THE EFFECTS OF EARLY AND LATE PRETERM BIRTH ON BRAIN-STEM AND MIDDLE-LATENCY AUDITORY-EVOKED RESPONSES IN CHILDREN WITH NORMAL NEURODEVELOPMENT

In preterm and term infants, brainstem and middle latency auditory evo ked responses (ABR and MLR) were obtained at 40 and 52 weeks conceptio nal age (CA) and at 5 years of age. A neurological and neuropsychologi cal evaluation was performed at 5 years of age. To study the effect of preterm birth on the maturation of the ABR and MLR, the preterm infan ts were divided into early and late preterm groups. Only children with a normal neurodevelopmental outcome at 5 years of age were entered in to the study. For ABR, the late preterm group showed significantly lon ger mean latencies IIc, III, V, and Vc when compared with the term gro up at 52 weeks CA. There was a trend to longer ABR latencies I in the early preterm group compared with the term group. At 52 weeks CA, the late preterm group showed longer mean interpeak latencies III-I and V- I when compared with the term as well as the early preterm group. At 5 years, the late preterm group showed significantly longer mean ABR la tencies IIc and III when compared to the early preterm group. For MLR, the early preterm group showed significantly longer mean latencies of MLR component PO when compared with the term group at 40 weeks CA. At 52 weeks, the late preterm group also had longer mean MLR latencies P O than the term group. At 5 years of age, the term group showed higher mean peak-to-peak amplitudes Na-PO than the early as well as the late preterm group. To a large extent, the ABR results support the hypothe sis that middle ear effusions in combination with retarded myelination of the central auditory pathway are responsible for the ABR differenc es found between term and preterm infants with a normal neurodevelopme ntal outcome at 5 years of age. The longer latencies and interpeak lat encies found in late preterm infants when compared with early preterm infants might be explained by an augmented vulnerability of the audito ry pathway between 30 and 34 weeks CA. The MLR differences found betwe en term and preterm infants might be explained by a difference in the maturation of primary and nonprimary MLR components.