Background

   To improve child health, understanding its determinants is important not only at individual, but also at family, community and social level. However, the influence of the social environment and how it works together with other factors to impact child health remain understudied, particularly in Taiwan. Notably, during the 2000s, several social changes occurred, such as rising female labour-force participation, delayed age of marriage and increased transnational marriages; therefore, 
investigating whether, how and up to what extent these changes in social environments contribute to child health is crucial.

   From ‘life-course perspectives’, child health and early-life experiences impact adult health because of the interconnections of experiences and developments in different stages of life. Therefore, health needs to be considered as both an outcome of former life-course processes and a determinant of latter life-course processes. The Taiwan Bureau of Health Promotion, Department of Health [reformed into the Taiwan Health Promotion Administration (HPA), Ministry of Health and Welfare, in 2013] commissioned a nationwide longitudinal study in 2003. This study was launched as the Taiwan Birth Cohort Study (TBCS) and was designed to establish national norms of children’s development according to socioecological and life-course perspectives.

Aim of the Survey

• To record and assess the health trajectory of Taiwanese children born in the 
  twenty-first century
• To investigate the influence of the social environment on child health
• To examine the association between child health and subsequent health outcomes in 
  adulthood

Sampling and Survey Method

   A two-stage stratified random sampling method was used to select a representative population-based birth cohort in Taiwan from the National Birth Report Database, with the township as the primary sampling unit and newborns as the secondary sampling unit. In the first stage, the 369 targeted townships were stratified into 12 strata according to the degree of urbanization and total fertility rate.
We used a systematic random sampling technique to select 89 townships. In the second stage, newborns were directly drawn from the sampled townships with the probability proportional to size sampling method.

    Initially, 24,200 newborns were selected from live births in Taiwan during 1 January 2005 to 31 December 2005. They were first approached by postal mails notifying their opportunities to participate in the study. The notification mail also included a brief introduction of TBCS along with the specific date and time scheduled for the face-to-face interview. The participants could refuse participation or reschedule the interviews by calling the research team.

    Finally, baseline data collection was performed for 21,248 (87.8%) newborns when they were at the age of 6 months and they were thus recruited as cohort members.

Follow-up surveys were conducted thereafter.

Content of the Survey

   The content of the questionnaire covers a wide range of information about social and physical exposures of the children in relation to family, neighborhood, and institutions such as child care. Children’s wellbeing, including physical growth, psychosocial development, and health conditions, is also recorded in each survey. 
The survey instruments from the first to fourth waves were as follows: Infant/Child Health Care Needs Survey (referred to as the Main Survey), Child Development Scale and 36-Item Short Form Survey (SF-36) for parents. A school questionnaire was further administered in the 8- and 12-year surveys. In addition, self-reported data were collected from the cohort members in the 12-year survey and thereafter.

   Till now, abundant information was further obtained. Data on physical and mental health, lifestyles, school life, peer relationships and parent–child interactions were collected using the face to face interview and self-reported questionnaire. A pilot test of changing survey mode from paper and pencil to web-based online questionnaire was conducted in 2022.

 
Survey Result
Part of the survey results were included in the Statistics of Health Promotion. 
(Please visit the website at
 https://www.hpa.gov.tw/EngPages/List.aspx?nodeid=3850). More information about 
the cohort study is available in the Cohort Profile published in the International 
Journal of Epidemiology in 2021 ( DOI: 10.1093/ije/dyab048 )