Temporary threshold shifts induced by low-pass and high-pass filtered noises in fetal sheep in utero.

Auditory brainstem responses (ABRs) were obtained from nine late gestational age fetal sheep in utero before and after a 16-h exposure to low-pass (cut-off frequency 1.0 kHz) and high-pass (cut-off frequency 1.0 kHz) noises (approximately 120 dB sound pressure level, recorded in air). Bone-conduction ABRs were elicited by broadband clicks and 0.5, 1.0 and 2.0 kHz tone bursts. Following low-pass noise exposure, ABR thresholds and wave IV latencies increased significantly for 0.5 and 1.0 kHz tone bursts. The high-pass noise exposure produced significant shifts in ABR thresholds and wave IV latencies only for the 1.0 kHz tone bursts. These findings confirm previous reports of low-frequency sound transmission into the fetal inner ear.