Neonatal screening for hearing loss and its risk factors at a tertiary hospital; A : Prospective Cross sectional study.

Introduction

Detecting and rehabilitating neonates with hearing impairment is a healthcare priority. In developed nations legislation exists to enforce rehabilitation latest by 6 months of age.¹ Delay in intervention beyond 6 months results in low educational and employment levels in adulthood.^2,3 Every year in India an estimated 1,50,000 newborns are born with hearing impairment. A majority of these are rehabilitated as late as 5 yr of age.⁴ The American Academy of Pediatrics Task Force on Newborn and Infant Hearing stated, "significant bilateral hearing loss has been shown to be present in approximately 1 to 3 per 1000 newborns in the well-baby nursery population, and in approximately 2 to 4 per 1000 infants in the intensive care unit population".⁵ In a study done in South India, out of every 1000 children born in India, there may be 5–6 such children who cannot hear properly.⁶ Hearing loss is one of the most common congenital anomalies, occurring in approximately 2-4 infants per 1000. The ability to hear during the early years of life is critical for the development of speech, language, and cognition. Because there are no visual indicators, most hearing-impaired children who are not screened at birth are not identified until between 1½ and 3 years of age, which is well beyond the critical period for healthy speech and language development. Auditory brainstem response, auditory steady state response, and otoacoustic emission testing provide critical information about the status of the auditory pathways, however they are not direct measures of hearing.⁷ Only behavioral testing can provide a direct measure of hearing.⁸ When carefully performed, using appropriate criteria (including changes in sucking as an indication of a response), behavioral observation audiometry can accurately measure thresholds in infants younger than 6 months.⁹ The All India Institute of Speech and Hearing (AIISH), conducts infant screening for hearing disorder on regular basis in different hospitals attached to it using Behavioral Observational Audiometry (BOA), Otoacoustic Emissions (OAE) screening, and administering High Risk Register . In the year 2009–2010, a total of 12416 newborns in 10 hospitals associated with AIISH were screened for hearing disorder. Of them, 1010 infants were referred for further checkup.¹⁰

However, with the help of newborn hearing screening, a hearing-impaired child can be identified and treated early. In such a case, the child will most likely develop language, speech, and social skills comparable to his or her normal-hearing peers, and thus avoid a lifetime of hearing-loss related disabilities. Though Auditory brainstem response is the gold standard for certifying neonatal hearing loss, it is time consuming procedure, hence it is difficult to perform on all children. Behavioral observation audiometry is a dependable screening tool for the same. Hence it is necessary to screen all neonates for hearing impairment. Hearing loss and deafness are universal problems that affect at least 278 million people worldwide. More than 60% of these people live in developing countries¹¹. The prevalence of hearing impairment among general population ranges from 0.09 to 2.3%^12,13. The following risk factors have been listed to identify newborns with high risk criteria for developing hearing loss by various studies. These include family history of congenital or delayed onset childhood, sensorineural hearing loss, maternal infection TORCH group, congenital anomalies (craniofacial abnormalities), low birth weight, hyperbilirubinemia, prematurity, use of ototoxic drugs, NICU admission, birth asphyxia and neonatal seizures. Prevalence of neonatal hearing loss in the high risk population ranges from 0.3 to 14.1%^14,15.

Nonbehavioral tests like ABR testing, ASSR testing, and OAEs are used commonly in estimating peripheral hearing in infants. However only behavioral tests permit measurement of what an infant actually perceives, hence they are measures of functional hearing abilities.⁷

Early identification of hearing screening at birth and fitting hearing aids early is suggested for effective rehabilitation in various studies. Apuzzo¹⁶ and Yoshinaga-Itana et al¹⁷ in their studies have demonstrated that infants who are fit with appropriate technology before they are 6 months old can develop speech and language skills on par with their normal hearing peers, and that infants fit with technology older than 6 months, do not catch up to those fit earlier. Sharma et al¹⁸ have also demonstrated that infants who receive auditory stimulation at a sufficiently early age have evoked potential latencies similar to normal hearing peers, however infants who do not receive auditory stimuli early do not develop. With the above considerations we decided to conduct a study with the objective of screening neonates for hearing impairment using behavioral observation audiometry.

