Brainstem auditory pathway function at four months of corrected postnatal age in preterm infants born below 30 week gestation.

Objective: Functional status of the brainstem auditory pathway was examined at four months of corrected postnatal age in infants born below 30 week gestation to assess the effect of very or extremely preterm birth on postnatal development of the pathway.

Methods: Thirty-four preterm infants born at 24-29 week gestation (GA24-29w) were studied at four months of corrected postnatal age. Normal controls were 38 postnatal age-matched term infants. Maximum length sequence brainstem auditory evoked response (MLS BAER) were recorded and analysed with 60 dB nHL clicks.

Results: Compared with term control group, GA24-29w group manifested higher BAER threshold (p < 0.05), longer MLS BAER wave latencies at all click rates 91-910/s (p < 0.01-0.001), and lower wave amplitudes at most click rates (p < 0.05-0.01). No significant differences were found between the two groups in I-V interval at any click rates. I-III interval was shorter while III-V interval was longer in GA24-29w group than in term group at higher rates (all p < 0.05). III-V/I-III interval ratio in GA24-29w group was greater at 455 and 910/s clicks (p < 0.05 and 0.01). These interval variables showed similar changes when 4 GA24-29w infants with threshold elevation were excluded.

Conclusions: At four months of corrected postnatal age, infants born below 30 week gestation manifested elevated BAER threshold, increased wave latencies, and reduced amplitude. They also manifested a small decrease in I-III interval but a small increase in III-V interval at high rates. Very or extremely preterm birth exerts a mild or moderate effect on postnatal development of the brainstem auditory pathway.