Identification of hearing loss in newborns by transient otoacoustic emissions

1. Introduction 

Universal newborn hearing screening is a method to identify, as early as possible, congenital deafness and hearing loss.

When hearing loss is missed in the neonatal period, it is generally not identified until the child is 30 months old. This has a profound impact on speech—language development and later school performance, because the child will not have been able to hear adequately during the most critical period of brain growth and language development [4]. In some countries screening is only done unilaterally [1] or additional diagnostic tests are performed only in those newborns who did not pass the hearing screening bilaterally. Thompson and co-authors in a critical review observed that the same screening also identifies infants who have mild and unilateral hearing impairment, but the consequences of delay are not well established in these infants, and that most are not candidates for hearing aids or other therapies associated with early identification [11]. This contribution will describe the purpose of additional diagnostic tests in those newborns who do not pass hearing screening unilaterally by TEOAE, using as examples two newborn from our study who were identified with deafness and received cochlear implants.

2. Material and methods 

Transient otoacoustic emissions (TEOAE) were obtained bilaterally from 3048 newborns in all newborn patients born in two Gynecology and Neonatology Departments in Bratislava and the Department of Pathological Newborn and Intensive Care Unit of Children's University Hospital in Bratislava where pathological newborns from Slovakia are treated.

The ILO 88 Otodynamic Analyser was used to acquire transient evoked emissions. The newborn hearing screenings were done in two Otolaryngology Department on 4th–12th day after delivery when the newborns were dismissed, or the newborn was transferred to the Department of Pathological Newborn and Intensive Care Unit at our Children's University Hospital. Screening tests were performed by two well-trained specialists. Those newborns who did not pass uni or bilaterally were rescreened by TEOAE 1 month later. Among 3048 newborns, there were 1355 with a risk of hearing loss and 1633 without a risk of hearing loss in the history. All newborns who had not passed TEOAE in the 2nd screening (uni or bilaterally) underwent additional audiologic tests: tympanometry and Brain Stem Response Audiometry (BERA).

3. Results 

The results of screening are summarised in Table 1.

Table 1. Results of newborn hearing screening by TEOAE

	All newborn	TEOAE present	TEOAE not present
	3048	2898	150 newborn (4.9%)
			Unilateral			Bilateral
			74			76
	2nd. examination		Present	Didn't come	Not present	Present	Didn't come	Not present
	TEOAE		47 (31.3%)	18 (12%)	9 (6%)	44 (29.3%)	11 (7.3%)	21 (14%)

Of 150 newborns who did not pass, 74 had absent TEOAE unilaterally and 76 bilaterally. Of these 150 newborns, 29 (19.3%) did not pass (18 unilaterally and 11 bilaterally), 91 (60.7%) passed and 30 (20%) did not pass in the second screening (Table 1).

In all 30 newborns who had absent TEOAE (9 unilaterally and 21 bilaterally) had additional audiologic tests performed: tympanometry and BERA, to confirm or exclude hearing loss.

In nine newborns with unilaterally suspected hearing loss two were false positive (normal hearing), two had unilateral conductive hearing loss, three had unilateral sensorineural hearing loss (2 moderate and 1 deaf ear) and in two newborns bilateral deafness was confirmed (Table 2).

Table 2. Determination of hearing loss (HL) in newborn with unilateral not present TEOAE by additional audiologic tests

	Bilateral deafness	2 (22.2%)
	Unilateral sensorineural HL or deafness	3
	Unilateral conductive HL	2
	Normal hearing	2
	Two times not present TEOAE unilaterally	9 newborns

Case 1 is a female, birthweight 3650 and APGAR score 7/10, mild asphyxia, 2 days of oxygen therapy. Two days later a jaundice developed (bilirubin 324 μmol/l) which ameliorated with phototherapy. On the 10th day the patient was discharged, and OAE on the right side were present and on the left side not present. OAE were rescreened 3 times, with finding of typanometry curve A. When the patient was 6 months old BERA confirmed deafness, with bilateral absence of response. She received hearing aid and logopedic rehabilitation. At 24 months of age the BERA was the same and also TEOAE were present on the right side, CT showed normal cochlea bilaterally and, cochlear implantantion was performed on the left side.

Case 2 is a female, birthweight 3510 g, APGAR score 10/10. No disorders were present during the pregnancy, no history in family for hearing loss. TEOAE presented unilateraly and BERA showed deafness. At 22 months of age cochlear implantation were performed.

From 21 (14%) newborns with absent TEOAE bilaterally five were false positive (normal hearing), two had not yet had BERA examination, five had moderate sensorineural hearing loss bilaterally and in nine profound hearing loss (90–100 dB) or deafness was confirmed (Table 3).

