Aim: To clarify further the influence of intrauterine growth retardation (IUGR) on early neural development. Methods: In 30 small‐for‐gestational age (SGA) preterm infants at term, brainstem auditory‐evoked responses (BAERs) were recorded with clicks of different repetition rates. All infants had a birthweight >3rd centile, without any other major perinatal complications. Results: Compared with the BAER in 36 appropriate‐for‐gestational age (AGA) term infants, the preterm SGA infants did not show any abnormalities at 21 s−1 clicks, except for a slight increase in wave III amplitude. At 51 s−1 clicks, there was an increase in III–V/I–III interval ratio (ANOVA p < 0.05). At 91 s−1, the I–III interval shortened, whereas the III–V interval and III–V/I–III interval ratio increased (all p < 0.05). Wave V amplitude tended to increase slightly at all repetition rates of clicks used, although this increase did not reach statistical significance. The III–V interval and III–V/I–III interval ratio in the preterm SGA infants at different click rates correlated inversely with occipitofrontal head circumference at the time of testing, i.e. the smaller the head the longer the III‐V interval (all p < 0.01). Wave III amplitude at 21 s−1 also correlated inversely with head circumference (p < 0.01), suggesting that the slight increase in this amplitude in the preterm SGA infants is related to their relatively small head size. Conclusion: There were no major abnormalities in the BAER up to 91 s−1 clicks at term in preterm SGA infants. The slight increase in III–V interval at high‐rate stimulation suggests a subtle degree of central neural dysfunction, which is associated with small head size following IUGR.
Aim: To examine the process of change in hearing threshold during the neonatal period after perinatal hypoxia‐ischaemia. Methods: The threshold of brainstem auditory evoked responses (BAER) was measured serially during the first month after birth in 92 term babies who suffered hypoxia‐ischaemia. Results: The mean BAER threshold in these babies was significantly increased on day 1 (ANOVA p < 0.001). The elevated threshold decreased progressively on days 3 and 5, but was still significantly higher than that in normal controls (p < 0.01). The elevation continuously decreased more slowly on days 10 and 15, and to a near normal level on day 30. Threshold elevation was seen in 31.7% of the babies on day 1, and 34.5% during the first three days. The rate of elevation decreased progressively thereafter. On day 30, 10.6% of the subjects still had increased thresholds. Moderate to severe elevation occurred mainly during the first week and severe elevation occurred predominately on day 1. Threshold elevation starting after days 3–5 is likely to be due to middle‐ear disorders. As a whole, during the first month, 44.6% (41/92) of the babies studied had threshold elevation. BAER threshold was correlated weakly with the stage of hypoxic‐ischaemic encephalopathy on days 1 and 3. The threshold was significantly higher in babies with severe encephalopathy than in those with mild or moderate encephalopathy during the first 3 d of life. Conclusion: Hearing threshold is elevated in about one‐third of term babies after hypoxia‐ischaemia. The elevated threshold decreases progressively after birth, and returns to normal by one month in most babies. The threshold correlates weakly with the severity of encephalopathy.
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