

* Centre for Child Health Research, University of Western Australia, Telethon Institute for Child Health Research, West Perth, Western Australia, Australia
Department of Neonatology, Childrens Hospital at Westmead, Westmead, New South Wales, Australia
Department of Epidemiology and Public Health, University of Leicester, Leicester, United Kingdom
|| Department of Obstetrics and Gynaecology, Hornsby Ku-Ring-Gai Hospital, Hornsby, New South Wales, Australia
¶ Centre for Developmental Health, Curtin University of Technology, Bentley, Western Australia
| ABSTRACT |
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Methods. A longitudinal follow-up was conducted of a population-based, case-control study of children born in Western Australia between June 1993 and December 1996. The study included 276 term children (
37 weeks gestation) with moderate or severe newborn encephalopathy and 564 unmatched term control subjects. The Griffiths Mental Development Scales was used to ascertain developmental status and a General Quotient (GQ) score. Outcome measures were the Griffiths developmental subscales, GQ, diagnosis of cerebral palsy, and mortality.
Results. Thirty-four patients and 1 control subject died before reaching assessment. Between June 1994 and December 1999, 195 (81%) eligible patients and 445 (79%) eligible control subjects were assessed. Statistically significant differences were found between patients and control subjects for GQ and all developmental subscales. Overall, 39% of patients had a poor outcome as defined by death, cerebral palsy, or a significant degree of developmental delay, compared with 2.7% of control subjects. Furthermore, 62% of those with severe encephalopathy had a poor outcome compared with 25% of those with moderate encephalopathy. Patients with a history of seizures were 3 times more likely to develop cerebral palsy than patients without. Overall, 28 (10.1%) of patients have cerebral palsy.
Conclusions. These data provide important prognostic information regarding survival and serious disability and indicate that newborn encephalopathy places children at significant risk of developmental delay by their second year. These findings also suggest that comprehensive clinical and educational assessments are required to enable appropriate educational provisions as these infants approach school entry.
Key Words: Griffiths Mental Development Scales newborn encephalopathy developmental delay cerebral palsy
Abbreviations: GQ, Griffiths General Quotient SD, standard deviation
| INTRODUCTION |
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| METHODS |
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Patients and control subjects were assessed using the Griffiths Mental Developmental Scales (birth-8 years).18 The majority were assessed between ages 1 and 2 years. The assessments were conducted by 2 trained assessors who were blind to the case-control status of the child. A small number of assessment results were taken from routine Griffiths assessments performed for clinical purposes at the psychology department at the tertiary childrens hospital. Of those eligible, 29% of patients and 31% of control subjects were assessed at home.
The Griffiths General Quotient (GQ) score data for the control subjects were normally distributed. The population mean and standard deviation (SD) for the GQ score were calculated for the control subjects. A cutoff of 2 SD below the control population mean GQ score was used to identify patients and control subjects with a clinically significant degree of developmental delay. The GQ score and Griffith subscale data for the patients were markedly skewed to the left (Fig 2). Median values were therefore compared between patients and control subjects using the Wilcoxon rank sum test for nonparametric data. Odds ratios and their 95% confidence intervals were estimated using the method of Clayton and Hills.19 The formal level of statistical significance was taken as P < .05.
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| RESULTS |
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Griffiths Assessment Results for All Eligible Infants
The results of the Griffiths assessments are given in Table 2 and Fig 2. Statistically significant median differences between the patients and control subjects in the GQ score and the 5 subscales ranged from 6.0 to 8.0 points. These differences represent a median developmental age deficit of 1.5 to 2.5 months for the patients compared with control subjects; the largest deficit was in the speech and hearing subscale. The population mean GQ score estimated from the control subjects was 113 (SD: 9.3). Of the 190 patients assessed, 23.3% had GQ scores below the cutoff of 2 SD below the population mean (94.5 points), compared with 2.5% of the control subjects (P < .001).