Table 3. Determination of hearing loss (HL) in newborn with bilateral not present TEOAE by additional audiologic tests

	Bilateral deafness or profound HL	9 (42.8%)
	Bilateral moderate sensorineural HL	5 (23.8%)
	Not yet BERA, tympanometry A	2 (9.6%)
	Normal hearing	5 (23.8%)
	Two times not present TEOAE bilaterally	21 newborns

Two cases of deafness in the newborns were siblings, both male, and both had parents with congenital deafness. The parents refused cochlear implantation and both children are in kindergarten for children with hearing loss. Two other deaf newborns had both parents with deafness and one of these has also other members in the family with deafness; this patient will receive cochlear implantation. One deaf boy had congenital deafness in the family (uncle), one deaf girl was without any risk, and both of these received a cochlear implant before the 3rd year of age. Two newborns have CNS pathology (hydrocephalus, hypoxical encephalopathy) and one of these is deaf and the other has profound hearing loss (70–80 dB bilaterally); his mother was ill during pregnancy and received antibiotic treatment. Moderate bilateral sensorineural hearing loss occurred in five newborns, two were without any risk of history and three others had a history of hypoxia, more than 5 days ventilation, and one was also premature with low birthweight 1800 g (Table 4). Five newborns had normal hearing.

Table 4. Etiology of bilateral deafness or hearing loss

	Etiology of bilateral deafnes or hearing loss	No. newborns
	Parents or family deafness/HL	5
	CNS pathology	2
	Mother's illness in pregnancy	1
	Jaundice	1
	Prematurity, ventilation more than 5 days	3
		12

Among 3048 newborns there were 1355 with a risk of hearing loss and 1633 without risk of hearing loss in history. In 11 newborns deafness was confirmed and five had a bilateral sensorineural hearing loss in the range of 45–65 dB (Table 5). The incidence of the children having bilateral profound hearing loss or deafness was higher than in the previous study: this is due to the fact that some newborns with risk of the hearing defect were sent to us from the other hospitals, where hearing screening has not yet been instituted.

Table 5. Bilateral deafness or sensorineural hearing loss (SNHL)

	All newborn	3048	Bilateral deafness	Bilateral SNHL
	Newborn with risk of hearing loss	1355	9	3	12
	Newborn without risk of hearing loss	1663	2	2	4
			11	5	16

All newborns with hearing loss or deafness received hearing aids and started logopedic rehabilitation before 7 months of age and if cochlear implants were indicated the infants received or will receive the implant before 3 years of age, except in the cases of two siblings in which the deaf parents refused cochlear implant.

4. Discussion 

The early identification and diagnosis of hearing impairment in children is the subject of a large number of studies [1], [2], [4], [5], [6]. Transient otoacoustic emissions fill most protocols as non-invasive, time saving and easy to apply and for these reasons has been proposed as the first line screening technique [7], [8], [9], [10]. Targeted neonatal hearing screening programs based on TEOAE can expect to identify hearing impairment in approximately 80% of babies screened [7]. The cause of false negatives is a matter for conjecture. There may be several reasons: the test may give an incorrect results: there may be a later acquired hearing impairment or there may be a progressive hearing loss of unknown origin [7] or there may be central deafness [12]. Purely retrocochlear lesions are encountered rather rarely in a high risk population but should be taken into consideration, especially in cases with positive history of CNS pathology: intracranial haemorhage, hydrocephalus, hyperbilirubinemia [8] and other pathological developments during the neonatal period involving hypoxia [3]. Some investigators recommend universal hearing screening unilaterally [1], some recommend for the second screening and additional audiologic assessment only these newborns who did not pass bilaterally [2], because the consequences of delay are not well established, when the child passes unilaterally—normal hearing may be present [11]. Some authors suggest that the newborn with unilaterally hearing loss is not a candidate for hearing aids and other treatment [11] We have found two newborns who pass unilaterally and only BERA confirmed deafness: on the one side cochlear and on the other side retrocochlear; both patients received cochlear implants. In one of these patients, no disorders were present during the pregnancy, and no history of family hearing loss was present.

Screening tests for hearing impairment can improve identification of the newborns with permanent hearing loss, but 10% of newborns with normal hearing will require a second screening; from 1 to 3% of newborns will be referred for additional audiological assessment [11]. In our study 3% of newborns with normal hearing required the second screening, 1% required the additional audiologic tests; in 2.3% (7 newborns) false positive test results were obtained.

Some of the newborns who did not pass screening will not come to the second screening: also in our study 11 newborns (7.3%) who did not pass bilaterally did not come to the second screening. Newborn hearing screening has been proposed as a means to speed diagnosis and treatment for moderate to profound, bilateral permanent hearing loss and thereby improve language outcomes in these children. When the newborn has an absent TEOAE uni or bilaterally, we must inform the parents and recommend the additional screening and other audiologic tests for confirmation or exclusion of hearing loss.