Otoacoustic emissions in preterm infants: indications for cochlear development?

A longitudinal study of click-evoked otoacoustic emissions (CEOAEs) in 19 ears of 11 preterm infants--post-conceptional age (PCA): 30 to 39 weeks--resulted in a total of 90 CEOAE recordings. All but one of the 19 ears showed an increase of CEOAE amplitude at increasing PCA. The mean increase rate was 1.36 dB per week (dB/wk) for the left ears (n = 11, SD = 1.04 dB/wk), and 1.17 dB/wk for the right ears (n = 8, SD = 0,87 dB/wk). In six ears of three infants we were able to follow a total of 15 frequencies of spontaneous otoacoustic emissions (SOAEs). All of the monitored SOAE frequencies showed a positive shift in frequency with time, ranging from about 10 Hz/wk around 2000 Hz to about 50 Hz/wk around 5000 Hz. This increase of CEOAE amplitude and SOAE frequency indicates that OAE properties are not fully developed in preterm infants. Although the influence of middle ear properties cannot be excluded or proved, the observed SOAE frequency shift suggests development of the fine structures in the cochlea itself.