Cohort Profile: The 1987 Finnish Birth Cohort

Abstract

There is ample evidence showing how marginalization and inequalities in well-being and health have roots in childhood.1 Pre- and perinatal factors affect childhood and adolescent outcomes—such as mortality and morbidity,2–5 behavioural problems,6,7 delinquent and criminal behaviour,8 cognitive and motor functioning9–11 and teenage pregnancies,12 but the extent to which these effects are sustained through adulthood is less clear. Epidemiological research has identified various early childhood determinants for social exclusion in adolescence and adulthood. These include pre- and perinatal, genetic as well as environmental risk factors across childhood years.13,14 Problems also run in families as a result of both social and biological processes. There is information about several risk factors that contribute to adolescent mental health problems.15–21 However, little is known about the protective factors. The Finnish welfare system provides many services to children in at-risk groups, yet little is known about the long-term effects of different official actions and at times reports have been unfavourable.22 In addition, significant health differences have been observed according to gender and region, but the reasons for these remain unknown.23,24 Most data on child and adolescent health and social coping are sample based, cross-sectional or based on short-term outcome. The increased routine collection of administrative register data has created new possibilities for life-course epidemiological research. Previously, such data have not been widely used for follow-up purposes. The Academy of Finland launched a research programme on Responding to Public Health Challenges (SALVE) in 2008. This programme is set to provide applicable information in order to respond to current and future key public health issues, and to bring together approaches applied in public health research as well as in behavioural sciences, social sciences and biosciences. The programme is divided into four thematic areas: health-protecting and health-promoting factors, life-course approaches and critical periods of life, health inequalities and clustering of ill health, and predicting future health. Follow-up of the 1987 Finnish Birth Cohort is funded by the consortium ‘Life-course Determinants of Mental Health, Marginalization and Social Coping’ through the Academy of Finland's SALVE research programme. All 60 254 children entered in the 1987 Medical Birth Register (MBR) were included in the first Birth Cohort study covering the years 1987–96, including all live births and stillbirths of infants weighing >500 g or having a gestational age of ≥22 weeks.25–27 After the first Birth Cohort project, it was noted that 185 live-born infants for whom all perinatal information in the MBR was lacking had been born abroad, after receiving more detailed Central Population Register (CPR) information for an internal validation study. These cases were removed, and the number of births in this cohort was finally 60 069. Research evidence is weak as regards providing a basis for understanding life-course development of marginalization and inequalities in health and well-being. In addition, there is very little information on processes of resilience, i.e. good coping and integration into society in spite of adversity during childhood. This information is crucial for successful preventive efforts. With the present data, we can study the development of mental health, behaviour and well-being from childhood to adolescence by using various social and health indicators. Special attention is given to children in at-risk groups who do not develop unfavourable outcomes. In addition, we can test whether, in times of adversity, parental education, functional family relationships and good school achievement predict resilience and good social coping later in life, i.e. in early adulthood. The original cohort data were based on MBR data on perinatal health and on information on maternal health, and diagnoses and interventions during pregnancy and delivery (National Institute for Health and Welfare, THL). The baseline characteristics are shown in Table 1. Baseline characteristics of the study subjects aAccording to Finnish national sex-specific standard. Baseline characteristics of the study subjects aAccording to Finnish national sex-specific standard. The original data were complemented with follow-up information on births and deaths, parents’ marriages and divorces, migration, most recent occupations and dates of death from the CPR. Information on the educational achievements and socioeconomic status of cohort members and their parents was received from the Educational Register (Statistics Finland). The health data consist of information on episodes of specialized hospital care (THL), on sexually transmitted infections (THL), on reimbursed prescribed medicine, special reimbursement rights for long-term medication of certain diseases, child care/disability allowance [Social Insurance Institution (SII)] and on causes-of-death (Statistics Finland). For female cohort members, information on births and induced abortions was collected from the MBR and the Register on Induced Abortions (THL). There was less information on the use of social