Screening for auditory dysfunction in high risk neonates

Abstract

Brainstem auditory evoked responses were recorded in 117 pre-term and 71 full-term infants from the general population of infants born at a referral obstetric unit. The threshold intensity required to evoke a reliable BAER was determined at different post-menstrual ages (PMAs) and in many cases at follow-up clinics. The BAER thresholds for 12 infants born and tested at less than 31 wk PMA were all ⩾ 50 dBHL. Sixty-two low-gestational-age infants who were tested between 31 and 36 wk PMA had BAER thresholds between ≤30 dBHL and ⩾ 80 dBHL. The majority of pre-term and term infants tested at term equivalent age had BAER thresholds ≤ 30 dBHL. Longitudinal studies also indicated that BAER thresholds can decline rapidly during the pre-term period. Follow-up studies showed that those pre-term and term infants with BAER thresholds ≤ 30 dBHL had normal auditory thresholds as determined using conventional behavioural testing at 4 or more months of age. Of those infants with BAER thresholds ⩾ 40 dBHL at the time of discharge or at term equivalent age, 67% ( n = 16) were confirmed later as having a moderate to profound hearing deficit. The remaining 8 infants in this group had had BAER thresholds at term of 40 or 50 dBHL and had normal BAER and behavioural thresholds at follow-up. The cross-sectional and longitudinal data indicate that the majority of low-gestational-age infants who are at risk of hearing deficit achieve BAER thresholds ⩽ 30 dBHL by term equivalent age. We recommend that auditory screening of infants in this group is best performed at the time of discharge from hospital or at term equivalent age, whichever is the later. Those infants with thresholds ⩾ 40 dBHL at that time should be encouraged to attend follow-up testing and, if high thresholds persist, they should then be referred on for behavioural testing and assessment for habilitative support.