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Table 3 and Fig 2 give the results for the patients and control subjects who were assessed having excluded those patients who developed cerebral palsy. Compared with the results for all of the cases, these results were attenuated; however, statistically significant median differences between the patients and control subjects were seen. These ranged from 3.7 to 6.2 points, which represent an overall median developmental age deficit of 1.0 to 1.5 months. The largest deficit was again seen in the speech and hearing subscale. Of the 169 cases assessed, 15.5% had a GQ score below the significant developmental delay cutoff, compared with 2.5% of the control subjects (P < .001).
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| DISCUSSION |
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We excluded the cases with cerebral palsy or conditions known to be associated with significant developmental delay to answer the question most frequently asked by parents: "If my child does not have cerebral palsy, then what is the outlook?" Once these children had been excluded, the differences in development and GQ score between the patients and control subjects were still evident, although not as extreme. Nevertheless, 9% of the remaining patients still had a GQ score that indicated that they had a clinically significant degree of developmental delay.
We were not able to assess all of the patients and control subjects who were eligible for assessment largely because of the vast distances involved in Western Australia. However, even assuming the best-case scenario for those whom we did not assess, the infants with a history of newborn encephalopathy were at a significant developmental disadvantage. Of greatest concern is the impact that the delay will have on future learning and educational attainment. Furthermore, given that we assessed the children at a relatively young age, it is likely that more subtle disabilities and difficulties will declare themselves later, especially at school.
Most previous studies of the long-term outcomes after newborn encephalopathy were conducted some time ago and were concerned mainly with mortality and gross motor impairment.2,3,6 A notable exception is the study by Robertson et al,1 which described other neurodevelopmental outcomes. Nevertheless, the study was restricted to neonates with perinatal asphyxia.1 Other studies in the literature have been smaller and have mainly described infants who have experienced seizures alone810,12 or intrapartum hypoxia.57,11 Most recently, the 1-year outcomes from a prospective cohort study of newborn encephalopathy in Kathmandu, Nepal, have been published.13 In contrast to our study, the authors included children with mild encephalopathy and excluded those with neonatal sepsis, congenital malformations, or primary hypoglycemia. By 1 year of age, 44% of the 131 cases had died; 18% had severe impairments, mostly quadriplegic cerebral palsy; and 2% had minor impairments. They also described an excess mortality (17%) for mild encephalopathy that highlights the differences in the effects of encephalopathy in developing and developed populations where mild encephalopathy has not been associated with death or neurodevelopmental disability.26 In the Kathmandu study, moderate encephalopathy was associated with a 71% risk of severe impairment or death, whereas severe encephalopathy had a 97% risk of death or severe impairment, outcomes clearly much worse than those in our population.
The Griffiths Mental Development Scales were selected as the assessment tool for use in our study because it is the developmental instrument used most widely in Australia, and we anticipated that, in the event that we could not test the child ourselves, we would be able to use the results of testing by another pediatrician or psychologist.27 In addition, the Griffiths Mental Development Scales is an age-adjusted assessment with the 5 subscales of development being equally weighted in difficulty.18 Using an age-adjusted psychometric assessment allows valid comparisons of children at different ages and was therefore an appropriate measure for our cohort of children, who were assessed between the ages of 12 and 24 months.
To date, the limited data available on developmental outcomes after newborn encephalopathy have been inconsistent. The variability in reported findings that used the Griffiths assessments as an outcome measure may reflect the traditional use of a mean GQ of 100 with an SD of 12.2 to determine levels of impairment. It is essential that researchers who use older versions of the Griffiths Mental Development Scales18 remain cognizant of the increase in the general and subscale quotients because the Griffiths was originally standardized in 1950 (02 years) and 1960 (extended 0- to 8-year version). In comprehensive studies undertaken in the 1980s, the Griffiths quotients obtained with the original 1950 and 1960 samples were compared with 1980 samples.28,29 These results indicate that, using the extended 0 to 8 years of the Griffiths, the 1980s sample of 217 children had a mean GQ score of 111.7 and an SD of 12.7 compared with the 1960 sample with a GQ of 100.2 and an SD of 12.8. These differences were statistically significant even after adjustments had been made for a slightly skewed social class distribution and regional differences. It is reassuring that our control population mean GQ was 113 (SD: 9.3), which is in keeping with more recent study results that used the older version of the Griffiths Scales.1,5,2830 Because we had available control data that were from a large random sample of infants born at the same gestation, it seemed more appropriate to use our own control population to define the population mean and determine the cutoff for clinically significant developmental delay.
