SOMATOSENSORY EVOKED-POTENTIALS IN TERM AND PRETERM INFANTS IN RELATION TO POSTCONCEPTIONAL AGE AND BIRTH-WEIGHT

The effect of age on the maturation of median nerve somatosensory evoked potentials (SEPs) was studied in 103 normal neonates (24 preterm, 79 term) at the postconceptional age (PCA) of 36-48 weeks. The influence of birth weight was evaluated in 44 term neonates, aged 0-7 days, according to their gestational age (GA) stratified into three groups: A: 38-39 weeks (n = 15); B: 39.5-40.5 weeks (n = 15); C: 41-43 weeks (n = 14). The mean birth weight was not different in the three groups. For all infants the N13 latency recorded at cervical 8CS2-Fz) level as well as the N19 onset and peak latency at cortical (C3'/C4'-Fz) level were measured. For these parameters and for the N13 latency divided by arm length (N13/AL) and the N19 ascending time (N19AT) the P50, P97 and P3 were calculated as a function of PCA. They were all decreasing in the 36-48 weeks period, fast before 40 weeks and slowly thereafter. The SEP values of groups, A, B and C were not different, but in each group the wave pattern of the cortical SEPs was more mature in the larger than in the smaller infants. For the groups A, B and C together birth weight (in SDS) correlated inversely with the N13/AL and the N19AT (both in SDS) (r = 0.73 and 0.52 respectively, p < 0.001). Our data indicate that the progression of maturation of the various SEP components in the period of 36-48 PCA is non-linear. The peripheral and central nervous system of small, term infants is less mature than that of large newborns of the same gestational age. The SEP method can sensitively record this gradually increasing maturation in a group of infants with normal birth weight.