Long-term and short-term variations in amplitude and frequency of spontaneous otoacoustic emissions in pre-term infants.

In pre-term infants, spontaneous otoacoustic emission (SOAE) frequencies show an upward shift with time. The present study aimed to monitor the SOAE amplitude variation during this frequency shift. A long-term observation of 87 SOAE frequencies from 18 pre-term infants yielded a positive frequency shift of 0.72 per cent per week, which was not accompanied by a simultaneous amplitude shift, as the mean variations in SOAE amplitude were practically zero. Furthermore, there was no relationship between the short-term SOAE amplitude variation and the infant's post-conceptional age. Only the absolute amount of SOAE amplitude variation seemed to grow with time. Comparison with induced variations in SOAE frequency argues against a middle ear influence on the SOAE frequency shift. In our view, the absence of any amplitude shift during the upward SOAE frequency shift further suggests cochlear development during the last period of gestation.