Congenital Sensorineural Hearing Loss (SNHL) is estimated to be 1.5-6 per 1000 livebirths.'The prevalence of congenital SNHL is 2-3 per 1000 live births in India.^[1] A child withcongenital deafness may appear normal until few years of age, when parentsrecognize the condition and approach the otorhinolaryngologist. Deafness diagnosed andmanaged before the age of 6 months develop superior language and cognitive skills whencompared with those diagnosed after 6 months.^[2] So, early diagnosis and treatment is essentialfor normal speech and language development in an infant with hearing loss.

Development of inner ear and functional auditory brainstem pathway is completeseveral weeks before the birth. A normal newborn can process the sound and accuratelyanalyse the loudness and pitch of the sound. Localization of the sound discrimination of thespeech occurs in early infancy. Infants with hearing thus learn to process speech understandlanguage by 1 year of age. When there is deprivation of the sensory input, morphological andfunctional properties of neuron breakdown. Reintroduction of the sensory stimulationduring this period can ameliorate the deleterious effect.In the absence of early recognition, a child who is deaf or hard of hearing in infancy, can experience delays in speech andlanguage development, academic achievement, and social and emotional outcomes.^[3]

Until the1990s, the average age of identification for children with permanent hearing loss was 2-3years of age. Due to the proliferation of newborn screening programs, the average age ofhearing loss identification has decreased to 2 to 3 months of age.^[4]In most cases, hearing loss is non-syndromic in nature, and most commonly, there areno outward signs of the disorder. The reasons for this are that children remain very motivatedto connecting with their environment and those around them. Even in the complete absenceof hearing, they have a remarkable ability to use social cues associated with vision, and othersensory cues in their environment, to respond in ways that make it difficult for theircaregivers to perceive the hearing loss. This can be compounded by caregiver denial that thereis a sensory deficit with their child. As a result, the most common indicator of hearing lossbefore infant hearing screening was failure to develop language.

In the absence of screening,the age of detection for severe to profound SNHL ranged between 2 and 3 years of age.^[4]Given late identification of hearing loss, the hard work ahead is both learninglanguage and catching up. Missing the window of language learning means that manychildren with hearing loss never do catch up. The median reading level for a child withbilateral deafness graduating from high school was fourth grade.^[5] It is known that earlyaccess to language through appropriately fit hearing-assistive technology or early exposure tofluent sign language (via deaf parents who are fluent signers) provides dramatic benefits forlanguage and literacy and also can eliminate other pitfalls such as social isolation, feelingawkward with peers, immaturity, physical, social, emotional and sexual abuse, depressionand psychiatric disturbances. Hence, all these make hearing loss an ideal disorder to subject to ascreening protocol.Congenital hearing loss can be inherited as a familial disease / syndrome which runs infamilies or may occur because of any perinatal insult. Hereditary SNHL is of two types -syndromic & non-syndromic disorders. Of these, 18-20% are autosomal dominant and 80%cases are autosomal recessive.^[3]Sex-linked inheritance accounts for 6% males andmitochondrial inheritance of genetic deafness represents 1-2% of diagnosed cases.

The prenatal period is a time of complex embryogenesis and fetal development. Infections ofthe mother during pregnancy such as TORCH (toxoplasmosis, CMV, syphilis, rubella,herpes) all have been associated with congenital SNHL.^[6,7] Also gestational diabetes &hypothyroidism in mother during pregnancy, maternal habits like alcohol may contribute tocongenital SNHL.^[3]Prenatal exposure to tobacco, illicit drugs, certain medications likeaminoglycosides, macrolide antibiotics, loop diuretics, certain chemotherapeutic agents(platinum-containing, such as cisplatin and carboplatin) can be damaging to the newbornfetus.^[8]After birth, hypoxia and anoxia has been associated with SNHL. Hyperbilirubinemia(>20mg/dL) may affect both cochlea and retro-cochlear pathways.^[9]Apgar score < 5 at 1 min&<7 at 5 min is a risk factor for hearing loss.^[3]Otoacoustic Emissions (OAE) test is recommended for neonatal hearing screening as it isobjective, easy, less expensive and lesser time consuming (3-5 minutes). Both TE (Transientevoked) OAE & DP (Distortion product) OAE can be used for screening purpose. In thecurrent study, Distortional Product OAE (DPOAE) was used for neonatal hearingscreening. As it uses high frequency (2 kHz to 8 kHz), it is more suitable as a screening toolin neonatal units and out-patient departments where there is some environmental noise. Also, it has significantly better diagnostic accuracy when compared to Transient Evoked OAE(TEOAE) which requires noise proof settings.

