Hearing Screening in High-Risk Neonates Using Distortion Product Oto-Acoustic Emission

Abstract

The prevalence of hearing loss is 0.09–2.3% in low risk neonates, and 0.3–14.1% in the high-risk population. The treatment requires early identification by neonatal hearing screening and early rehabilitation. OAE (oto-acoustic emission) and ABR (Auditory Brain Response) are the two objective tests used to evaluate hearing loss in neonates. OAE tests the biological response of the cochlea to auditory stimuli. ABR tests the auditory pathway. The aim is to estimate hearing loss in high-risk neonates using the Distortion Product Oto- acoustic emission (DP OAE) and to correlate the associated high-risk factors. This was a cross-sectional study conducted between March 2021 to September 2022. Newborns satisfying the inclusion criteria were included in the study. DP- OAE is performed to screen for hearing loss within 48 h of birth. Infants failing the first screening test are then examined for treatable causes and then repeated at 2 weeks. Newborns who fail the second DP-OAE are subjected to ABR for confirmation of hearing loss. A total of 100 high risk neonates underwent hearing screen using DP-OAE. Most common risk factors seen in our study are prematurity (22%), Low birth weight (< 2.5 kg) (20%), Neonatal Hyperbilirubinemia (17%), Maternal risk factors (GDM) (14%). Most neonates with prematurity failed the hearing test with significant p-value of 0.05. DP- OAE test can be successfully implemented as newborn hearing screening method, for early detection of hearing impairment to achieve the high quality standard of screening programs.

Introduction

In the world, India has one of the largest new-born populations where universal hearing screening is an uphill task. The incidence of neonatal hearing loss in India is 1–6 per thousand [1]. Communication is the ‘Key to Life. Communication is easily overlooked, but the ability to communicate effectively is necessary to carry out the thoughts and visions of an organization to the people, to convey directions and provide synchronization. Speech and hearing are interrelated-i.e., a problem with one could mean a problem with the other as speech and language is acquired normally through auditory system [2]. It is important to innovate culturally acceptable ways of implementing newborn Hearing Screening programs [3].

OAE test is the most sensitive test for detecting hearing loss in new born. However, OAE alone cannot be used to confirm a diagnosis of hearing loss. It is usually substantiated with other tests like Brainstem Evoked Response Audiometry (BERA) also known as Auditory Brain Response (ABR) for definitive diagnosis [4].

OAE tests the biological response of the cochlea to auditory stimuli. OAE’s are pre-neural in origin and directly dependent on outer hair cell integrity [5]. BERA measures activity from the auditory nerve up to the level of brainstem on stimulating with acoustic stimulus. It assesses the neural integrity of auditory pathway up to the brainstem. However, it is an indirect measure of hearing acuity [6]. Since hearing plays an important role for children in learning speech and language, socialization and cognitive development This study was aimed to estimate the proportion of hearing loss in high risk neonates and to correlate the risk factors associated with it at tertiary care centre for early intervention.

Materials and Methods

A prospective cross-sectional study done for evaluation of hearing in high risk neonates from March 2021 to September 2022. The high risk factors considered were Prematurity, NICU > 5 days, Low birth weight (< 2.5 kg), Use of ototoxic drugs, Birth asphyxia, Neonatal seizures, Congenital anomalies, Hyperbilirubinemia, Maternal risk factors (TORCH infections and GDM), Family history of hearing loss and history of Consanguinity. Infants on ventilators who were severely ill and had Congenital anomalies of ear were excluded.

After obtaining clearance and approval from institutional ethics committee and written informed consent from parents/ guardian, neonates who fulfilled the inclusion criteria underwent DP-OAE. A composite probe inserted in the external ear canal and auditory stimuli were given in the form of tones. The results were interpreted as either Pass or Refer. Those who had refer in the first screening were followed up for second screening within 2 weeks. Those who had refer at second screening underwent BERA.

Results

Total number of neonates included in the study were 100 (ear studied 200). 53% were males and 47% were females. The male:female ratio is 1.02:1.

The percentage of risk factors seen among study group were 22% of prematurity, 20% of LBW, 9% of birth asphyxia, 14% of maternal diabetics, 1% of congenital anomalies, 17% of hyperbilirubinemia, 6% of family history of hearing loss, and 11% of consanguinity.

1st DP-OAE results showed 76.5% (153 ears) pass. Among 23.5% (47 ears) who were refer and underwent 2nd DP-OAE showed 95.7% (45 ears) pass and 4.2% (2 ears) was refer. BERA was conducted for confirmation of hearing loss. Statistical significance was seen in neonates with prematurity (p = 0.051).

