Effect of gestational age misclassification on the pattern of low birthweight in Aborigines

Are most births of Aboriginal babies with low birthweight preterm or full term? There is no consensus because of the difficulty in obtaining valid measurements of gestational age. In Queensland, between 1988 and 1992, there were 519 births of Aboriginal babies with low birthweight in excess of the number expected if aborigines had the same risk of low birthweight as whites. Most of these were preterm (males 76 per cent, females 65 per cent). Sensitivity analyses were used to investigate whether this result was robust to gestational age misclassification. Implausibly large misclassification proportions were required to make preterm low birthweight an insignificant contributor to the low birthweight excess in Aborigines. Therefore, efforts to reduce the number of preterm births should be given high priority. Unfortunately, significant reductions in the number of preterm births will not be achieved by reducing the prevalence of traditional risk factors for full-term low birthweight (for example, maternal smoking, teenage pregnancy). More work is needed to identify potentially modifiable risk factors for preterm birth.