KOCHI: The first year of life is a critical period for brain development in babies, especially that of the hearing pathway. Auditory experience during this period has a profound influence on the functional development of the auditory system. A lack of the same can have detrimental effects, as can be understood by this basic neurodevelopmental phenomenon.
At birth, the brain has 100 billion neurons (nerve cells) and they form about 50 trillion connections. The only way the connections can be strengthened is by stimulation – both auditory and sensory, and those that aren’t withering away. So, constant auditory stimulation is vital for optimal development of the auditory system, a prerequisite for optimal development of speech and language.
Even mild hearing loss, if not detected, early can significantly retard the acquisition of language skills. Untreated hearing loss of a greater degree has a measurable, even devastating effect on speech and intellectual development.
The incidence of hearing loss is found to be in the range of 1-2 per thousand in the general population. This is quite high as compared to all other screenable diseases put to gather (thyroid disorders, sickle cell anaemia or phenylketonuria). In high-risk babies (babies with a birth weight of fewer than 1500 gms, given artificial ventilation for more than five days, with high bilirubin levels, meningitis, birth asphyxia, ototoxic medications or family history of hearing loss, intrauterine infections, craniofacial anomalies) the incidence of hearing loss is 10-20 times higher.
Diagnosis
Oto Acoustic Emission (OAE) test is the most widely used screening test carried out on babies shortly after birth. It’s a portable tiny piece of equipment (weighing 150 gms). A small earpiece (containing a speaker and microphone) is placed in the child’s ear. A click sound is played and if the cochlea is working properly, the earpiece will pick up the response.
A poor response to an OAE does not necessarily mean that the child is deaf. Background noise, an unsettled body, fluid in the ear from birth, cerumen in the ear canal, non-aeration of the middle ear — all can give abnormal results. In that case, the test must be repeated after four weeks. If the test shows abnormalities still, an ABR test is done for confirmation.
Early detection
If a hearing problem exists, it should be detected and remediated at least by the time the child is six months old so that language development will occur normally. If detection and remediation are done after one year, language development will be adversely affected. If it’s done after 2-3 years, the child will become deaf-mute.
If we detect hearing loss before 3 months and remediate it before 6 months, the condition will improve with a hearing aid alone and may not require an expensive cochlear implant.
For the first time in the country, the Indian Academy of Pediatrics, Kochi initiated Centralized Newborn Hearing Screening in 2003 in all 32 hospitals in the city. Subsequently, the programme was expanded to the entire district in 2014 and the entire state in 2020. This successful Kochi model is now being replicated across the country and appreciated by WHO.
The author is a chief paediatrician at Indira Gandhi Co-operative Hospital, Kochi