Trends in the rates of cerebral palsy in Victoria, 1983-2002

Trends in the rates of cerebral palsy in Victoria, 1983-2002
SM REID MCLINEPI 1, 3, J CARLIN 1, 3, 4, DS REDDIHOUGH 1, 2, 3
1 Murdoch Childrens Research Institute, Melbourne, VIC;
2Developmental Medicine, Royal Children’s Hospital, Melbourne, VIC;
3 Department of Paediatrics, University of Melbourne, Melbourne, VIC;
4 Clinical Epidemiology and Biostatistics Unit, Royal Children’s Hospital, Melbourne, VIC, Australia

Background/Objectives: There is conflicting evidence world-wide regarding recent trends in the frequency of cerebral palsy (CP) and more studies in geographically-defined populations are required. The aims of this study were to monitor trends in the birth prevalence of congenitally-acquired CP in the Australian State of Victoria, and to describe gestational age-specific trends in the context of changing neonatal intensive care practices.
Design: Prevalence study.
Participants and Setting: Study participants were a population-based sample of children with CP.
Materials/Methods: Data were extracted from the CP Register for cases born between 1983 and 2002 where the brain injury was not acquired post-neonatally. Gestational age-specific denominator data were obtained from the Victorian Perinatal Data Collection compiled from midwives’ statutory birth notifications. Rates of CP were calculated for each gestational age group and for all congenital CP, and Poisson regression models were used to assess trends over time for the same groups.
Results: Between 1983 and 2002, 2367 Victorian-born children with CP were registered, giving an overall birth prevalence of 1.9 per 1000 live births. Following exclusion of 201 children with CP acquired after the 28th day of life, a study group of 2166 children remained. For children born extremely preterm (20-27 weeks), the rate of CP was very high (94/1000 neonatal survivors); these children accounted for 12% of those diagnosed with CP. The number of live births of extremely preterm children rose steadily over the study period, as did the number and proportion of neonatal survivors. Despite the small numbers, the rise in the number of cases of CP in extremely preterm children until the late 1990s was dramatic. There was a gradual increase in the rate of CP per 1000 neonatal survivors up until the early 1990s in extremely preterm infants; since then there has been a gradual decrease. The number of live births of other preterm children (28-36 weeks) increased between 1983 and 2002 but there was no increase in the rate of CP. In contrast, a small rise in the rate of CP for children born at term was seen over the 1980s and early 1990s; since then the rates have decreased. Over the two decades studies, a gradual rise in the overall rate of CP per 1000 neonatal survivors was seen over the 1980s and 1990s for all gestational age groups combined.
Conclusions/Significance: Data from Victoria, Australia, provides some evidence that the gestational age-specific rates of CP are no longer on the rise. However, an increase in the number of live born preterm infants, and improvement in their survival, has resulted in an increased number of preterm children diagnosed with CP over these two decades. Even though preterm infants comprise only around 40% of all CP in Victoria, the disproportionately high frequency of CP in these groups has contributed to a small rise in the rates of CP overall.

 
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