Dear Sir,
Few recognized factors have been associated with childhood cancer. Research has focused on the more common childhood cancers such as leukemia, whereby positive 2-10 and negative associations with birthweight have been found. Other childhood cancers have also been studied with mixed results. The effect of birthweight with regard to the occurrence of childhood cancers has been studied in many case-controls but relatively few population-based cohort studies. This requires reliable population-based birth and cancer registries to enable effective follow-up for outcomes. To our knowledge no prospective population-based study has been conducted in an Asian population. We assess associations of birthweight with the incidence of cancers occurring in Chinese children.Singapore is an island state of about 4 million people. 15 Its population is composed of 3 main ethnic groups: Chinese (76.9%) being the majority, then Malays (14.6%) and Asian Indians (6.4%). All individuals have a unique national registration identity card (NRIC) number. This can be utilized for linkage between or within population-based registries. All births and deaths must be registered in the Singapore National Registry of Births and Deaths (SNRBD). Since 1968 all cancers occurring in Singapore are recorded in the Singapore Cancer Registry (SCR). Details of the registration procedure are well documented. Cancer cases diagnosed in Singapore by medical practitioners and pathology laboratories are notified, and all hospital discharges indicating admission due to cancer are also regularly reviewed by trained registry staff.Quality assurance checks of randomly selected cancers show that the proportion of "death certificate only" (DCO) notifications was 4.2% (for period 1968 -77) and 1.0% (for period 1993-7) thus indicating data of good quality. Our study population consists of Chinese children (i.e., both parents are of Chinese ethnic origin), born between 1 January 1992 and 31 December 1998. Children from multiple births were excluded. Children of the other ethnic groups were excluded because there were too few cancer cases for analysis. Data available from the SNRBD include the child's date of birth, birth weight, gender (male and female), gestational age (weeks) and birth order. The age at the time of the child's birth and ethnic group of both parents were also available. Birth weight was recorded in 500 g categories ranging from Ο½500 to ΟΎ5,000 (11 categories in total). Gestational age is calculated from the first day of the last normal menstrual period. Birth order refers to the numerical order of the child in relation to all previous liveborn issues of the mother. Because of mandatory completion of birth registration, data was virtually complete for the majority of variables for each child.