Material and Methods

Type of study: Prospective Cross sectional study

Study setting: Neonates born at at ESIC-MC & PGIMSR, Bangalore. This is a tertiary hospital which caters health needs of insured persons.

Study population: Neonate, any newborn who is born at ESIC-MC&PGIMSR, who is willing to participate.

Sample size: Relying on prevalence of newborn nearing impairment as mentioned by Nagapoornima et al6,to be 0.5% with 95% confidence level and a absolute precision of 1%, using Epi info software, a sample size of 146 was calculated. However, to account for factors like non-co-operation and incompleteness of data recording, a total of 160 neonates was studied.

Study duration: 2 months

A questionnaire comprising of detailed sociodemographic profile of mothers of neonates and patients like age, gender, educational status, occupation, income, was designed. A brief history on risk factors for neonatal hearing loss consisting of family history of congenital or delayed onset childhood, sensorineural hearing loss, maternal infection TORCH group, congenital anomalies (craniofacial abnormalities), low birth weight, hyperbilirubinemia, prematurity, use of ototoxic drugs, NICU admission, birth asphyxia and neonatal seizures was recorded.

All 160 selected neonates underwent behavioural observational audiometry. Standard protocol19 for conducting BOA was followed as below

1. Infant was brought into test room which is silent in hungry state.

2. Seat infant so torso is supported and infant is not fidgety, and so tester(s) can easily see mouth.

3. Monitor infant state during testing and stop if infant becomes fidgety.

4. Instruct parents not to respond to test stimuli or responses from the child.

5. Test assistant will keep infant centered, observe responses, and monitor parents’ behavior.

6. Begin testing in soundfield.

7. Begin testing with a stimulus that is slightly above estimated threshold.

8. Test one low (500 Hz) and one high (2000 Hz) frequency initially and select additional frequencies to test depending on initial responses.

9. Reduce thresholds in 10-dB steps and increase in 5- to 10-dB steps to bracket threshold. Record a response after three reversals.

10. Take breaks as needed to calm the infant and increase usable test time.

11. If sound field testing indicates a hearing loss, test bone conduction.

When neonates failed to respond for stimuli they were considered as screen positive for hearing loss.

Quality control

Pilot testing: Study tool was validated on 5% sample and suitable changes was made to the final proforma .

Ethical consideration: Proposal was submitted to Institutional ethical committee for approval and data was collected after ethical committee approval.

The aim of the study was explained to all mothers of neonates and a written informed consent was taken before the interview. Informed consent and thumb impression was taken from the mothers who cannot read or write. Subjects were assured of complete and strict confidentiality of the information collected.

Checklist for parents to monitor auditory and language milestones up to 6 months:

Parents were educated to look for the following milestones till 6 months of age and report immediately if these were not attained. The auditory milestones were: startling or turning head to a loud sound and child getting aroused from light sleep by an “sshhh” sound. The language milestones like: producing differential cries to hunger and happiness, repeating the same sounds (cooing/ gooing). The checklist was printed and given to the parent. In case of any delay in the milestone the parents were asked to come for follow up.

Results

1) Age and gender distribution on the neonate screened:

Totally 160 neonates were studied of which 53.1% were boys and 46.9% were boys as shown in table1. Mean age of the neonate screened was 5.45 ±3.22 days, youngest child was one day and oldest child being 23 day old.

2) Socio demographic profile of mothers of the neonate screened:

Table 2 shows Sociodemographic details of mothers of neonates. Most of the mothers were between the age group of 26 years to 30 years. More than half of the mothers were homemakers. 40.6% of mothers had their education upto high school, 27% of mothers had some degree education however 5.6% of the mothers stated they were illiterates. All mothers are either workers or wife of workers who are covered by ESI scheme.

