Plessinger M A, Woods J R
A.E. Seeds Perinatal Research Center, University of Cincinnati, Ohio.
Am J Obstet Gynecol. 1987 Dec;157(6):1382-7. doi: 10.1016/s0002-9378(87)80228-4.
The fetal auditory brain stem response to increasing stimulus rates of 16, 32, 45, 64, 87, and 100 clicks/sec were determined in eight fetal lambs of 115 to 136 days' gestation (term = 145 days). To conduct these studies, a hysterotomy was performed on the pregnant ewe at 110 to 118 days' gestation to implant stainless steel electrodes in the fetal scalp and a hearing aid receiver in the fetal external ear canal. The fetus was returned to the uterus and the pregnancy was allowed to continue. Auditory brain stem responses from younger fetuses (115 to 125 days' gestation) were present at the slower click rates but were not observed consistently at the fast click rates until the fetuses were older (125 to 136 day's gestation). Latency values of the auditory brain stem response peaks decreased with increasing fetal age and increased with increasing stimulus rates. From a two-way analysis of variance, the influence of age and click rate alone and more important, the interaction of age and click rate were determined to have highly significant effects (p less than 0.001) on latency values of wave 1, wave V, and central conduction time. These auditory brain stem response results suggest that the cochlear component of the fetal auditory system undergoes rapid change in late gestation to process incoming stimuli at a faster rate.
