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

Article excerpt

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 (S[O.sub.2]), 10-pg/m3 change for particulate matter with aerodynamic diameter < 10 pm (P[M.sub.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 S[O.sub.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-pg/m3 increase in P[M.sub.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 S[O.sub.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 S[O.sub.2] and PMI0 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.

KEYWORDS: air pollution, particle, stillbirth, sulfur dioxide. Environ Health Perspect 119:1345-1349 (2011). http://ck.doi.org/10.1289/ehp.1003056 [Online 29 March 2011]

Epidemiologic studies since the 1990s have provided evidence that prenatal exposure to ambient air pollution may increase the risk of low birth weight and small for gestational age and preterm births (Lacasana et al. 2005; Maisonet et al. 2004; Ritz and Yu 1999; Ritz et al. 2007). There is limited evidence suggesting that prenatal exposure to ambient air pollutants may increase the risk of stillbirth, and previous studies have not identified which gestational periods are most susceptible to effects of air pollution on risks of stillbirth (Bobak and Leon 1999; Pearce et al. 2010; Pereira et al. 1998; Sakai 1984). In a Japanese ecological study, the risk for stillbirth was related to regional levels of nitrogen dioxide (N[O.sub.2]) and sulfur dioxide (S[O.sub.2]) (Sakai 1984). Another ecological study conducted in the Czech Republic reported an elevated, significant effect estimate of stillbirth for nitrogen oxides (N[O.sub.x]) but no association between S[O.sub.2] and suspended particulate matter (PM) (Bobak and Leon 1999). A time-series study in Brazil reported a statistically significant association between daily exposure to N[O.sub.x], S[O.sub.2], and carbon monoxide (CO) and the risk of stillbirth (Pereira et al. 1998). A recent study conducted in northern England found no association between black smoke air pollution during pregnancy and the risk of stillbirth (Pearce et al. 2010).

We conducted a nationwide population-based case-control study in Taiwan to assess the effects of ambient air pollution exposure during pregnancy on the risk of stillbirth, with special reference to the assessment gestational periods when the fetus is most susceptible. These susceptible time windows of exposure could elucidate possible mechanisms underlying the effects of ambient air pollution on the risk of stillbirth. …