Introduction

Hearing impairment during early life interferes with the development of verbal language skill. Significantly reduced auditory input adversely affects development of the auditory nervous system and may have deleterious effects on cognitive and academic development. Thus hearing impairment should be recognized as early in life as possible so that remedial measures can take full advantage of the plasticity of developing sensory system and child can enjoy normal social development.

The overall incidence of severe congenital hearing loss is 1–3 in 1000 live births. However, 2–4 per 100 infants surviving neonatal intensive care have some degree of sensorineural hearing loss [1].

Development of the auditory system starts at 3–6 weeks; by 25 weeks all parts are in-place, though adult dimension is not attained until 1 year after birth [2].

Universal newborn hearing screening is recommended to detect hearing loss as early as possible. Earlier ABR became the procedure of choice for newborn hearing screening [3]. Currently acceptable methods for physiological hearing screening in newborn are evoked otoacoustic emission and auditory brainstem response [4]. A threshold of > 35 dB has been established as a cut off for an abnormal screening which prompts further testing. OAE is quicker, more affordable and less cumbersome and less demanding procedure.

For newborn sensorineural hearing loss, risk factors are family history of hereditary childhood sensorineural hearing impairment, intrauterine infections (TORCH), craniofacial anomalies, birth weight < 1500 g, hyperbilirubinemia requiring exchange transfusion, ototoxic medication, bacterial meningitis, APGAR score 0–4 at 1 min, mechanical ventilation for 5 days or longer and presence of other findings associated with a syndrome known to include hearing loss [5]. The aim of our study was to compare the results of OAE in term and preterm sicknewborns.

Materials and Method

This descriptive study was conducted in SNCU of a tertiary care hospital over 3 month’s period. All newborns (age up to 28 days) admitted to SNCU were included in the study. Newborns with external ear pathology making it difficult to insert a probe were excluded from the study. In the study newborns, distortion product otoacoustic emission (DPOAE) was recorded from both ears at the time of discharge.

Results

In 3 months of the study period, 640 sick newborns were admitted tothe SNCU. Among them 456 were term and 184 preterm. Table 1 shows different pathological conditions in term and preterm babies.

Table 1 Different pathological conditions in term and preterm newborns
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Tables 2 and 3 show number and percentage of “refer” OAE in different pathological conditions in term and preterm newborns respectively.

Table 2 Refer OAE in term newborns
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Table 3 Refer OAE in preterm newborns
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The percentage of observed “refer” results among term and preterm sick newborns were tabulated in Microsoft Excel. Expected values were calculated thereof. p value of Chi square test on these values came to be 0.85.

Discussion

There are several risk factors for hearing impairment in newborns like birth asphyxia, sepsis, meningitis, ototoxic drug use and hyperbilirubinemia needing exchange transfusion [6].

Birth asphyxia is a risk factor for hearing impairment. It can be justified by the fact that due to birth asphyxia there can be intensive para sagittal injury more laterally and posteriorly in the border zone of parieto-occipital lobe which is more severe in pre term newborns [7]. In our study 4.8% term sick newborns and 31.5% preterm sick newborns with birth asphyxia had “refer” on OAE. Septicaemia also causes hearing impairment in newborns. 8.6% term newborns and 32.5% preterm newborns with septicaemia had “refer” on OAE. In newborn hyperbilirubinemia causes hearing loss infrequently due to preventive measures like phototherapy. But newborns who need exchange transfusion are at high risk of hearing loss. Kernicterus causes more damage in asphyxiated, acidotic and premature newborns. They mainly cause high tone loss but less commonly cause profound hearing loss. In our study 25% term and 75% preterm newborns, who received exchange transfusion due to severe hyperbilirubinemia, had “refer” on OAE. Preterm newborns with meningitis also have higher incidence of hearing impairment than term newborns. In our study 22.9% term and 41.7% preterm newborns with meningitis had “refer” on OAE. Premature newborns without other co-morbid conditions have lower risk of hearing impairment. In our study 8.7% got a “refer” on OAE. Prematurity per se is not responsible for hearing impairment. Because the ears are fully developed at the end of 2nd trimester. Risk of hearing impairment increases with co-morbidity of prematurity [8]. In our study we didn’t find any statistically significant difference in the rates of “refer” result on OAE between term and preterm sick newborns. Hence hearing impairment is more of an accompaniment of different pathological conditions but not prematurity.

Conclusion

Sick newborns with co-morbidities like birth asphyxia, sepsis, meningitis, ototoxic drug use and hyperbilirubinemia needing exchange transfusion are more likely to get a “refer” on OAE. But the incidence is not significantly higher in preterm sick newborns with these co-morbidities.