Discussion

Hearing loss has high prevalence and frequently occurring entity which can be overlooked because of its invisible nature. Even though it is not a life-threatening condition, failure to intervene in time renders it a severe threat to critical quality of life indicators, thus making this condition the most prevalent sensory deficit in the population [7]. In India, it is estimated that 18.49 million persons have disability that equivalents to 1.8% of the total population of the country where 10% of this figure are likely to have hearing disability of moderate to profound degree [8]. Moreover, this number is likely to go up if routine early hearing screening is not considered. Therefore, implementation of neonatal hearing screening helps to minimize the hearing impairment and its deficits leading to delay in speech, language, social, emotional and cognitive development of children. Early identification is defined as diagnosis as early as 3 months with intervention by 6 months. However, OAE pass does not always mean the hearing is normal.

Gender Wise Distribution of Patients

Among 100 neonates included in the study with male: female ratio was 1.02:1 which are in co-relation with the studies conducted by Nagapoornima P et al. [9] and Finckh-Kramer U et al. [10].

OAE in Neonates with Prematurity

The premature infants are at risk for developing complications of prematurity like bronchopulmonary dysplasia (BPD), periventricular leukomalacia (PVL), intraventricular hemorrhage (IVH), culture-proven sepsis, retinopathy of prematurity, and patent ductus arteriosus. PVL is characterized by white-matter necrotic lesions, commonly associated with spastic diplegia, seizures, developmental delay, and visual and hearing impairments due to hypomyelination and neuronal death. White-matter abnormalities of the auditory neural pathway can cause SNHL.

In our study there were 22% of premature neonates (44 ears) among which 16 ears had refer results on OAE which was significant. Similar observation of hearing loss with prematurity was seen in study conducted by J Smurzynski et al. [11].

OAE in Neonates with Low Birth Weight

In a study conducted by R Cristobal et al. it was found that hearing loss among LBW infants is a common finding. The presence of SNHL in infants with LBW is unknown but associated factors with LBW such as NICU admission, ototoxic drugs, hypoxia, may lead to progressive hearing loss [12].

Robertson CM et al. found that respiratory distress syndrome has consequences such as an increased exposure to other risk factors such as acidosis, antibiotic courses, prolonged incubator and ventilator noise, which may result in hearing impairment and other neurological impairments [13].

20% of LBW neonates were included in the present study with no statistically significant hearing loss.

OAE in Neonates with Birth Asphyxia

Erik Borg et al., in a study stated that hypoxia is strongly associated with hearing loss, as adequate oxygenation and perfusion are crucial for normal cochlear function. It is known that severe hypoxia may cause irreversible injury to the outer hair cells and stria vascularis in the cochlea, however there is no clear threshold level of hypoxia at which hearing might be destructed [14]. In our study there were 9% Neonates with birth asphyxia with no hearing loss.

OAE in Neonates with Maternal Risk Factors (Torch Infections/ GDM)

Zhou JH et al. stated that GDM is a known risk factor for complications like prematurity, hypoglycemia in the baby, seizures, electrolyte imbalance requiring NICU admission and hindering neuronal development thus leading to hearing impairment [15].

Singh G et al. stated that in congenital infections, the temporal bone has demonstrated inflammation and oedema of the cochlea and spiral ganglion, and viral antigens have been found in the spiral ganglion, organ of Corti, scala media and Reissner’s membrane and direct cytolysis of components of the labyrinth, including hair cells [16]. In the present study, Neonates with maternal risk factors show 0% refer results.

OAE in Neonates with Hyperbilirubinemia

Bilirubin has been recognised as a neurotoxin since the late 19th century. In a study conducted by Boo N Y et al. it is stated that the reported incidence of hearing loss in term neonates, following exposure to severe hyperbilirubinemia, based on auditory brainstem-evoked response (ABR), was as high as 22%. Hyperbilirubinemia could damage outer hair cells of the cochlea and primarily retro-cochlear damage- the brainstem auditory nuclei, auditory nerve and ganglion cells leading to auditory neuropathy [17]. In the present study neonates with hyperbilirubinemia are found to pass on OAE test.

OAE in Neonates with Consanguinity

The prevalence of childhood permanent congenital HL is 1.2 to 1.7 cases per 1000 live births [18]. Study conducted by Almazroua AM et al. states that in a Consanguineous marriage it is more likely to be homozygous for the same trait, and hence more chance of congenital deafness in children [19].