The study aimed to implement a neonatal hearing screening program using otoacoustic emissions at Northern Railway Central Hospital, New Delhi, to assess the incidence of neonatal hearing loss, determine the prevalence of hearing loss in high-risk neonates, and identify risk factors associated with hearing loss in newborns

Conducted over 18 months, from September 2019 to May 2021, the prospective observational study involved neonates born at the hospital and those attending the ENT and Pediatrics Outpatient Clinics without prior hearing evaluations. The inclusion criteria encompassed all neonates born at the hospital, those visiting the outpatient clinic, and newborns who failed initial hearing screenings. Exclusion criteria included infants less than 24 hours old due to the risk of false negatives, infants whose parents refused consent, and those lost to follow-up.

The required sample size was estimated at 987 based on an incidence of congenital sensorineural hearing loss of 3.4 per 1000 live births, but due to the COVID-19 pandemic, only 250 cases were available for analysis. Informed consent was obtained from parents, and a detailed neonatal profile was recorded, including demographic data and patient history. Risk factors were assessed based on the High-Risk Registry of the Joint Committee on Infant Hearing, focusing on prenatal and perinatalhistories, as well as family history of hearing loss. Neonates were classified as high-risk based on specific criteria such as family history of congenital deafness, maternal smoking or alcohol use during pregnancy, and gestational complications. An otoscopic examination was performed to assess ear anatomy, and initial screening was conducted using otoacoustic emissions in a quiet room, ensuring the external auditory canal was clear. Follow-up testing was done at three and six months for those who did not pass the initial screening. Further audiological assessments, including behavioral observation audiometry, impedance audiometry, auditory brainstem response, and auditory steady state response was done (who did not pass the initial screening) to confirm the diagnosis of congenital deafness. Statistical analysis was performed using SPSS software, presenting quantitative variables as mean ± SD or median, while categorical variables were expressed as frequencies and percentages, with appropriate statistical tests applied to determine significance.

In the bilateral pass group, there were 114 males (49.4%) and 117 females (50.6%). In contrast, the bilateral refer group consisted of 5 males (35.7%) and 9 females (64.3%). Regarding family history, 3 neonates (1.3%) passed the screening, with no referrals recorded. For consanguinity, 11 neonates (4.8%) passed the screening, and 1 (7.1%) was referred.

In the ototoxic drugs category, 1 neonate (0.4%) passed, with no referrals noted. Among neonates with gestational diabetes mellitus, 5 (2.2%) passed, and 1 was referred. For gestational hypertension, 15 neonates (6.5%) passed, and 1 was referred. In the hypothyroidism group, 27 neonates (11.7%) passed, and 3 (21.4%) were referred.

Regarding the mode of delivery, in the vaginal delivery group, 100 neonates (43.3%) passed, while 6 (42.9%) were referred. In the LSCS group, 131 neonates (56.7%) passed, and 8 (57.1%) were referred.

In terms of birth weight, the mean for the bilateral pass group was 2.96 kg (SD 0.43), while the bilateral refer group had a lower mean of 2.67 kg (SD 0.52). The bilateral refer group also showed a mean birth weight of 2.40 kg (SD 0.77) for neonates with left refer and right pass, and 2.90 kg for those with right refer and left pass. The median birth weight for the bilateral pass group was 2.9 kg (IQR 2.7–3.2), and for the bilateral refer group, it was 2.6 kg (IQR 2.31–3.09). The range for the bilateral pass group was 1.2 to 4.25 kg, compared to 1.8 to 3.6 kg for the bilateral refer group.

Low birth weight was observed in 26 neonates (11.3%) in the bilateral pass group and 6 (42.9%) in the bilateral refer group, with 3 (75.0%) in the left refer and right pass group, and none in the right refer and left pass group. Prematurity was noted in 20 neonates (8.7%) in the bilateral pass group and 8 (57.1%) in the bilateral refer group, including 2 (50.0%) in the left refer and right pass group, and none in the right refer and left pass group.

For the APGAR score at 1 minute, the mean score was 7.90 (SD 0.36) in the bilateral pass group and 7.43 (SD 0.76) in the bilateral refer group. The left refer and right pass group and the right refer and left pass group both had a mean score of 8.00. The median APGAR score for the bilateral pass group was 8 (IQR 8–8), while for the bilateral refer group, it was 8 (IQR 7–8).

At 5 minutes, the mean APGAR score for the bilateral pass group was 9.09 (SD 0.40), while it was 8.64 (SD 0.50) for the bilateral refer group. Both the left refer and right pass group and the right refer and left pass group had a mean score of 9.00. Median scores were 9 (IQR 9–9) for both groups.

