fitted with several electrodes placed over the scalp that are set to measure electrical signals. These electrical signals should be generated by the auditory system in response to sound. During ABR testing an earphone is placed in each ear of the newborn infant and sounds are played. Typically, these are a series of clicks at varying frequency levels. A computer that compares the infant’s signal response to a range of known normals then interprets the electrical signals detected by the electrodes.
Both OAE and ABR screening exams are better at detecting mid to high frequency hearing losses versus low frequency hearing losses. This is not considered a significant downfall for either exam as the majority of permanent hearing losses is more likely to be at the mid to high frequency rang. ABR testing tends to be a more expensive test with fewer artifacts than OAE. Middle ear fluid and remnants of an infant’s passage through the birth canal can affect the accuracy of OAE testing. This is due to the necessity of the cochlear sound response passing through the middle and external auditory canals prior to its recording.
Often OAE is used as a first screen. If failed, ABR testing is implemented. Should an infant fail the first testing session this does not necessarily mean there is a clear permanent hearing loss. After screening, infants who fail are referred to outpatient centers for repeat testing usually within weeks of discharge from the hospital. Many infants pass this subsequent screen. Those who do not pass a second battery of tests are scheduled for follow-up. They are tested at variable intervals during the first few months of life in order to give families the most information possible over the child‘s ability to hear.
Generally, the earliest interventions made for detectable hearing loss do not occur until approximately six months of life. With the advent of cochlear implants many infants who would have gone on to be deaf children now are able to participate at normal grade levels without modification of classroom style or learning method.
New parents should be aware of the benefit and assurance of having their new infant screened for hearing loss at birth. This result should be provided in conjunction with newborn screening results such as PKU testing. For more information on California’s newborn universal screening and intervention program check www.infanthearing.org/states/california.