[EEG of the very premature infant born at 24 to 30 weeks gestational age. Definitions and normal area].

This article aims at summarizing normal EEG criteria and their maturational pattern in premature infants of 24 to 30 weeks gestational age. Although very premature infants with a normal outcome are not numerous, their normal EEG patterns must be known, as EEG constitutes a basis for neurological prognosis. Background activity is first discontinuous. Discontinuity decreases thereafter with increasing age, so that some long periods of continuous activity may be observed in active sleep, around 30 weeks of age. Conversely, interburst intervals become shorter and the proportion of time without EEG activity is decreasing. Based on EEG activity and eye movements, a rough sleep-state differentiation was described as soon as 25 weeks of gestational age and is completely achieved at 30 weeks. The main EEG figures are high-voltage delta waves of higher amplitude and slower frequency in younger infants. Temporal delta waves occur in sequences, these are very characteristic of the very premature infant; thereafter, they become smaller, less numerous and eventually disappear around 27-28 weeks. In contrast, occipital delta waves remain numerous and of high voltage, are usually bilateral and superimposed with fast rhythms. The two types of frontal delta waves that are observed in 24-27 weeks prematures disappear with maturation. Bursts of synchronized delta waves are less numerous than localized delta waves and also disappear before 28 weeks of age. Finally, diffuse theta bursts are mainly recorded at 26-27 weeks GA and become more localized in temporal areas with maturation. At 30 weeks, they are observed on temporal areas, mainly during slow-wave sleep.