• Air pollution;
  • pregnancy;
  • preterm birth

Background  There is evidence that maternal exposure to ambient air pollution during pregnancy is associated with adverse birth outcomes.

Objective  To assess preterm birth (PTB) in relation to maternal exposure to ambient air pollution.

Design  Retrospective cohort.

Setting  Brisbane, Australia.

Sample  A total of 28 200 singleton live births for the period of 1 July 2000 to 30 June 2003.

Methods  Average maternal exposure estimates for ambient particulate matter (PM10 and bsp), ozone (O3) and nitrogen dioxide were calculated over the first 3 months after last menstrual period (LMP) and the last 3 months prior to birth (individually and combined as trimesters).

Main outcome measures  PTB was defined as gestation <37 weeks and odds ratios (OR) were calculated for PTB per interquartile range increase in the maternal exposure estimate for each pollutant. Various covariates were controlled for, including season of birth.

Results  Exposure to PM10 and O3 during trimester one was associated with an increased risk of PTB (OR = 1.15, 95% CI 1.06–1.25 and OR = 1.26, 95% CI 1.10–1.45, respectively). The PM10 exposure effect associated with trimester one was strongly related to exposure during the first month post-LMP (PM10, month one; OR = 1.19, 95% CI 1.13–1.26).

Conclusion  These results suggest that maternal exposure to low levels of ambient air pollution is associated with PTB.