The short term effects of exposure to aeroallergens during pregnancy on the risk of preterm birth
METHODS: A total of 33,126 preterm births which occurred in 6 large cities in the province of Ontario, Canada from 2005 to 2011 were identified from a provincial birth registry in order to conduct a time series study. Daily concentrations of total pollen and spore counts were obtained from fixed site monitoring stations in each city. Poisson regression models with distributed lag non-linear models were fitted for each city investigating the short term exposure during pregnancy in the population weighted average interquartile range (IQR) increase in total pollen and spore counts on the risk of preterm birth using the daily counts of premature births as the outcome measurement. Models were adjusted for outdoor air pollutants (NO2, O3), long term trends, seasonality, day of the week, and weather conditions. The city-specific estimates were pooled into a multivariate meta-analytical model.
RESULTS: An 8% (RR = 1.08; CI: 1.01 – 1.15) increased risk of preterm birth was observed for an IQR increase in ambient spore concentrations over a cumulative period of exposure of 6 days. Results also showed higher effect estimates among pregnant women who smoked during pregnancy. No effects were observed for exposure to an IQR increase in pollen concentrations (RR = 1.00; CI: 0.99 – 1.01).
CONCLUSIONS: This study is the first to investigate the impacts of aeroallergens on an adverse birth outcome which is associated with long term health consequences. This evidence has implications for pregnant women in terms of reducing their risks associated with the impacts of climate change.