Little information is available regarding the behavioral repertoire of heal
thy, yet prematurely born, infants. To address this problem, the Assessment
of Preterm Infants' Behavior (APIB) was used 10 to 14 days after birth in
a cross-sectional comparison of 42 healthy newborn infants: 16 full-term in
fants (gestational age at birth [GA] = 40 weeks), 13 close to full-term inf
ants (GA = 37 weeks), and 13 preterm infants (GA = 34 weeks). Groups differ
ed on four background variables that were used as covariates in subsequent
analyses. Significant group differences were found on 12 of 29 outcome vari
ables, including measures of autonomic, motor, state, attention/interaction
, and self-regulatory systems, as well as a measure of overall behavioral o
rganization. Pairwise comparison showed that preterm and full-term infants
differed on all 12 variables whereas preterm and close to full-term infants
differed on 11 of the 12 variables. Furthermore, full-term and close to fu
ll-term infants differed on 4 of the 12 variables, including measures of th
e autonomic, motor, and state systems. Full-term and close to full-term inf
ants were behaviorally more similar to one another than either group was to
the preterm infants, yet there were important differences even between ful
l-term and close to full-term infants.