Functional integrity of rostral regions of the immature brainstem is impaired in babies born extremely preterm

•The most important abnormality in brainstem evoked response in babies born at 23-27 weeks of gestation was a significant increase in III-V interval and its click rate-dependent change.•Babies born extremely preterm have a major impairment in functional integrity in the rostral regions of the immature brainstem.•The impairment in extremely preterm babies is more significant than in late and very preterm babies.

ObjectiveBabies born extremely preterm are predisposed to brain damage. We test the hypothesis that functional integrity of the auditory brainstem, particularly the rostral regions, is impaired in extremely preterm babies.MethodsWe recruited 68 babies who were born at 23-27 weeks of gestation. At term date, these babies were studied by recording and analysing maximum length sequence brainstem auditory evoked response (MLS BAER) with click rates 91-910/s. Detailed data analysis was performed in 65 babies from whom reliable MLS BAER measurements were obtained.ResultsCompared with normal term controls, the extremely preterm babies showed a significant increase in wave V latency, and I-V interval at all rates 91-910/s (p < 0.01-0.001). Of two small intervals, I-III interval showed no apparent abnormality, but III-V interval was significantly increased at all rates, which was supported by a significant increase in III-V/I-III interval ratio (all p < 0.001). These abnormalities were more significant at higher than at lower rates. The slopes of wave V latency-, I-V interval- and particularly III-V interval-rate functions were all increased. The same was true for the slope of III-V/I-III interval ratio-rate function.ConclusionsMLS BAER variables that mainly reflect central neural conduction in the extremely preterm babies were abnormally increased. The most important abnormality was a significant increase in III-V interval and its click rate-dependent change. The abnormalities tended to be more significant than those previously reported in late and very preterm babies.SignificanceBabies born extremely preterm have a major impairment or maturational delay in functional integrity of the rostral regions of the immature brainstem, which is more significant than in less preterm babies.