Iran Red Cres Med J. 2014 January; 16(1): e6812.

DOI: 10.5812/ircmj.6812
Research Article

Published online 2014 January 5.

Assessment of Hearing Loss by OAE in Asphyxiated Newborns

1

Elaheh Amini ; Zahra Kasheh Farahani ; Mehdi Rafiee Samani ; Hamed Hamedi ; Ali
1
1
1
1
2,*
Zamani ; Alireza Karimi Yazdi ; Fatemeh Nayeri ; Firoozeh Nili ; Golnaz Rezaeizadeh
1Family Health Institute, Breastfeeding Research Center, Tehran University of Medical Sciences, Tehran, IR Iran
2Family Health Institute, Maternal, Fetal and Neonatal Research Center, Tehran University of Medical Sciences, Tehran, IR Iran

*Corresponding Author: Golnaz Rezaeizadeh, Family Health Institute, Maternal, Fetal and Neonatal Research Center, Tehran University of Medical Sciences, Tehran, IR Iran. Tel: 982166591316, E-mail: golnaz_rezaei80@yahoo.com

Received: June 17, 2012; Revised: July 17, 2013; Accepted: November 12, 2013

Background: Severe birth asphyxia (apgar < 7 at the 5th minute of birth) is recognized as a hearing loss risk factor by the joint committee
on infant hearing (JCIH). About half of the newborns with hearing loss do not indicate any sign and risk factor at birth. Accordingly, the
joint committee recommended performance of hearing screening test in 2000, especially for babies born with risk factors.
Objectives: The aim of this study was to evaluate hearing loss in asphyxiated neonates. Early diagnosis would result in early treatment of
these newborns.
Patients and Methods: We assessed the relationship between asphyxia and hearing impairment in newborns admitted to a referral
hospital, Tehran, Iran within 3 years (2003 - 2006). Hearing problems were diagnosed and followed by otoacoustic emission (OAE) in the
third and fifth days of birth. Asphyxiated neonates with abnormal OAE were referred to an ENT specialist; second OAE and tympanometry
were carried out after 2 weeks. Based on the results, newborns underwent treatment or were discharged.
Results: Of 149 asphyxiated neonates, 80 had mean first minute apgar score of 4.01, and mean 5th minute score was 7.24. Two percent (3/149)
of asphyxiated neonates had abnormal OAEs. No statistical correlation was found between the 5th minute apgar score and abnormal OAE
(P value = 0.391). However, a significant relationship between the mean birth weight and abnormal OAE (P value = 0.0406) was found.
Conclusions: It seems that birth asphyxia is not correlated with hearing loss.
Keywords: Hearing Loss; Otoacoustic Emissions, Spontaneous; Asphyxia

1. Background
Hearing loss is a common anomaly presenting at birth
(1/500 - 1/1000) (1). It is considered that in a representative
sample of 10000 neonates, 30 have congenital hearing
loss, but only 11 have Down syndrome, five Spina Bifida,
and one Phenylketonuria (2). Based on high incidence of
hearing impairment, the joint committee in 2000 recommended performance of hearing screening test, especially for high-risk babies (3, 4). Congenital deafness can arise
from different causes, including in-utero infection with
cytomegalovirus, immaturity, asphyxia, ototoxic drugs,
hyperbilirubinemia, and a variety of genetic causes with
different modes of transmission. Sensorineural hearing
loss (SNHL) in patients with cerebral palsy due to asphyxia has been defined for more than 50 years (5). Adequate
oxygenation and perfusion are essential for inner ear
function (6) and studies showed that neonatal asphyxia
can causes inner ear degeneration, disappearance of the
outer and inner hair cells, and degeneration of the spiral
and vestibular ganglion cells (7).
Children with impaired hearing, present delays in lan-

guage learning and general development (8). This problem can only be prevented by early diagnosis and management. Some methods are available for screening of
hearing: otoacoustic emission (OAE) and auditory brainstem response (ABR) are two methods of choice for determining/detecting hearing impairment, bedsides being
fast, non-invasive, sensitive, and easy to use at neonates,
although ABR is more expensive (9). OAE test is generally
appropriate for screening neonates hearing. Babies who
are diagnosed and rehabilitated sooner, demonstrate
better language and behavioral skills at the age of five
rather than children diagnosed so late (8). Consequently,
exorbitant costs of treatment would be prevented. In this
study, we have assessed the frequency of neonatal hearing impairment in asphyxiated babies at birth up to 3
years by OAE method.

2. Objectives

The aim of this study was to evaluate hearing loss in asphyxiated neonates. Early diagnosis would result in early
treatment of these newborns.

Implication for health policy/practice/research/medical education:

It seems that birth asphyxia is not correlated with hearing loss. At the same time, it is impossible to say that relative importance of different factors and
their interaction are clearly identified. Indeed, given the results of newborns hearing loss screenings in majority of countries, we are no longer in doubt
that hearing screening should be performed for all newborns, especially the ones at risk during the neonatal period.
Copyright 2014, Iranian Red Crescent Medical Journal; Published by Kowsar Corp.;This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Amini E et al.

