Discussion
This study showed that DCD is still common in 11-year-old children born very preterm in 2000s. Children born very preterm with DCD had worse cognitive development than children born very preterm without motor impairment. Moreover, children born very preterm with DCD reported lower HRQoL than children born very preterm without DCD. However, the HRQoL was higher in this study cohort of children born very preterm than in Finnish norm population.
The finding of a high rate of DCD in children born very preterm in early adolescence is parallel to the recently reported rising trend of non-CP motor impairments in children born extremely preterm at the age of 6.5 and 8 years.7 21 The rate of DCD in children born extremely preterm of this PIPARI study cohort was 18%, while two recent studies from Sweden and Australia have reported non-CP motor impairment rates of 26%–37% in extremely preterm populations.7 21 The Swedish study reported that the rate of non-CP motor impairment was 37% when they used a cut-off based on their control group, but if the normative cut-offs32 had been used the rate would have been 12.5%. Some studies have reported the prevalence of non-CP motor impairment as being higher in boys,7 12 while others have shown no significant difference in the prevalence in boys and girls.21 In the present study, all but one of the children with DCD were boys. However, the small number of children with DCD did not enable reliable statistical analysis regarding sex.
A positive correlation between motor outcome and cognitive development in children born very preterm was found even if the correlations were not strong in magnitude. Children born very preterm with DCD had lower mean scores in the Full-Scale IQ and in all indexes compared with children born very preterm without motor impairment. The differences were clinically significant in magnitude, that is, 15 points for Full-Scale IQ, 8 points for verbal comprehension, 9 for perceptual reasoning, 16 for working memory and 13 for processing speed, all in favour of children without DCD. This is in line with previous studies that have reported lower Full-Scale IQ and processing speed in children born very preterm with DCD at 5 years of age22 and lower perceptual reasoning and processing speed in children born extremely preterm with DCD at 6.5 years of age.21 However, as WISC-IV has some items in the processing speed and the perceptual reasoning index subtests requiring fine motor control (eg, holding a pen, drawing in a small space and manipulating blocks), it is possible that motor impairment may have an effect on the child’s performance in these subtests. According to our results, DCD might also indicate problems in cognitive development at 11 years of age in children born very preterm. Lower motor scores accumulated among boys born very preterm in the present study. Future research may expand current findings about possible mechanisms leading to vulnerability according to sex.
This study showed lower self-experienced HRQoL in children born very preterm with DCD compared with children born very preterm without motor impairment in early adolescence. The affected domains were vision, hearing and speech. The absolute differences in HRQoL results between the groups were minor since the scoring system ranges from 0 to 1. Whether these statistically significant differences have clinical importance is not definite. A previous review using various instruments suggested difficulties in fine motor skills (and causing difficulty, eg, with brushing teeth, washing hair, dressing up and using knife and fork) and in social skills (causing, eg, loneliness and spending more time alone).39 Nevertheless, comparing different instruments should be treated with caution. Self-experienced HRQoL at 11 years of age was better in our study cohort of children born very preterm compared with the test normative at the same age in the Finnish population. This is an unexpected finding as children born very preterm have many impairments potentially lowering their HRQoL. The mothers of the children who withdrew from the study had lower educational level compared with the mothers of the study children. This may have influenced the results and may offer one explanation why the study cohort of children born very preterm reported their HRQoL better compared with the norms. However, we are not aware of differences in general health outcomes in the 1990s and 2000s. In any case, good HRQoL in children born very preterm at 11 years of age is a reassuring information for families with a preterm infant.
The strength of this study was its relatively high follow-up rate (78%) from birth to 11 years of age. The examinations were performed with the latest version of the Movement ABC-2, and a thorough Touwen neurological examination was used to support the definition of DCD. A possible limitation was that the motor assessments were not done repeatedly as suggested by the latest European Academy of Childhood Disability recommendations.12 However, these new guidelines were not available during the data collection. We also chose to use the strict cut-off of fifth percentile to define clinically significant non-CP motor impairment. There was no possibility to compare the rate of DCD with peers born at term due to lack of a control group. To assess cognitive development we used WISC-IV, which is a validated and widely used tool in Finland, and the national cut-offs are precise and up-to-date. Regarding HRQoL, the results the Finnish normative of the same age population were available, although these were based on data collection before 1996. Although the sample size of the whole study group was satisfactory, the total number of children born very preterm with DCD and CP was small, which restricts the power of the statistical analysis concerning these groups and the generalisability of the results.