Abstract:
Background: Previous studies have provided evidence that prenatal exposure to low-level air pollution increases
the risk of preterm birth (PTB), but the findings of the effects of short-term exposure have been inconclusive.
Moreover, there is little knowledge on potential synergistic effects of different combinations of air pollutants.
Objectives: To assess independent and joint effects of prenatal exposure to air pollutants during the week prior to
the delivery on the risk of PTB.
Methods: The study population included 2568 members of the Espoo Cohort Study, living in the City of Espoo,
Finland, born between 1984 and 1990. We assessed individual-level prenatal exposure to ambient air pollutants
of interest based on maternal residential addresses, while taking into account their residential mobility. We used
both regional-to-city-scale dispersion modelling and land-use regression–based method to estimates the pollu-
tant concentrations. We contrasted the risk of PTB in the highest quartile (Q4) of exposure to the lower exposure
quartiles (Q1-Q3) during the specific periods of pregnancy. We applied Poisson regression analysis to estimate
the adjusted risk ratios (RRs) with their 95% confidence intervals (CI), adjusting for season of birth, maternal
age, sex of the baby, family's socioeconomic status, maternal smoking, and exposure to environmental tobacco
smoke during pregnancy, single parenthood, and exposure to other air pollutants (this in multi-pollutant
models).
Results: The risk of PTB was related to exposures to PM2.5, PM10 and NO2 during the week prior to the delivery
with adjusted RRs of 1.67 (95%CI: 1.14, 2.46), 1.60 (95% CI: 1.09, 2.34) and 1.65 (95% CI: 1.14, 2.37), from
three-pollutant models respectively. There were no significant joint effects for these different air pollutants
(during the week prior to the delivery).
Conclusion: Our results provide evidence that exposure to fairly low-level air pollution may trigger PTB, but
synergistic effects of different pollutants are not likely.
