ABSTRACT The normal development of auditory neurons is critical for the processing and interpretation of sound, which is essential for language development, social interaction, and overall cognitive function. A lack of adequate oxygen supply during fetal development can damage these neurons, resulting in long-term consequences. Intrauterine hypoxia refers to oxygen deficiency in the womb. Reduction of intrauterine oxygen supply to the developing fetus, primarily produced by chronic placental insufficiency, results in intrauterine growth restriction (IUGR) — a common complication of pregnancy and significant prenatal problem in preterm infants. IUGR significantly affects brain maturation, resulting in neurological impairment and developmental deficits. For decades, a large number of investigators have studied the impact of IUGR on the functional integrity of auditory neurons along the brainstem auditory pathway in preterm infants. By using brainstem auditory evoked responses, many investigators found some auditory abnormalities, whereas others did not. The diversity of findings makes it difficult to reach a consensus regarding the impact of IUGR on the developing auditory brainstem. A relatively new technique, called maximum length sequence brainstem auditory responses, has recently been used to study brainstem auditory function in infants to improve the understanding of neurophysiology underlying brainstem auditory abnormality and enhance the detection of auditory abnormality. Recent studies have shown that intrauterine hypoxia associated with IUGR adversely affects the early development of the brainstem auditory system in preterm infants, resulting in brainstem auditory abnormalities that vary with different gestations. This article reviews up-to-date findings in the functional integrity of the brainstem auditory pathway in preterm infants born of IUGR. Particular attention is paid to the findings obtained at term equivalent age in late and very preterm infants to provide valuable insight into the impact of intrauterine hypoxia on the auditory system in infants born at different gestations. Overall, the recent findings contribute to a better understanding of the impact of intrauterine hypoxia associated with IUGR on the developing auditory system, underscore the need for continued investigation in this area, and highlight the importance of early detection and intervention of auditory abnormality for preterm IUGR infants, especially those born very preterm, to prevent long-term auditory disorders.
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