To examine postnatal functional status of the brainstem auditory pathway in late preterm infants and detect any postnatal auditory abnormality.

Thirty preterm infants born at 33–36 weeks gestation were studied three months after term. None had major perinatal and postnatal complications to minimize confounding effects. Brainstem auditory evoked responses were recorded with 21–91/s clicks.

Compared with postnatal age-matched normal term infants, the late preterm infants did not manifest any major abnormalities in brainstem auditory evoked responses at conventionally used 21/s clicks. At higher click rates, however, the late preterm infants manifested a moderate prolongation in BAER wave V latency. All interpeak intervals tended to be prolonged at higher click rates. The I-V interval was significantly prolonged at 51/s and particularly at 91/s clicks. Both the I-III and III-V intervals were significantly prolonged at 91/s. The late preterm infants also manifested reduced amplitudes of BAER waves III and V at most click rates.

The central components of the brainstem auditory evoked responses were abnormal at higher click rates three months after term in the late preterm infants. Postnatal brainstem auditory function is suboptimal in late preterm infants without major complications. This suboptimal brainstem auditory function may not be clearly shown at term or an earlier stage, but can be shown later. Late preterm infants, although they may not have major complications, should be followed for later auditory development, providing valuable information for improving postnatal care.