Regarding birth hypoxia, 5 neonates (2.2%) in the bilateral pass group were affected, compared to 4 (28.6%) in the bilateral refer group. In the high-risk category, 87 neonates (37.7%) in the bilateral pass group were classified as high risk, compared to 12 (85.7%) in the bilateral refer group, including 3 (75.0%) in the left refer and right pass group, and none in the right refer and left pass group. (Table 1)

Table 1: Demographic and Clinical Characteristics of Neonates Based on Screening Outcomes (n=250)

231 (92.4%) of the participants had OAE (1 Week): B/L Pass. 14 (5.6%) of the participants had OAE (1 Week): B/L Refer. 4 (1.6%) of the participants had OAE (1 Week): L -Refer, R -Pass. 1 (0.4%) of the participants had OAE (1 Week): R-Refer, L-Pass.

7 (70.0%) of the participants had OAE (3 Months): B/L Pass. 3 (30.0%) of the participants had OAE (3 Months): B/L Refer.

4 (80.0%) of the participants had OAE (6 Months): B/L Pass. 1 (20.0%) of the participants had OAE (6 Months): B/L Refer

Table 2: Results of OAE

The one participant who had bilateral ‘refer’ OAE at 6 months underwent a detailed Auditory Workup.

The present study was conducted in the Department of ENT in collaboration with the Department of Pediatrics at Northern Railway Central Hospital, New Delhi. It involved 250 neonates, including both in-hospital deliveries and those delivered elsewhere, who attended the Outpatient Clinic of the ENT department. This was a prospective observational study carried out over 18 months, between September 2019 and May 2021. Due to the impact of the COVID-19 pandemic, routine outpatient services were suspended for significant periods at our hospital. Additionally, the number of deliveries was drastically reduced, as a large portion of the hospital was converted into a COVID-19 facility. These extraordinary circumstances meant that only a small sample of 250 cases could be included.

The aim of the study was to determine the incidence and prevalence of hearing loss in newborns and to identify the risk factors for congenital hearing loss.

The 250 neonates in the study were initially screened for hearing loss between 24 hours and 7 days of age. A total of 19 (7.6%) neonates had a "refer" result in either ear during the first stage of screening. Among these, 18 had a "refer" result in the left ear, and 16 had a "refer" result in the right ear.

The 19 neonates with "refer" results in the first screening were re-screened at 3 months of age using the same OAE test. Of these, 3 had a "refer" result in both ears, while 7 were lost to follow-up. The remaining 9 neonates had a "pass" result in both ears.

The 3 neonates who still had "refer" results at 3 months were tested again at 6 months of age. Two of them showed a "pass" result in both ears, and 1 had a "refer" result in both ears. Upon further detailed audiological evaluation, the one neonate who had "refer" results was found to have normal hearing.

FACTORS AFFECTING OAE RESULT AND HEARING LOSS

Gender
There were 121 male and 129 female neonates included in the study. Among these, 8 male neonates showed a bilateral "refer" result, while 9 female neonates had a bilateral "pass" result during the initial screening. Additionally, 2 male and 2 female neonates showed "refer" results only in the left ear, while 1 female neonate showed a "refer" result in the right ear. In follow-up at 3 months of age, 3 female neonates showed bilateral "pass" results, and 4 male neonates showed bilateral "pass" results. One male and one female neonate had bilateral "refer" results. At 6 months, 1 male and 1 female neonate showed bilateral "pass" results, while 1 female neonate continued to have a bilateral "refer" result, but she was later found to have no hearing loss. Seven neonates (2 male, 5 female) were lost to follow-up.

In a study conducted by G. Mishra et al. (2003), a male-to-female ratio of nearly 3:2.5 was observed. However, the authors stated that hearing loss is not a sex-linked disorder and does not exhibit gender predisposition, though such data is essential for epidemiological purposes.^[10]
Hasan Ibrahim et al. screened 1413 babies for hearing impairment in their study. Among them, 733 infants were male, and 680 were female. They found that 96.8% (1368 out of 1413) of babies passed the first OAE, while 45 babies (30 girls and 15 boys) ie 3.2% did not pass the first OAE in one or both ears. Their findings showed a statistical correlation between gender and passing the OAE test (P-value = 0.01), with females showing a higher rate of failure during the first screening.^[11]

High-Risk Category

In the study, 91 (36.4%) neonates were categorized as high-risk. None of these neonates was found to have hearing loss. These 91 high-risk neonates were further divided based on risk factors, including prenatal risk factors, significant family history, and postnatal risk factors. Among the 58 babies with prenatal risk factors, none showed hearing loss. Of the 3 babies with a family history of hearing loss, all passed the initial screening. Among the 30 babies with postnatal risk factors, none were found to have hearing loss. 16 mothers had a history of gestational hypertension. Out of which, only 1 (6.25%) baby showed ‘refer’ result during initial screening, which eventually had ‘pass’ result during third-time screening. None of them had hearing loss.