The patients with a history of severe newborn encephalopathy had a poorer outcome than those with moderate encephalopathy. In part, this is explained by the fact that death in the neonatal period was 1 of the defining features of severe encephalopathy. However, even after excluding the neonatal deaths, twice as many of the patients with severe encephalopathy remained in the poor outcome groups compared with the patients with moderate encephalopathy.
Patients with a history of seizures in the neonatal period had a significantly higher rate of cerebral palsy than those without, although adverse neurodevelopmental outcomes other than cerebral palsy were similar among patients with and without seizures. Recent work by Temple et al8 suggests that seemingly normal survivors of neonatal seizures may have a high incidence of specific learning disabilities and poor social adjustment, which emphasizes the need for careful long-term follow-up of these children.
Although it would have been preferable to be able to present this data broken down by clearly defined causative subgroups, the reality is that in most cases of newborn encephalopathy the exact cause is not known. We previously identified many associations in the preconceptional, antepartum, and intrapartum periods, but the mechanisms of action of these risk factors are currently predominantly unknown and it is by no means certain that all associations are causative. Added to this is the genuine difficulty experienced in clinical practice in adequately defining and diagnosing birth asphyxia and the presence of several subgroups of predisposition among those considered to have asphyxia. Therefore, the clinician is usually left with giving more generic advice to the parents of infants with encephalopathy, and this study seeks to provide a basis for this advice. Future papers will seek to clarify this further by analyzing the data according to the type of risk factors identified and the epoch of pregnancy in which they are likely to be active.
Our findings are important as they provide valuable prognostic information regarding survival and the development of disability. It is important to note that the proportion of children with cerebral palsy is likely to increase, as at the time of this analysis, the youngest children in the study were only 3 years old and the diagnosis of cerebral palsy cannot be regarded as certain until age 5 years. Furthermore, notification to the Western Australian Cerebral Palsy Register is often delayed until the diagnosis is confirmed.
In this follow-up article, we present the only population-based data on developmental outcomes of newborn encephalopathy available in the current literature. Newborn encephalopathy in this study was a clinical diagnosis and was made without assumption or exclusions based on cause.
Our findings indicate the need for continued individual clinical follow-up so that appropriate early interventions and educational provisions can be made or that parents can be reassured that their child is progressing normally and will not require special educational provisions. We are continuing to follow up both the patients and control subjects from our original case-control study. This will allow us to identify the obvious and the more subtle effects that a history of newborn encephalopathy can have on behavior, learning, and cognitive function and to determine their significance as the children grow up.
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| ACKNOWLEDGMENTS |
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G.D. assessed the majority of the children using the GMDS, conducted some of the analysis, wrote the first draft of the paper, and helped plan the follow-up. N.B. conducted the original case-control study; planned, instigated, and supervised the follow-up; and contributed to the analysis and redrafting of the paper. J.J.K. contributed to the original case-control study, supervised and helped plan the follow-up, conducted most of the analysis, and contributed to the redrafting of the paper. J.M.K. contributed to the original case-control study and contributed to the redrafting of the paper. S.S. helped plan the follow-up, provided clinical supervision for the follow-up assessments, and contributed to the editing of the paper. S.R.Z. helped plan the follow-up, provided clinical supervision for the follow-up assessments, and contributed to the editing of the paper. F.J.S. conceived the original case-control study, helped plan the follow-up, and contributed to the editing of the paper.
We thank the children and parents who participated in this study and the staff of the Telethon Institute for Child Health Research and the Princess Margaret Hospital for Children. We are also grateful to the contributions of Jane Doyle, Fiona OSullivan, Margaret Baron-Hay, Patrick J. Pemberton, Linda Watson, Sharon Vukovich, Gail Reading, and Peter Cosgrove.
| FOOTNOTES |
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Reprint requests to (G.D.) Telethon Institute for Child Health Research, Box 855, West Perth WA 6872, Australia. E-mail: glenysd{at}ichr.uwa.edu.au
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