Neonatal auditory brainstem response thresholds to air- and bone-conducted clicks: 0 to 96 hours postpartum.

Auditory brainstem response (ABR) thresholds to air- and bone-conducted clicks were investigated in 40 full-term neonates. Subjects were divided into two groups of 20 according to postpartum age: less than 48 hours and between 49 and 96 hours. Mean ABR thresholds to air- and bone-conducted clicks for neonates less than 48 hours postpartum were 14.5 dB nHL (51.5 dB peak SPL) and 1.8 dB nHL (36.8 peak re: 1 microN), respectively, while those for neonates between 49 and 96 hours were 3.8 dB nHL (40.8 dB peak SPL) and 1.5 dB nHL (36.5 dB peak re: 1 microN), respectively. A significant difference was found between the two group mean ABR thresholds to air-conducted stimuli (p < .0001) but not for the bone-conducted stimuli (p < .8959). A statistically significant within-group difference was found between the ABR thresholds to air- and bone-conducted stimuli for only the neonates less than 48 hours of age (p < .0001). When the data was collapsed across groups, simple linear regression analyses revealed a statistically significant relation between postpartum age and ABR threshold to air-conducted stimuli (p < .0001) and a nonsignificant relation between postpartum age and ABR threshold to bone-conducted stimuli (p < .9744). These findings support the notion that some resolution of fluids and residuals in the middle ear occurs during the first 48 hours postpartum and that air-conducted stimuli are attenuated during that period. As such, a physiologic conductive deficit among the younger neonates is suggested.