Behavioral and electrophysiological evidence for gestational age effects in healthy preterm and fullterm infants studied two weeks after expected due date.

We investigated the effects of gestational age at birth on behavioral and electrophysiological measures of 135 medically healthy infants, studied at 42 weeks postconception, and stratified into 3 groups--early-born preterms, 26-32 weeks (n = 55); middle-group preterms, 33-37 weeks (n = 43); and fullterms, 38-41 weeks (n = 37). Subjects were studied behaviorally with the Assessment of Preterm Infants' Behavior (APIB) and electrophysiologically with brain electrical activity mapping (BEAM). Fullterms showed significantly better behavioral function than both preterm groups. Less difference was found between the preterm groups. EEG spectral and photic evoked response were of significantly less amplitude for the preterms than the fullterms. Path analysis showed gestational age effects on behavioral (3 of 6) and electrophysiological (13 of 17) variables due to postnatal complications. We conclude that some differences attributable to gestational age at birth are explained by the cumulative effect of minor but unavoidable complications associated with premature birth. We speculate that remaining effects may result from developmentally inappropriate sensorimotor stimulation consequent to the premature experience of an extrauterine environment.