Background EEG activity in preterm infants: correlation of outcome with selected maturational features.

The aim of this study is to identify normal EEG patterns of preterm infants, characteristic of early postmenstrual ages (PMAs). Quantitative features of EEG background activity have been examined in records from 83 preterm infants within the first 2 weeks of life at a PMA of 27-34 weeks. These subjects presented different cranial ultrasound findings and different outcomes. EEG quantitative data have been compared to the subsequent neurological evolution. We supposed that the features of EEG background activity which were associated with a favourable outcome should be considered as indexes of "normality" of the tracing for that specific PMA. At 27-30 weeks of PMA a high incidence of "temporal sawtooth," a particular rhythmic theta activity detectable in temporal regions, relates to a favourable evolution, therefore it can be assumed that this activity is a normal feature of EEG tracings at this age. On the contrary, a significant correlation between a high incidence of "temporal sawtooth" and an abnormal outcome is observable at 33-34 weeks and leads us to deduce that this pattern should disappear at this time. After 31 weeks other parameters (such as the incidence of 8-20 Hz activities, the length of the intervals and burst duration) show a significant correlation with the outcome.