The study was carried out in the form of targeted hearing screening program restricted to a study group of 200 neonates incubated in NICU in the time period between March 2020 and January 2021 and were subjected to risk factors for hearing loss. The most common risk factor in the study was prematurity; total premature neonates were 164 (82%). Prematurity alone as only risk factor was 25% while combined with low birth weight was 57% in 114 neonates. Our finding is in accordance with other literature in which prematurity was the most common risk factors among neonates in NICU [15]. On the other hand, our result did not match with other studies in which other risk factors were the major one like severe birth asphyxia and hyperbilirubinemia [16] and ototoxic medications [17]. The difference between the studies in the common risk factors may be due to the variability in environmental conditions surrounding the pregnancy or birth and the difference of medical care between the hospitals.
The probability of hearing loss increases with an increase in the number of risk factors [17]. In our study, there is statically significant effect of the combination of preterm and low birth weight on hearing loss (p < 0.006). HL is a severe consequence of prematurity; its prevalence is inversely related to the maturity of the baby. Premature infants have many concomitant risk factors which influence the occurrence of hearing deficit [18]. On another hand, the risk factors for hearing loss in Ohl et al. study were neurological disorders, asphyxia, family history of hearing loss, and TORCH (toxoplasmosis, other agents, rubella, cytomegalovirus, herpes simplex) infection, but hearing loss was not associated with low birth weight or birth before 34 weeks of gestation which is different from our results [19].
In the present study, based on the diagnostic ABR results, the percentage of hearing loss is 1% (2 cases). The prevalence of hearing loss among neonates in NICU is variable in different studies. Some studies reported prevalence close to our results 1.6 % [20], 1.7 % [21], and 0.8 to 2.0 % [22], while others reported higher prevalence 5.09 % [23], 4,3 % [24], 4.55 % [19], and 4.91% [25]. The difference in the prevalence of hearing loss might be related to several factors like differences in screening and diagnostic methods of hearing loss [23]; Hl may be affected by indirect medical factors as the availability and quality of healthcare provisions including birth clinics, NICU, and vaccination programs.
The risk factors for the development of ANSD have been studied in different literatures, and associations have been gathered. Some of the risk factors that have been identified are intracranial hemorrhage, asphyxia, hyperbilirubinemia, prematurity, low birth weight, neonatal ventilation, ototoxic drug exposure, dysmorphic features, Apgar scores, respiratory distress, cytomegalovirus infection, sepsis, meningitis, asphyxia, and family history of hearing loss [26,27,28,29,30]. In the current study, seven neonates (3.5%) had hyperbilirubinemia with levels exceeded 20 mg/dl, and all had blood exchange within 24 h. The four out of seven who completed the diagnostic test had normal hearing.
Possible explanation that neonates with hyperbilirubinemia in the current study had no auditory neuropathy is the early blood transfusion. These neonates were subjected to blood transfusion early which helped to rapidly decrease the level of the bilirubin in the blood before the affection of the auditory nerve and decrease the possibility of auditory neuropathy spectrum disorder (ANSD) to occur. This agrees with a screening study conducted by Xu et al. (2019) on a group of neonates who met the standard of exchange transfusion and another group of neonates in the same period who did not require exchange transfusion. They found lower incidence of auditory neuropathy in the exchange transfusion group than in the phototherapy group. They also noted that plasma exchange can rapidly reduce serum UB level to 40–60% of the original level, and when it is combined with blue light phototherapy, the UB level can be decreased to 60–80% of original level 24 h later [31]. So, more attention should be paid on the effective role of blood transfusion in the prevention of auditory neuropathy in the future.
Another point to be mentioned in the current study is the pass rate of the TEOAE frequencies included in the screening program. There was a statistically significant difference between the pass rate of frequencies in the same ear (p < 0.001); the highest pass rate was on 4 KH (91%) followed by 3 KH (85%), and the least pass rate was on 1 KH (11.5%). This difference of the pass rate between the frequencies is reported in other screening programs in which higher frequencies (e.g., 2–4 or 2–5 kHz) had lower referral rates than lower frequencies (1–4 kHz) [32]. The stiffness of middle ear increases due to reducing the middle-ear air space by the presence of amniotic fluid and mesenchyme in the middle ear which occurs in early newborn life and therefore affects the transmission of lower-frequency sounds which can be associated with greater referral rates [33]. So, the use of higher frequencies TEOAE instead of lower frequencies will be valuable to ensure better result of newborn hearing screening.
