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Cerebral Palsy in ScotlandChapter contributed by Sandra Bonellie (Napier University) and Jim Chalmers (ISD) IntroductionCerebral palsy (CP) is a term covering a group of disorders, involving motor function, movement and posture that are due to non-progressive abnormality of the brain. There are various ways to categorise CP cases. One method, devised by the Surveillance of Cerebral Palsy in Europe (SCPE) collaboration, suggests four main groups:
Information on children living in Scotland who have been diagnosed with CP is available from the Scottish Register of Children with a Motor Deficit of Central Origin. This register was established by the Public Health Research Unit in Glasgow in 1990 and contains information on children diagnosed from 1984 onwards (Mutch and Ronald, 1992)6. The Information and Statistics Division (ISD) of the National Health Service in Scotland now administers the register. A recent study, funded by the Chief Scientist Office, enabled the CP data for children born between 1984 and 1990 to be linked to the routinely collected maternity data from the Scottish Morbidity Record series (SMR2). This linkage gave access to denominator data thus permitting a retrospective cohort study of births. It also gave additional information on potential risk factors that are not included on the register. This linkage enabled rates and relative risks of CP to be calculated for various factors. Stillbirths and neonatal deaths were excluded from the denominator. The rates reported here are therefore the recorded rates of CP per thousand neonatal survivors. The actual rates may be higher due to the incompleteness of the register. Also, it is highly likely that some babies who were stillborn or died in the neonatal period would have developed CP if they had survived. The number of registered cases of CP born between 1984 and 1990 was 839. Of these, 31 were identified as having postnatal CP and were therefore excluded. Also omitted were cases with a specific syndrome of which CP is a well recognised manifestation, those who were diagnosed before 2 years of age and children whose mothers were not resident in Scotland at the time of the birth. This left 646 cases of which 586 were singleton births and 60 were twin births. Back to topComparison of twins and singletonsIt is well established from previous studies that the incidence of CP is greater in multiple pregnancies than in singleton pregnancies (Pharoah and Cooke, 1996) 7. The following table summarises the results from the Scottish register from 1984 to 1990.
The relative risk of CP in twins compared to singletons is therefore 4.83, (3.80-6.13). Low birthweight and low gestational age are both important predictors of CP as the following table illustrates:
For babies over 2500 grams, the risk for twins is almost 3 times the risk for singletons. For the other categories, the relative risks are less than one, suggesting that the risk of cerebral palsy in low birthweight babies is less in twins that it is in singletons. Overall the rates for twins vary less with birthweight and gestational age than the rates for singletons and therefore the observed higher risk of cerebral palsy among twins cannot simply be attributed to their lower birthweights and earlier gestational ages. Being a twin of itself increases the risk of cerebral palsy. Back to topSmall for gestational ageSince both low birthweight and low gestational age are predictive of cerebral palsy, it might be expected that small-for-gestational-age babies have a higher risk of cerebral palsy. In order to investigate this, centiles for birthweight by gestational age were obtained for singletons using the SMR2 data from the 7 years being studied. For singletons, 19.3% of cerebral palsy cases were below the 10th centile. For twins the percentage was 12.1%. The following table shows this relative risk broken down by gestational age category, together with the risk of stillbirth or neonatal death.
These data appear to suggest that being small for gestational age is protective of CP for singletons who are born before 32 weeks gestation. However the denominator for the cerebral palsy cases consists only of neonatal survivors and this result is most likely due to the higher rate of stillbirths and neonatal deaths in small for gestational age babies. Back to topOther Risk Factors for SingletonsOf the CP cases born between 1984 and 1990, 570 (88.2%) were successfully linked to the delivery records. This linkage gave access to additional information for these cases. The factors that were found to be predictors of CP were: Low birthweight, preterm birth, male sex and a low Apgar score Teenage mothers and those over 35 had higher rates of CP, although only the former was statistically significant. Age remained significant when other factors were taken into account. The risk of CP was also greater for nulliparous mothers but this was not significant when allowance was made for the confounding effect of birthweight and gestational age. The occurrence of maternal infection, premature rupture of the membranes or antepartum haemorrhage were each associated with higher CP rates. These problems can lead to early delivery and were not found to be significant when the rates were adjusted for gestational age. Among term births, there were higher rates of CP for forceps and breech deliveries and for emergency Caesarian sections. The rates were lower for elective sections. The type of delivery was not a significant predictor of CP for preterm births. It was also found that different types of cerebral palsy are associated with different risk factors. The following graph shows the frequency of occurrence of different forms of cerebral palsy by birthweight. Spastic bilateral CP is more common in low birthweight babies, while spastic hemiplegia occurs more often at normal birthweights.
In addition the aetiology of CP was found to be different in pre-term and term babies. In the former, the lower the birthweight and the earlier the gestational age the higher the risk of CP. For this group the occurrence of pre-eclampsia was found to be a protective factor. For term babies, the mode of delivery was found to be important with higher rates of CP among forceps, breech and emergency Caesarean sections and lower rates among elective Caesarean sections. Back to topReferences
Scottish Stillbirth and Infant Death Report 1999 - Full report (pdf file) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cerebral Palsy
Register for Scotland |
