Morphological changes in serial auditory brain stem responses in 24 to 32 weeks' gestational age infants during the first week of life

Objective: The purpose of this investigation was to describe and quantify the sequential morphological changes in the auditory brain stem response (ABR) during the first postnatal week of life in very premature infants less than or equal to 32 wk gestational age. These normative data could be useful in predicting neurological outcome in infants with perinatal risk factors. Design: Sequential ABRs were recorded on a total of 135 infants on 5 out of the first 7 days of life. For analysis, data were grouped by gestational age in 2 wk intervals. In addition, a unique system was devised to categorize waveform response types in premature infants: type 1, a response with normal morphology and replicable waves III and V; type 2, a replicable response with either a wave III or wave V; type 3, a replicable response with neither a wave III or wave V; type 4, a response with no replicable waveform. Results: The frequency of detection of waves improves over the first week of life with the detectability of waves III and V being more frequent than wave I at all gestational ages. There was a gradual improvement in response types in infants > 26 wk with the greatest improvement occurring during the 28 to 29 wk gestation. ABRs were predominantly types 3 and 4 at 24 to 25 wk, type 3 at 26 to 27 wk, type 2 at 28 to 29 wk, and types 1 and 2 at 30 to 31 wk. Absolute wave latencies and interwave latencies also progressively decreased during the first postnatal week. In some infants there was a transient increase in latencies or worsening of response type on the second to third test day. Conclusions: There is progressive improvement in frequency of detection of waves I, III, and V with increasing gestational age. Response types gradually mature over the first postnatal week, particularly in premature infants 28 to 32 wk gestational age.