3) Screening for hearing impairment:

Table 3 shows results of Hearing impairment screening among neonates using Behavioral Observation Audiometry. Of all the neonates screened 4 (2.5%)of them had hearing impairment of which three were girls and one boy.

4) Risk factors for hearing impairment among neonates:

Table 4 shows the Risk factors for hearing loss in the neonates. 27.5% of the neonates were born preterm being the most common risk factor followed by hyperbilirubinaemia (21.9%), low birth weight (13.13%), NICU admissions (9.4%) and vaginal discharge in mothers during antenatal period being 6.9%. It was fortunate to observe that all mothers had adequate antenatal check ups, none of the mothers had consumed and ototoxic medications.

Discussion:

The prevalence of hearing impairment on screening with BOA was found to be 2.5% after confirmation with ABER if was found to be 0.64%. The prevalence of hearing loss among healthy newborns if found between 0.5-6% across the world in various studies^20–25. Our prevalence is comparable with that of other studies.

Behavioral testing though picks false positives, it allows the parents to participate in testing. Following testing as parents are provided with information about what to observe, they can be active participants in testing, facilitating acceptance, and understanding of hearing loss²⁶. Although ABER and OAE testing provides important information about the status of the auditory system, only behavioral testing directly tests hearing. Hence, it is critical that audiologists have to use behavioral technique that is accurate for assessing hearing in infants younger than 6 months²⁷. However limitation of using behavioural observation audiometry that in developmentally retarded children in whom responses are difficult to elicited, this test is not so conclusive.

Many countries have mandated newborn hearing screening requirements as the prevalence of newborn hearing impairment is increasing and early intervention is found to be beneficial. As more infants survive and as hearing screening becomes more universal, audiologists are being asked to assess hearing in very young infants who have failed newborn screening and to manage hearing loss when it is identified. One of the first steps in hearing loss management is the selection and fitting of appropriate amplification. Hearing aid fitting requires an accurate assessment of the degree and type of hearing loss, with both ear and frequency specific information obtained by air and bone conduction.

Risk factors for hearing impairment are more prevalent in our study. 27.5% of the neonates were born preterm being the most common risk factor followed by hyperbilirubinaemia (21.9%), low birth weight (13.13%), NICU admissions (9.4%) and vaginal discharge in mothers during antenatal period being 6.9%. Studies which evaluated neonates in neonatal intensive care units found prevalence rates of hearing impairment ranging from 3 to 14.1%²⁸. Other studies have reported hearing impairment prevalence from 1-17%²⁸. In a study done by Vashista et al has found that, prematurity and low birth weight to be associated with hearing loss is 17.02 and 17.05 %²⁹. Vohr et al has found that impaired hearing reaches up to 17 % in very low birth weight neonates and In infants having a NICU stay of 5 days hearing loss was up to 20.68 %³⁰.

Hearing loss is one of the commonest childhood disabilities with a huge burden in developing countries like India. Its an urgent need to address this issue. There are no programs for active detection of hearing impairment among children and poor reactions of a child to acoustic stimuli are ignored confusing to some underlying ear diseases. Hence early detection by screening is the only feasible and has been a long-standing priority.

Conclusion

The study was aimed to detect the prevalence of hearing impairment in new born infants, and the prevalence was found to be 2.5%. Prevalence of hearing impairment among girls was found to be higher compared to that of the boys. Risk factors for hearing impairment like pre term birth, low birth weight, hyperbilirubinaemia was found to be high in the study population such neonates need to be followed up at 3 months for delayed onset or progressive neonatal or postnatal hearing loss. Early diagnosis and intervention is the key for development of speech, hence there is a need for neonatal hearing screening program in all the hospitals where delivery services are available.

Early identification of hearing loss offers children the opportunity to develop significantly improved language skills compared with those children who are diagnosed later. Thus neonatal screening can identify such children at an earlier stage which helps in early rehabilitation.