Approximately 70% of prelingual genetic hearing loss is nonsyndromic. Nonsyndromic hearing loss may be inherited in an autosomal dominant manner (19%), with mitochondrial or X-linked inheritance (< 1%). Although autosomal dominant inheritance is the common type [20]. In the present study neonates born in consanguineous marriage did not have hearing loss on OAE test.

OAE in Neonates with Family History of Congenital/ Childhood SNHL

Carlie Driscoll et al. [21] in a study stated that family history is considered a risk factor for permanent congenital, delayed onset, or progressive hearing loss by the Joint Committee on Infant Hearing since 1973. Family history of childhood hearing loss is still considered a risk factor for both congenital and postnatal hearing loss. In the present study, neonates with family history of congenital/ childhood SNHL show 0% refer results on OAE test.

OAE in Neonates with Congenital Anomalies

Koffler T et al. [22], states that congenital anomalies with hearing loss are best categorized by mode of inheritance, which can be autosomal recessive (AR), autosomal dominant (AD), or X-linked. The 3 major syndromes associated with an AR inheritance are Usher syndrome, Pendred syndrome and Jervell and Lange-Nielsen syndrome.AD syndromes associated with hearing loss are Waardenburg syndrome, Treacher Collins syndrome, Stickler syndrome, branchio-oto-renal syndrome (Melnick-Fraser syndrome), neurofibromatosis type 2, osteogenesis imperfecta. The X-linked syndromes associated with hearing loss are Alport syndrome, Norrie syndrome, and oto-palato-digital syndrome. In the present study only 1 neonate with congenital anomaly of cleft palate was examined and had no evidence of hearing loss.

Conclusion

Universal hearing screening protocols are difficult to follow due to large population and lack of awareness. Children with hearing loss may be missed and may present late when it affects child’s communication abilities. The present study concludes that the DP- OAE test can be successfully implemented as newborn hearing screening method, for early detection of hearing impairment on a large scale to achieve the high quality standard of screening programs. Also, it is good practice to combine OAE and BERA for screening hearing loss in high risk neonates. Early detection will facilitate prompt intervention so that child will be ensured with adequate development of language and good cognitive functions. Failure to detect early leads to significant delay in speech development, social cognitive and emotional development. This study not only contributed towards early assessment and intervention but also made a greater public awareness among parents in the early neonatal hearing assessment.

Fig. 1.

1st DP-OAE results of right ear

Fig. 2.

1st DP-OAE results of left ear

Table 1.

Demographic analysis – Gender distribution of the risk factors

Sl. no	High risk factors	Male	Female	Total
1	Prematurity	10%	12%	22%
2	NICU > 5 days	0%	0%	0%
3	Low birth weight (< 2.5 kg)	10%	10%	20%
4	Use of ototoxic drugs	0%	0%	0%
5	Birth asphyxia	6%	3%	9%
6	Neonatal seizures	0%	0%	0%
7	Maternal risk factors (TORCH infections and GDM)	8%	6%	14%
8	Congenital anomalies	1%	0%	1%
9	Hyperbilirubinemia	9%	8%	17%
10	Family history of hearing loss	2%	4%	6%
11	Consanguinity	7%	4%	11%
	Total	53%	47%	100%

Table 2.

DP-OAE results of 1st and 2nd visit

OAE	Pass N (%)	Refer N (%)
1st OAE results –Right	75 (75%)	25 (25%)
1st OAE results –left	78 (78%)	22 (22%)
2nd OAE results –Right	24 (99%)	1 (1%)
2nd OAE results- left	21(99%)	1 (1%)

1st DP-OAE results show 75% pass and 25% refer in right ear and 78% pass and 22%refer in left ear.

2nd DP-OAE results show 99% pass and 1% refer in both ears which was confirmed by BER.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Dr. J SARAH BAI, Dr. PRAJWAL GOWDA P R. The first draft of the manuscript was written by Dr. J SARAH BAI and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

The authors have no relevant financial or non-financial interest to disclose.

Data Availability

The data used in this study was not used/published in any other publications.

Code Availability

The data was compiled and analyzed using Microsoft excel version 10.

Declarations

Conflict of interest

The Authors declare that there is no conflict of interest.

Ethics Approval

The study was done after approval of the Institutional Ethics committee from The Oxford Medical College & Research Centre, Bangalore, Karnataka, India in accordance with ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Consent to Participate

Written informed consent was taken from all the parents/guardians of the neonate.

Consent for Publication

All authors have reviewed the manuscript and approved the version to be published.