This paper addresses the question of whether corrected age needs to be
applied to both the mental and motor development of preterm infants d
uring the whole of the first year. A neglected problem in this respect
is that a precise developmental index cannot be found with very low o
r very high raw scores. Using an alternative measure of performance (a
ge equivalent deviation score), 36 preterm infants without serious med
ical or neurological problems were compared with 21 full-term infants
on the Dutch version of the Bayley Mental Scale at the corrected ages
of 12, 18, 24, 39 and 52 weeks and the Psychomotor Scale at 24, 39 and
52 weeks. Our findings suggest that full correction should be used in
assessing the mental development of relatively healthy preterm infant
s during the second half of the first year. Assessments at earlier age
s seem to overestimate the mental abilities of preterm infants, thus i
ndicating that partial correction should be applied at these ages. For
motor development during the second half of the first year a partial
correction would seem more appropriate. The clinical implications of o
ur findings are discussed.