The contribution of maternal smoking to preterm birth, small for gestational age and low birthweight among Aboriginal and non-Aboriginal births in South Australia

Objectives: To determine the contribution of maternal smoking to preterm birth (< 37 weeks' gestation), small for gestational age (SGA, birthweight < 10th percentile for gestational age) and low birthweight (< 2500 g) among Aboriginal and non-Aboriginal births in South Australia. Design: Retrospective cohort analysis of population-based perinatal data. Setting: The State of South Australia, population 1.5 million. Participants: 36 059 women (of whom 851 were Aboriginal women) who had singleton births in 1998-1999. Main outcome measures: Relative risks and population-attributable risks of preterm birth, SGA and low birthweight from smoking in the second half of pregnancy, by age and Aboriginality. Results: Aboriginal women had a higher rate of smoking in pregnancy than non-Aboriginal women (57.8% v 24.0% at the first antenatal visit) and high rates for all age groups, while the rates decreased with age among non-Aboriginal women. Heavy smoking increased with age, and Aboriginal women were heavier smokers. Women who smoked had elevated relative risks of preterm birth (1.64), SGA (2.28) and low birthweight (2.52), and all these showed a dose-response relationship. Among Aboriginal (versus non-Aboriginal) births, population-attributable risks were significantly higher for SGA (48% v 21%, and 59% for births to Aboriginal teenagers), low birthweight (35% v 23%) and preterm birth (20% v 11%). Conclusions: Health promotion programs, with a focus on smoking cessation and reducing uptake of smoking, need to be implemented in an appropriate cultural context, especially among young Aboriginal women. Such a program is being developed in South Australia.