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 t he sequential morphological changes in the auditory brain stem response (AB R) during the first postnatal week of life in very premature infants less t han 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 a ge in 2 wk intervals. In addition, a unique system was devised to categoriz e waveform response types in premature infants: type 1, a response with nor mal morphology and replicable waves III and V; type 2, a replicable respons e with either a wave III or wave V; type 3, a replicable response with neit her 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 o f life with the detectability of waves III and V being more frequent than w ave 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 w k, 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 tran sient 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 gradual ly mature over the first postnatal week, particularly in premature infants 28 to 32 wk gestational age.