Objective The amplitude EEG (aEEG) has been increasingly applied in premature infants, especially in pathological conditions. However, information on the aEEG longitudinal changes in growing and neurologically normal premature infants is limited. Our aim was the surveillance of the evolution of aEEG activity in premature infants and the effect of extrauterine life on its maturation.

Methods 96 neonates (gestational age 26–34 weeks) without evidence of neurological abnormalities were studied with aEEG, starting at admission and then weekly until hospital discharge. The infants were divided into three groups according to gestational age: group A 26–29 (27.66 ± 1.1) weeks, n  =  30; group B 30–31 (30.65 ± 0.5) weeks, n  =  41 and group C 32–34 (32.44 ± 0.7) weeks, n  =  25. aEEG tracings were evaluated concerning continuity, cycling, amplitude of the lower border and bandwidth.

Results In total, 514 aEEG traces were assessed. All groups displayed progressive maturation of every one aspect of the aEEG after birth. There was an increase in the continuity, more frequent and more clearly defined cycling, elevation of the amplitude of the lower border and narrowing of the bandwidth, proportional to both gestational and postnatal age. The comparison of the three groups at the age of 32 weeks revealed significant acceleration of maturation with regard to cycling and bandwidth (p<0.000 and p<0.007, respectively). The younger the gestational age of the infant, the quicker the process of aEEG maturation.

Conclusions The evolution of the aEEG of preterm infants is influenced by the gestational age and postnatal age. The exposure of the premature infant to environmental stimuli seems to accelerate the maturation of the aEEG tracing.