The outcome at 30 months of age is summarized in Figure 1, which is based on the 314 children discharged home and includes all the information available on the 25 children (8 percent) who were not assessed or who were abroad. Table 1 uses these data to show the outcome for the whole study cohort summarized according to gestational age, with the number of live births as the denominator. Two hundred eighty-three children were formally assessed at a median corrected age of 30 months (range, 28 to 40); 90 percent of the assessments occurred between 29 and 32 months.
Bayley Assessments
At least one of the two Bayley indexes could be completed for 251 of the 283 infants (89 percent). The mean score on the Mental Development Index was 84±12, and the score on the Psychomotor Development Index was 87±13. The range of scores according to test scale and gestational age is shown in Figure 2.
On the basis of the lower of the scores on the Mental and Psychomotor Development Indexes, and including the estimated scores of those who were unable to complete the assessment, 53 children (19 percent; 95 percent confidence interval, 14 to 24 percent) had scores more than 3 SD below the mean. These children were classified as severely disabled.11 The scores were from 2 SD to 3 SD below the mean (indicating moderately delayed development) in 32 children (11 percent; 95 percent confidence interval, 9 to 17 percent). These children were assigned to the "other disability" category. The variation in Bayley scores according to gestational age, sex, and single or multiple birth is shown in Table 3. The scores did not vary substantially with gestational age or multiple as compared with single birth, but boys had significantly lower psychomotor scores than girls (mean difference, 5.7; 95 percent confidence interval, 1.9 to 8.6).
Neuromotor Function
Overall, 28 children had severe disabilities of neuromotor function (10 percent; 95 percent confidence interval, 7 to 14 percent), and 39 children had other neuromotor disabilities (14 percent; 95 percent confidence interval, 10 to 18 percent) (Table 3). Of these 67 children, 50 had a recognizable pattern of cerebral palsy (18 percent of the study cohort). The degree of disability in children with each type of cerebral palsy is shown in Table 4. Of the children with cerebral palsy, 27 had severe disability (54 percent). Boys were more likely to have cerebral palsy than girls (P=0.009), but there were no differences related to either gestational age or multiple as compared with single birth.
Sensory Morbidity and Communication Difficulties
Seven children were blind or could see only light; six of these children had received treatment for retinopathy of prematurity (Table 2). Many children had other, less severe, visual impairments: squint was present in 71 (25 percent), and 28 (10 percent) wore eyeglasses. Five children had profound hearing loss that could not be corrected with hearing aids, and a further 36 had lesser degrees of hearing loss. In 18 children there was no recognizable speech at 30 months of age; hearing was normal in 15 of these children.
Severe Disability
Severe disability in the developmental, neuromotor, or sensory and communication domains was present in 64 children (23 percent). Twenty-nine children had disabilities in more than one of the three domains, including 13 with disabilities in each domain. Twenty-seven (10 percent) were classified as having a severe disability on the basis of poor developmental progress without severe neuromotor or sensory and communication problems (only six of these children had no other disability), seven had severe disability in the sensory and communication domain (three of these had other disabilities), and two had severe neuromotor disabilities without severe disability in other domains (both children had quadriplegia).
Head Growth
Head circumference was measured in 278 children (98 percent) and related to United Kingdom population norms. Overall, the mean head circumference was 1.6 SD below the mean for corrected age. Similarly, head circumference was lower in those with any severe disability than in those with no disability (P Among 155 children with no disability, 37 (24 percent) had a head circumference more than 2 SD below the mean.
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