Introduction: There are no reported studies on the effects of ambient air pollution on birth outcomes from Australia. We therefore undertook an investigation to determine if there were any associations between ambient air pollutants (particulate matter, nitrogen dioxide and ozone) and gestation. The study was conducted in Sydney, Australia.
Methods: The study period was a three-year period between 1998 and 2000 and included all births in metropolitan Sydney in this time period. We used routinely collected data for both the exposures and birth outcomes. We obtained the perinatal data from the New South Wales Health Department and air pollution data from the New South Wales Environment Protection Authority. Birth data included demographic factors (age, smoking status, country of birth, postcode of residence at time of delivery), pregnancy factors (date of the last menstrual period, gestational hypertension and diabetes, parity, time of first antenatal visit to a healthcare provider), details about the delivery (type of delivery) and infant factors (birth weight, Apgar score). Air pollution data included information on particulate matter (PM10, PM2.5; 24-hour averages), nitrogen dioxide (NO2; 1-hour average), ozone (O3; 1-hour average) and carbon monoxide (CO; 1-hour average). Exposure periods were defined as 30 days and 90 days prior to delivery and 30 days and 90 days after the last menstrual period. Exposures were averaged across all air monitoring stations in metropolitan Sydney. Gestation was analysed as a categorical variable (< 37 weeks and >37 weeks) using logistic regression.
Results: Over the three year period there were 122,877 singleton births to mothers who did not have gestational hypertension and diabetes. 4.7% (n = 5831) of these births were preterm (< 37 weeks at birth). Median air pollutant concentrations were: PM10 24-h average = 15.7mg/m3, PM2.5 24-h average = 8.4mg/m3, NO2 1-h maximum = 23.0ppb, O3 1-h maximum = 27.7ppb and CO 1-h maximum = 1.2ppm. There was no effect of particulates or gaseous pollutants averaged over the month or three months prior to delivery on gestation. Particulates, NO2 and CO exposure in the first one and three months of pregnancy was associated with a lower risk for prematurity, whereas ozone exposure in the first three months of pregnancy increased the risk of preterm delivery.
Conclusions: Preliminary analyses suggest that in Sydney, Australia we were not able to demonstrate consistent adverse effects of ambient air pollution on preterm delivery. Exposure to ambient ozone in the first trimester was associated with an increased risk of preterm deliveries. However, as this was the only significant adverse finding among the many tests done, we advise caution in the interpretation of the results.
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