Air Pollution and Stillbirth: A Population-Based Case-Control Study in Taiwan

BACKGROUND: There is limited evidence suggesting that prenatal exposure to ambient air pollutants may increase the risk of stillbirth, but previous epidemiological studies have not elaborated the most susceptible gestational period for the effects of air pollution exposure on stillbirth. OBJECTIVES: We estimated associations between exposure to ambient air pollutants and stillbirth, with special reference to the assessment of gestational periods when the fetus is most susceptible. METHODS: We conducted a population-based case-control study in Taiwan. The case group consisted of 9,325 stillbirths, and the control group included 93,250 births randomly selected from 1,510,064 Taiwanese singleton newborns in 2001-2007. Adjusted logistic regression models were used to estimate odds ratios (ORs) per 10-ppb change for ozone and nitrogen dioxide, 1-ppb change for sulfur dioxide (SO(2)), 10-mu g/m(3) change for particulate matter with aerodynamic diameter <= 10 mu m (PM(10)), and 100-ppb change for carbon monoxide during different gestational periods and according to term or preterm (< 37 weeks) birth status. RESULTS: Stillbirth increased in association with a 1-ppb increase in first-trimester SO(2) [adjusted OR = 1.02; 95% confidence interval (CI), 1.00-1.04], particularly among preterm births (adjusted OR = 1.04; 95% CI, 1.01-1.07). Stillbirth was also associated with a 10-mu g/m(3) increase in PM(10) during the first (adjusted OR = 1.02; 95% CI, 1.00-1.05) and second (adjusted OR = 1.02; 95% CI, 1.00-1.04) month of gestation, and, as with SO(2), associations appeared to be restricted to preterm births (first-trimester adjusted OR = 1.03; 95% CI, 1.00-1.07). CONCLUSION: The study provides evidence that exposure to outdoor air SO(2) and PM(10) may increase the risk of stillbirth, especially among preterm births, and that the most susceptible time periods for exposure are during the first trimester of gestation.