Low birthweight and socioeconomic status, Victoria 1982 to 1986

Abstract

The aim of this study was to evaluate the association between the incidence of low birthweight and socioeconomic status, in particular whether the relationship was different for very low birthweight (less than 1500 g) and moderately low birthweight (1500 to 2499 g). The study population was births from 1982 to 1986 to women resident in Victoria (300,704). Data on socioeconomic status were derived from an indicator developed by the Australian Bureau of Statistics from the 1981 census and applied to postcodes. Using the rates of very low birthweight and moderately low birthweight in the highest socioeconomic status decile as the reference value we found that the relative risk for very low birthweight was significantly raised in only the lowest socioeconomic status decile (relative risk = 1.29, 95% confidence interval (CI) 1.17 to 1.42). The relative risk for moderately low birthweight was increased in the two lowest deciles: 1.19 (CI 1.12 to 1.26) and 1.09 (CI 1.01 to 1.17) respectively. Women not married at the time of the birth had a higher rate of low birthweight and were more likely to live in the lower socioeconomic status postcode areas. The relationships between very low birthweight, moderately low birthweight and socioeconomic status were attenuated but still significant when this factor was taken into account. Differences in low birthweight by socioeconomic status decile were not apparent for nonsmoking women. The relationship between smoking and low birthweight was different in the two lowest socioeconomic status deciles: the relative risk of low birthweight in smokers was 2.60 (CI 1.73 to 3.91) compared with a relative risk of 1.64 (CI 1.33 to 2.03) in deciles 3 to 10.