Auditory brainstem responses and behavioural responses in pre-term infants

Auditory brainstem responses (ABRs) and behavioural thresholds were studied in 25 pre-term infants with post-conceptional ages of approximately 40 weeks to ascertain whether there were differences in the ABR between normal preterm and full-term new born infants to compare behavioural thresholds around 40 weeks of post-conceptional age and to follow changes of their behavioural thresholds in the first year of life. ABR thresholds, peak latencies of Waves I and V and the I-V peak interwave latency were measured. Behavioural audiometric thresholds to pure tones were determined through behavioural observation audiometry and conditioned orientation-reflex audiometry. The ABR thresholds of the pre-term infants, whether they were small for date (SFD) or appropriate for date (AFD), were in the normal ranges of the controls. Moreover, there were no significant differences between either the SFD or the AFD group and controls, as far as Wave I or V latency or I-V interval are concerned. Thus, the ABR was apparently unaffected by the infant being small-for dates. Behavioural audiometry disclosed that all normal full-term infants responded to pure tone stimuli, with mean thresholds of 85 dB, while only 42% of AFD and 30% of SFD would respond to pure tone stimuli at 90 dB or less. Behavioural thresholds caught up with the normal range by 12 months of age, except for a few infants.