THE COGNITIVE OUTCOME OF VERY PRETERM INFANTS MAY BE POORER THAN OFTEN REPORTED - AN EMPIRICAL-INVESTIGATION OF HOW METHODOLOGICAL ISSUES MAKE A BIG DIFFERENCE
D. Wolke et al., THE COGNITIVE OUTCOME OF VERY PRETERM INFANTS MAY BE POORER THAN OFTEN REPORTED - AN EMPIRICAL-INVESTIGATION OF HOW METHODOLOGICAL ISSUES MAKE A BIG DIFFERENCE, European journal of pediatrics, 153(12), 1994, pp. 906-915
The effects of relying on outmoded IQ-test norms and the use of arbitr
ary classifications of developmental delay on estimates of cognitive i
mpairment of very preterm infants (VPI) was evaluated in a prospective
population study. Cognitive assessments included the Griffiths test a
t 5 and 20 months and the Columbia Mental Maturity Scales (CMM) and a
vocabulary test (Aktiver Wortschatz Test, AWST) at 56 months of age. R
ates of cognitive impairment of 321 very preterm infants (VPI; < 32 we
eks gestation or < 1500g birth weight) were determined according to th
e published test norms, to scores of a full-term control group (FC n =
321), and to scores from a representative sample of children (NC n =
431) of the same birth cohort. IQ-scores were higher in the FC and NC
children than in the original standardisation sample (SS). Using the c
oncurrent test norms (FC, NC) up to 2.4 times more VPI were identified
as seriously impaired (<-2 SD) than if the published (outdated) norms
were used. Serious developmental delay was underestimated when arbitr
ary (e.g. DQ < 70) rather than across age comparable definitions (DQ <
-2 SD) were used. VPI study drop-outs had mothers with lower education
al qualifications and poorer cognitive developmental scores at 5 or 20
months of age. In conclusion, a lack of appropriate control groups an
d use of arbitrary criteria for judging serious delay leads to large u
nderestimations of cognitive impairment in VPI. Findings from previous
uncontrolled studies of VPI need re-interpretation.