Most people in Hong Kong remember 1997 to be a significant year because of the handover of Hong Kong back to the People's Republic of China from the former British colonial power. However, for a small group of researchers from The University of Hong Kong and the Department of Health, Hong Kong Special Administrative Region, 1997 was the year that one of Asia's largest birth cohorts was established.
Given the smoking epidemic in China and the strong presence in the field of tobacco control of the department of Community Medicine at the Faculty of Medicine, the study was originally designed to provide high quality evidence concerning the impact of second hand smoking on infant health. This study funded by the Health Care and Promotion Fund of Hong Kong launched the birth cohort.
The birth cohort were recruited at the first postnatal visit to any one of all of the 47 Maternal and Child Health Centres. In Hong Kong families of newborns are encouraged to attend these centres for free postnatal care and to continue with regular follow-up visits for free developmental checks, physical examinations and vaccinations until the age of six years. Information on socio-economic status, birth characteristics, infant feeding, second hand smoke exposure and health services use was collected at the initial or subsequent visits using self-administered questionnaires in Chinese.
Our study recruited 8327 infants which accounted for 88% of all births in Hong Kong in April and May 1997. Active follow-up continued until 18 months of age, with questionnaires at regular intervals (3, 9 and 18 months), supplemented by telephone interviews where necessary. Follow-up of the birth cohort was restarted in 2005 using record linkage to information routinely collected by governmental agencies, such as the Family Services, the Student Health Service and the Hospital Authority. Since 2007, direct contact has also been re-established with most of the birth cohort families in preparation for more active follow-up at regular intervals.