3. Patients and Methods

Newborn hearing screening by OAE was initiated in
Imam Khomeini hospital (Vali-Asr), Tehran University of
Medical Sciences (TUMS), as a neonatal referral and academic center, (Tehran, Iran) (2003 - 2006). The target population included every asphyxiated newborn with first
minute Apgar score < 5, and/or 5th minute Apgar score <
6. This case-series study was approved as a student thesis
by the research and medical ethics committee of TUMS
to the Helsinki declaration. Some variables of mothers
and babies were collected in questionnaires (maternal
age, education, type of delivery, drug usage, past history,
neonatal weight, gestational age, Apgar scores, hypoxic
delivery, hyperbilirubinemia, infectious disease history,
and meconium staining).
OAE screening was performed by Echo Screen TE machine (Madsen Electronic, Copenhagen, Denmark) that
uses transient-evoked otoacoustic emission. At the end
of the test, the result was shown on the screen as PASS
when there was OAE response (response to the stimulus
at > 35 dBHL (decibels Hearing Level)), and REFER when
there was no response to the stimulus (9). Screening test
was performed between the 3rd and 5th days of birth.
Babies with a normal OAE were discharged, but in cases
with abnormal OAE (uni or bilateral ), after referring to a
pediatric Ear, Nose and Throat (ENT) specialists (specialized in child hearing loss) for diagnosis confirmation
and management, second OAE and tympanometry were
performed after 2 weeks. In cases with liquid or negative
pressure, treatment was recommended, and then OAE
and tympanometry were performed once more. In cases
with abnormal OAE and normal tympanometry, ABR was
performed immediately. If the baby had first abnormal
OAE and second normal OAE, final OAE was performed in
the 3rd month. In cases with hearing loss after determination of threshold, early intervention (hearing aids and
rehabilitation) and audiologic follow up by behavioral
tests were recommended. Data were analyzed by SPSS
statistical package (version 13). P < 0.05 was indicated as
significant.

4. Results

In this study 149 newborns with birth asphyxia were

evaluated for hearing loss. Demographic and clinical
characteristics of the asphyxiated neonates are shown in
Table 1. Of 149 cases, 38 (25.5%) failed the test (13 unilateral,
25 bilateral). Among them, only 22 neonates came for the
2nd OAE, 13 of which had abnormal OAEs (6 unilateral and
9 bilateral), and finally 6 children went through the third
step of screening process, three of which had abnormal
test results. Of 149 asphyxiated neonates, 40 were born
with NVD, 10 (25%) failed the test, and of 109 cases (73.2%)
with C/S, 28 cases (25.7%) failed the test (P value = 0.031).
Of 38 cases who failed the test, 22 were male and 16 were
female, who failed the TEOAE (P value = 0.914).
2

Table 1. General Characteristics of Asphyxiated Neonates

Age, mean SD, week
Sex, No. (%)

35.5 3.36

Female

60 (40)

Male

89 (59)

Weight, mean SD, gr

Apgar (1st min)

Apgar (5th min)

Type of delivery, No. (%)

Total

Number: 149

2363 899
4.01
7.24

C.S

109/73 %

NVD

40/26 %
149/100 %

The highest and lowest gestational ages were reported

40 and 26 weeks, respectively. Newborns with abnormal tests represented mean gestational age of 34.12 3.7
weeks and mean birth weight of 2014.21 344 g compared
with those with normal OAEs with mean gestational age
of 36.05 3.7 weeks and mean birth weight of 2551.35
446 g (P value = 0.0406). Of 149 cases, 80 had first minute
Apgar score of less than 5, 28 of which (35%) failed the test
(mean Apgar score of first minute was 4.01), but among
these neonates only 24 had 5th minute Apgar score of less
than 6 (mean Apgar score = 7.24), and 5 (22.7%) failed the
test. But in 69 cases, first minute and 5th minute Apgar
scores were higher than 5 and 6 respectively, asphyxia
diagnosis based on clinical signs of the first hours of
birth, fetal bradycardia, and meconium stained amniotic
fluid. It is noteworthy that no significant relationship
was found between abnormal OAE and 5th minute Apgar
score of less than 6 (P value = 0.391).