According to a study by Zhou et al. (2003), the "refer" rate was 4.5% in mothers with gestational diabetes, compared to 1.7% in mothers without gestational diabetes.^[12]

Another study by Oppy Surya Atmaja et al. examined preeclampsia as a risk factor for cochlear damage. Among the preeclampsia group, 10% of patients showed a "refer" result, while all patients in the normal pregnancy group showed a "pass" result.^[13]

TORCH Infections

In the present study, none of the mothers had TORCH infections during pregnancy.

Hypothyroidism
Among the 30 mothers with a history of hypothyroidism, 3 (10%) babies had a "refer" result during the initial screening. Two of these babies were later found to have a "pass" result at follow-up screenings at 3 and 6 months. One baby was lost to follow-up, and none of the babies in this group had hearing loss.

Ellen E. Wassennann et al. noted that maternal hypothyroxinemia can impair the development of the inner and middle ear during the first and early second trimesters, leading to potential hearing loss in children.^[14]

Family History and Consanguinity

Of the 12 mothers with consanguineous marriages, 1 (8.3%) had a baby with a "refer" result during the initial screening, but the baby passed the second screening. None of the babies born to consanguineous parents were found to have hearing loss. Additionally, 3 mothers reported a family history of hearing loss, and all their babies passed the initial screening.

Hasan Ibrahim et al. found a higher rate of failure in babies with a family history of congenital hearing problems (18.9% failure rate) compared to those without such a history (2.5%).^[11]

In contrast, Nagapoornima et al. reported that 94% of cases of hearing loss in their study did not have a significant family history of childhood hearing loss.^[15]

Mode of Delivery

There were 107 vaginal deliveries in the study. Of these, 6 (5.6%) babies had a "refer" result in the first screening. Out of these 6 babies, 3 of them showed ‘pass’ result during the second screening and 1 showed ‘pass’ result during the third screening. Rest 3 babies were lost to follow-up. There were 143 cesarean section deliveries, and 12 (8.4%) of these babies had a "refer" result in the first screening. Six of these babies had a ‘pass’ result in the second screening and two babies had a ‘pass’ result in the third screening. Four of these babies were lost to follow-up, but none were found to have hearing loss in subsequent screenings.

In their study on 1413 newborns by Amjad Nuseir et al. found that vaginally delivered (VD) infants had a 1.5-fold higher failure rate for the first OAE test than cesarean-delivered (CD) infants, although this was not statistically significant.^[11]

Prematurity
Out of 250 neonates, 30 (12%) were identified as premature. Ten of these babies had a "refer" result in the initial screening.Out of these, two babies continued to have a "refer" result at the second and third screenings, while 6 were lost to follow-up. None of the babies followed up were found to have hearing loss.

Eline S. Marlow et al. (2000) found that preterm children with SNHL often require more intensive care during the perinatal period and experience more neurological complications compared to controls. The coexistence of risk factors in preterm babies was found to be more important than individual factors alone.^[16]

Hyperbilirubinemia
Eighty neonates had hyperbilirubinemia. Seven (8.8%) of these neonates had a "refer" result during the initial screening. Five were lost to follow-up, while the remaining 2 had a "pass" result in subsequent screenings. None of the neonates with hyperbilirubinemia had hearing loss.

Shapiro et al. suggested that hyperbilirubinemia can cause damage to brainstem auditory nuclei, leading to delayed auditory brainstem response (ABR) latencies.^[17]

Birth Weight

Of the 250 neonates, 35 (14%) had low birth weight, and 215 had normal birth weight. Nine (25.7%) low birth weight neonates had a "refer" result during the initial screening. None were found to have hearing loss in follow-up screenings.

John et al. (2009) identified low birth weight as a common risk factor in high-risk babies, accounting for 56.5% of cases in their study.^[18]

Birth Hypoxia

Out of 250 neonates, 9 (3.6%) had a history of birth hypoxia. Of these, 5 had a "pass" result in the initial screening. One neonate was lost to follow-up, but no hearing loss was detected in the babies who were followed up.

Zia Ul Haq Gouri et al. observed that neonatal hypoxia, jaundice, prematurity, and prolonged NICU stay were present in 12% of cases, contributing to the incidence of hearing loss.^[19]

Congenital hearing loss is an entity of very less common occurrence.The present study revealed that OAE test has a false positive rate of 7.6%.It also concluded that asingle OAE test wasnot enough as a screening tool for congenital deafness, as infants screened during the initial stage who had a'refer’ resultat 1month, turned out to be 'pass' at 3months&those who were still 'refer' at 3 months got a "pass' result at 6 months. This led us to the conclusion that the 1-3-6 principle must be followed very strictly for infant screening.It was also concluded that even after using the 1-3-6 principle of OAE screening, there was very high chance of false positivity of screening tool. Thus it calls for all such children testing positive by OAE even at 6 months, should be mandatorily undergo an audiological test battery and the OAE test cannot be relied upon as a foolproof tool to label a child as congenitally deaf.

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