Trends in Prevalence and Comorbidities of Children With Cerebral Palsy in Norway

Cerebral palsy (CP) is the most common cause of permanent motor disabilities in children, and one of the patient groups that receive the largest proportion of health care resources in high-income countries. CP is the result of a non-progressive injury in the immature brain that occurs before, during or after birth (neonatal period). The injury may be caused by a congenital brain abnormality, infection, trauma or other complications. Known risk factors include premature birth, restricted fetal growth and lack of oxygen during birth (birth asphyxia). Research shows that the panorama of causes has changed over time.

The clinical characteristics of CP vary considerably, something one would expect from the variation in potential causes. CP is categorized into subtypes based on the dominating symptoms and which part of the body is affected. Further classification is often based on the severity of the child's motor impairment. Also, children with CP often have additional comorbidities such as epilepsy, impaired vision and/or hearing, impaired ability to speak/communicate, cognitive disorders, and nutritional problems. Nor in these areas has the situation remained static over time.

During the last 20 years, both obstetric and neonatal care has undergone significant changes in Norway as well as in other countries. In the 1990s surfactant treatment of premature children was established, and in the early 2000s, therapeutic hypothermia was introduced as a new treatment for term born children with hypoxic ischemic encephalopathy (HIE). There have also been improvements in fetal monitoring during labor from around 2004 with an increase in the use of continuous electronic monitoring of the fetal heart using either the cardiotocography (CTG) or ST analysis (STAN) method to assess the baby's well-being, as well as Fetal scalp pH testing to determine if the baby is getting adequate oxygen supply. In this project, the investigators intend to study if the introduction of these new treatments has been associated with a decrease in the prevalence of CP and in changes in the clinical picture (e.g. less serious motor disabilities and comorbidities) for children born 1996 to 2010.

To study these questions, the investigators will take advantage of data from three national health registers: The Medical Birth Registry of Norway (MBRN), The Norwegian Patient Registry (NPR) and The Cerebral Palsy Registry of Norway (CPRN). While the MBRN has recorded all births since 1967, the NPR has recorded all patients treated in special health care service since 1997 and with their national identification numbers since 2008. All children with CP are diagnosed and their treatment assessed at pediatric habilitation centers, reporting to the NPR. The CPRN is a national medical quality register, owned by the South-Eastern Norway Regional Health Authority, and is located at the Vestfold Hospital Trust. Participation in the CPRN is based-on parental informed consent. This register has systematically recorded children with CP born since 1996, and has received high scores by The Norwegian Advisory Unit for Medical Quality Registries (SKDE). Moreover, the investigators have recently documented completeness and correctness of CP diagnoses in the CPRN as well as in the NPR. Thus, the use of data from these three high quality health registries provides a unique opportunity to study on a population level if the new obstetric and neonatal treatment options have been followed by measurable reductions in the prevalence of CP.

The purpose of the Cerebral Palsy Registry of Norway is to increase knowledge of the causes and treatment of children and youths with CP through surveillance and systematic analyses, including to:

• Describe the prevalence of CP in Norway, including subtypes, severity and comorbidities
• Improve the quality of pregnancy care and newborn medicine
• Ensure equal treatment and follow-up of children/youths with CP in Norway, regardless of place of residence.
• Increase knowledge of CP

This study fulfills all of these aims, and also has the potential to go one step further and impact children at risk for CP. By gaining better knowledge of children with CP in Norway during this study period, the investigators can explore variations in the causes and treatments for newborns at increased risk of CP and children with CP, per health region and/or per health trust.

The overall design of this project is a register-based population study, comprising of three sub-studies.

Study 1: Completeness and correctness of the CPRN and NPR There was a variation in the reported prevalence of CP in Norway from different data sources used to identify children with CP. The aim of this study was thus to combine data sources and to validate the CP population in Norway for children born 1996-2007, and thereby gain an accurate estimate of the prevalence rate of CP in Norway. This study was published in March 2017. A second validation study of CP diagnoses for children born 2007-2010 and registered in the CPRN and/or NPR was completed in January 2017.

Study 2: Trends in prevalence, causes, diagnostics and clinical characteristics of children with cerebral palsy born in Norway 1999 to 2010.

The aim of this study will be to examine whether there has been a decrease in the prevalence of CP and changes in the clinical picture (e.g. less serious motor disabilities and comorbidities) following new standardized methods of obstetrical care, such as fetal monitoring during labor, as well as of intensive care of sick newborns introduced in Norway during the last 20 years.

Data for 707 916 children born in Norway between 1999 and 2010 have been registered in the MBRN. Of these, 1664 children have been confirmed to have CP and are registered in the CPRN. A data linkage of the MBRN and CPRN was performed in February 2017. The MBRN includes data on a number of well-known and unknown risk factors for CP (e.g. length of pregnancy, Apgar scores, congenital malformations, intrauterine growth retardation, etc.). The CPRN contains information on the clinical picture of CP at five years of age (gross, fine and oral motor function, cognition, epilepsy, eating abilities, and magnetic resonance imaging findings).

Logistic regression using fractional polynomials will be used to estimate time trends in prevalence rates with 95% confidence intervals (CI), according to Altman et al. Differences in proportions of clinical characteristics will be analyzed by χ2 linear-by-linear association or Cochran-Armitage test for trends. A p-value below 0.05 is considered statistically significant.

Data analysis began in early 2017, and an article is currently being finalized.

Study 3: CP and comorbidities Data from the NPR will be used, including administrative (treating institution, consultation and/or hospitalization, patient place of residence) and medical (diagnosis and treatments codes) and social (housing situation and care situation) data on all children born 1996-2010 that have received treatment in specialist health services since 2008. Children with CP will be compared to children without a CP diagnosis. The main aim of this study will be to describe frequencies of comorbidities that occurred before and after children are diagnosed with CP. Logistic regression analyses will be used to compare children with CP to the general population. This study is a follow-up study in collaboration with the Norwegian National Institute of Public Health, which recently published a study on Comorbidity and Childhood Epilepsy: A Nationwide Registry Study.