welfare services. These data included information from the registers on social assistance and children taken into custody (THL). In addition, the Finnish Defence Forces provided information on military service and the results of aptitude tests (mostly boys), and the Finnish Legal Register Centre provided information on criminality. Table 2 shows the main data sources and their main indications. Summary of registers and data in the study Summary of registers and data in the study To complete the cohort information eight separate requests for permission to receive individual-based register data for scientific research (THL, Data Protection Authority, Finnish Defence Forces, SII, CPR, Statistics Finland, Ministry of the Interior, Finnish Legal Register Centre) were sought from the various register authorities and the process took 7 months altogether. It then took a further 18 months to collect all the material from the different register authorities and complete the linkages. Since the research was carried out at THL, their register data were given free of charge. The other authorities charged for their services and the cost for the complete cohort was 10 940 euros (18.4 cents per cohort member). The data for the first Birth Cohort Study were collected in 1994 and it was based on MBR data on perinatal health and on information on maternal health, diagnoses and interventions during pregnancy and delivery, combined with data from five other national administrative registers containing information on demographical background and health (hospitalizations, causes-of-death, special reimbursements for medication and social benefits for care of a sick child) in 1987–94, with regional register data on intellectually disabled subjects in 1996 and with education register data concerning the 38 municipalities in the largest county in Finland in 1996.26 These data were updated with those presented in Table 3, and completed so that the follow-up period ended on the 31 December 2008. Follow-up data of the 1987 Finnish Birth Cohort NA = not applicable. Follow-up data of the 1987 Finnish Birth Cohort NA = not applicable. Follow-up can be continued in the future, but all the current permission documents have to be updated before that. Because of the complexity of the application process and the data themselves, it is feasible to update the cohort data approximately every 5 years. In total, 73 (0.1%) children born in Finland, in 1987, were untraceable because of an incomplete, missing, incorrect or changed identification number. This was 11 more than in the first Birth Cohort Study.28 The remaining number of children included in the follow-up study was 59 996, of which 59 669 were live births and 327 stillbirths. Only the children surviving the perinatal period were included in the study (n = 59 476). During the study period, 497 (0.8%) subjects died and 557 (0.9%) had emigrated permanently by 31 December 2008. These cohort members were included in the study until death or emigration, respectively. The number of cohort members living in Finland on the 31 December 2008 was 58 430 (97.3% of all children born in Finland in 1987). Altogether, 5034 males (16.5%) and 6947 females (23.9%) of the cohort have received some psychiatric care during their lives. Purchases of psychotropic medication were registered for 3003 males (9.9%) and 4847 females (16.7%). In addition, 3110 males (10.2%) and 4601 females (15.8%) have received specialized psychiatric care as outpatients and 1598 males (5.3%) and 1595 females (5.5%) as inpatients. Data on the 1987 Finnish Birth Cohort have recently been completed, and various research activities are under way. Follow-up data on the study population are presented in Table 3. The unique strengths are that the study involves a complete census of all infants born in a single year in Finland and subsequently followed over time. The follow-up includes various detailed forms of documentation of social and health status. Some of the data sources have only recently been open to researchers. The research causes no harm to the participants because it is based on secondary data. No individuals are approached. These data are confidential and do not include any personal identification after linkage. Additional linkage to other data sources is possible, since THL has kept the linkage key for the cohort data. The cohort data can be widely utilized in various research fields including social and health services. The value of the cohort will grow as its members grow older, since follow-up can be continued for as long as needed. The data can also be further extended, for example, with parents’ health status if needed for later studies. However, appropriate licences have to be requested. The main limitation is that we are not allowed to identify people in order to check the validity of the information or to collect additional primary data. The data are also limited as regards psychosocial inheritance. The data are stored and maintained electronically at THL in Finland. We encourage interested parties to make contact with the leader and chief investigator of this study, Prof. Mika Gissler, at mika.gissler@thl.fi, or the study coordinator Dr Reija Paananen, at reija.paananen@thl.fi. Academy of Finland and the National Institute for Health and Welfare.