Hearing improvement in preterm infants with sensorineural hearing loss

Aims The aim of this study was to assess the prevalence of hearing recovery over months in preterm infants with a confirmed diagnosis of sensorineural hearing loss (HL), and evaluate which perinatal and postnatal factors might influence hearing improvement. Population The present study included all preterm infants who had bilaterally failed universal newborn hearing screening, and received diagnostic confirmation of sensorineural HL (T0) by click-evoked auditory brainstem responses (ABRs) performed within the first 3 months of life in our tertiary level referral audiologic center in Milan (Italy). Methods The hearing threshold was reassessed at 18 months corrected age (T1) by click-evoked ABRs. Clicks were presented at a rate of 21.1/sec with a maximum stimulation level of 105 dB nHL. The prevalence of hearing recovery and associations between possible risk factors (Gestational Age/Birth Weight ratio, type of delivery, low APGAR score, jaundice requiring phototherapy, use of ototoxic drugs for more than 5 days, sepsis, respiratory distress syndrome, anemia, retinopathy of prematurity, intraventricular hemorrhage, and type of infant feeding for at least 3 months after discharge from the hospital) and hearing changes were evaluated. Results A total of 138 patients met the inclusion criteria. The mean gestational age was 30 weeks and 2 days (ranging from 162 to 255 days), and the mean birth weight was 1345 grams (440-2850 grams). Complete recovery of the hearing threshold was observed in 35.5% of the study subjects (49 out of 138). The highest percentage of complete hearing recovery at T1 was found for infants affected by mild HL (87.0%, 20/23), followed by infants with moderate (44.7%, 17/38), severe (29.2%, 7/24) and profound (9.4%, 5/53) HL. Overall, the percentage of hearing improvement (>10 dB nHL) was 58.7% (81/138). Multivariate analysis confirmed a higher prevalence of hearing improvement among preterm infants who had received exclusive breastfeeding or mixed feeding compared with those who had received exclusive infant formula (80% versus 29.3%, adjusted RR: 0.41, 95% CI: 0.26-0.63, p<0.001). Interpretation The present study demonstrates that an improved hearing threshold is expected in a high percentage of preterm infants diagnosed with sensorineural HL, confirming the importance of performing a long audiological follow-up and the need to postpone the indication for cochlear implantation. Breast milk might play a protective role on the auditory system of preterm infants, probably due to the high expression of mesenchymal stem cells and total antioxidant capacity. Conclusion These findings could have important implications for clinical practice, suggesting a possible positive impact of breast milk on the long-term hearing outcomes of preterm infants.