5. Discussion

Hearing loss can be considered as one of the most important birth defects. Birth asphyxia and ischemia have
often been thought to be major causes of early hearing
loss or deafness. Experiments have confirmed/shown that
hypoxia induces the ABR elevation threshold in rat and
cat neonates (10). Several studies have confirmed that the
incidence of hearing loss among babies in NICU with low
Apgar scores in the first and 5th minutes of birth is much
higher than the general population (2 - 4%). They can have
a high rate of middle ear pathology, which would potentially affect their OAEs (11). Early detection of hearing loss
especially in high-risk babies by screening at, or shortly
after birth, and appropriate interventions, are critical to
speech, language and cognitive developments. In addition, Tower in his study emphasized that ABR has to be
done for these babies firstly; after failing this test, OAE
should be the next step (12). However he didnt find any
significant differences between the sample and control
group. He stated that influential high-risk factors such
Iran Red Cres Med J. 2014;16(1):e6812

Amini E et al.
as Asphyxia, hyperbilirubinemia, low birth weight, mechanical ventilation, familial history of hearing loss, and
hospital stay in NICU more than 2 days, should be considered. Each neonate might be evaluated seriously regarding hearing impairment.
Of 149 neonates in our study, approximately 2% (3/149)
had abnormal OAEs, but we may underestimate this rate,
since some of our cases with abnormal OAEs did not continue the follow up. Our finding was more than the incidence of hearing loss at birth (1/500 - 1/1000), however, in
another study the rate of abnormal OAE at high-risk newborns was reported approximately 2% (13). Furthermore,
Ohl and his colleagues in 2009 found that 3 - 5% of atrisk
neonates suffer from hearing loss (8). Another study from
Saudi Arabia reported this rate of prevalence about 1.3%
(14). It seems that in our complicated neonates, large
number of causative factors might be involved affecting
the incidence of hearing loss. In our study, a positive relationship was found between the mean birth weight and
normal OAE. Presumably, abnormal OAE with low mean
birth weight could be due to presence of IUGR and low
birth weight (LBW) babies. Previous studies showed that
the incidence of hearing impairment in premature and
LBW babies is 20 times more than babies with normal
weight. Two percent of newborns with < 1500 g suffered
from hearing loss (15, 16).
Babies who were born by C/S had more abnormal OAE
in comparison with NVD-born babies (P value = 0.031). It
seems that spinal or epidural anesthesia had some effects
on the hearing system (7). In addition, it is noteworthy
that these babies were probably at a higher risk of emergency delivery due to issues such as prematurity, PROM,
and LBW. Olusanya et al. in 2004 reported some significant risk factors for hearing impairment such as young
maternal age, prolonged and obstructed labor, prematurity, and prolonged rupture of membranes. These factors
also have a great role in the type of delivery (14). Twentytwo males (24.7%) and 16 females (26.7%) failed the TEOAE
(P value = 0.914) in our study. Therefore, we could not
see any important difference between the two genders,
although almost all investigations support that hearing
loss is more common in males than females. Male to female ratio of 1.2:1 was reported (17); boys may be at high
risk for hearing loss, since they are more prone to serious
neonatal diseases such as RDS and sepsis (15). One study
mentioned high frequency of unilateral hearing loss in
boys and equally-distributed bilateral hearing loss between males and females (18).
We also found that there is no significant correlation
between congenital hearing loss and exclusively the 5th
mean Apgar score as an important feature for severity of
asphyxia. This finding is compatible with former studies, too (5). However, some studies have pointed out that
asphyxia and low Apgar score are the reasons for temporary hearing loss, not permanent status (19). Moreover, in
another study carried out in Shanghay hospital, Japan,
the effects of prolonged asphyxia during parturition on
Iran Red Cres Med J. 2014;16(1):e6812

auditory brain stem were assessed. They did not find any
tremendous impact of asphyxia on this neural part (20).
Furthermore, Jiang et al. in 2004 reported that after 3
days hypoxic-ischemic damage to central auditory system, it tends toward recovery and after 1 week the system
recovers significantly (20). Another study in 1999 indicated that fetal hypoxia, of any degree and duration, is not a
particular reason for permanent hearing loss (10). Finally,
Bergman in 1984 confirmed that Apgar scores, low PaO2
and high PaCo2 were not independent risk factors for
hearing loss (15). Familial history of hearing loss could be
one major cause of abnormal OAE (2), but we didnt study
this factor in our investigation.
As a matter of fact, evaluation of the exact etiology of
neonatal hearing loss in children with complicated deliveries is difficult because of the large number of causative
factors involved. However, it seems that birth asphyxia is
not correlated with hearing loss; at the same time it is impossible to say that the relative importance of different
factors and their interactions are clearly identified. Indeed, given the results of newborns hearing loss screening in majority of countries, we are no longer in doubt
that hearing screening should be performed for all newborns, especially the ones at risk during neonatal period.

Acknowledgements

There are no acknowledgments.

Authors' Contributions

Elaheh Amini and Ali Zamani: Designed the study. Zahra

Kasheh Farahani: wrote the manuscript. Mehdi Rahimi
Samani and Hamed Hamedi: collected the data. Alireza
Karimi Yazdi: consulted the ENT ward. Fatemeh Nayeri
and Firoozeh Nili: consulted the pediatrics ward. Golnaz
Rezaeizadeh: wrote and edited the manuscript.

Financial Disclosure

There is no financial interest to disclose.

Funding Support

There is no financial support.

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Iran Red Cres Med J. 2014;16(1):e6812