Newborn Hearing Screening: OAE, ABR, Risk

The auditory system begins developing early in embryonic life, with the cochlea reaching structural maturity by approximately 20 weeks of gestation and functional maturity by 28-30 weeks. By the third trimester, the fetus can respond to sound, demonstrating heart rate changes and motor responses to auditory stimuli. At birth, the peripheral auditory system (outer ear, middle ear, cochlea, and auditory nerve) is structurally mature, although the central auditory pathways (brainstem to auditory cortex) continue to mature throughout the first two years of life, driven by auditory stimulation. Sound travels through the external auditory canal to the tympanic membrane, which vibrates in response to pressure waves. These vibrations are transmitted through the middle ear ossicles (malleus, incus, stapes) to the oval window of the cochlea. Within the cochlea, fluid waves displace the basilar membrane, which activates the inner hair cells (approximately 3,500 cells arranged in a single row). Inner hair cells are the primary sensory receptors that convert mechanical energy into electrical signals transmitted via the cochlear nerve (CN VIII) to the brainstem. The outer hair cells (approximately 12,000 cells in...