Hearing assessment

Audiologists at CHBAH conducted the hearing assessments on all cases and controls. Within 21 days of birth, infants received hearing screening by automated auditory brainstem response (AABR [Maico MB11 BERAphone^®, MAICO Diagnostics GmbH]), with integrated electrodes at an intensity of 35dBnHL. At age six and 12 months, screening included ipsilateral acoustic reflex thresholds, distortion product otoacoustic emissions (DPOAE) and AABR screening. A hearing screening ‘pass’ during the neonatal period included pass AABR bilaterally. A hearing screening ‘pass’ at six and 12 months included either: 1) pass AABR bilaterally, or 2) acoustic reflexes present in at least two frequencies in both ears and three screening DPOAEs present at three frequencies in both ears. Diagnostic hearing assessments for children not passing hearing screening (classified as “referred” hearing screening) included otoscopy, tympanometry, electrophysiological measures (i.e. diagnostic auditory brainstem responses, auditory steady state responses, cochlear microphonic testing), and diagnostic otoacoustic emissions (OAE) and behavioral audiometric evaluations as developmentally appropriate. Audiological management and referral to the pediatric ear nose and throat specialists took place when indicated. SNHL was defined as unilateral SNHL with thresholds greater than or equal to 25 decibels hearing level (dBHL) or bilateral SNHL with thresholds greater than or equal to 25 dBHL in the better ear. Severity of hearing loss was categorized as: mild (26 to 40 dBHL), moderate (>41–55dBHL), moderately severe (56-70dBHL), severe (71–90dBHL), or profound (>90dBHL) [19].