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Sharon K. Sagiv,¹ Pauline Mendola,² Dana Loomis,¹ Amy H. Herring,³ Lucas M. Neas,² David A. Savitz,¹ and Charles Poole¹

¹Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA; ²National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ³Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA

Abstract
Preterm delivery can lead to serious infant health outcomes, including death and lifelong disability. Small increases in preterm delivery risk in relation to spatial gradients of air pollution have been reported, but previous studies may have controlled inadequately for individual factors. Using a time-series analysis, which eliminates potential confounding by individual risk factors that do not change over short periods of time, we investigated the effect of ambient outdoor particulate matter with diameter ≤ 10 µm (PM₁₀) and sulfur dioxide on risk for preterm delivery. Daily counts of preterm births were obtained from birth records in four Pennsylvania counties from 1997 through 2001. We observed increased risk for preterm delivery with exposure to average PM₁₀ and SO₂ in the 6 weeks before birth [respectively, relative risk (RR) = 1.07 ; 95% confidence interval (CI) , 0.98-1.18 per 50 µg/m³ increase ; RR = 1.15 ; 95% CI, 1.00-1. 32 per 15 ppb increase], adjusting for long-term preterm delivery trends, co-pollutants, and offsetting by the number of gestations at risk. We also examined lags up to 7 days before the birth and found an acute effect of exposure to PM₁₀ 2 days and 5 days before birth (respectively, RR = 1.10 ; 95% CI, 1.00-1.21 ; RR = 1.07 ; 95% CI, 0.98-1.18) and SO₂ 3 days before birth (RR = 1.07 ; 95% CI, 0.99-1.15) , adjusting for covariates, including temperature, dew point temperature, and day of the week. The results from this time-series analysis, which provides evidence of an increase in preterm birth risk with exposure to PM₁₀ and SO₂, are consistent with prior investigations of spatial contrasts. Key words: air pollution, environmental epidemiology, particulate matter, pregnancy, preterm birth, sulfur dioxide. Environ Health Perspect 113:602-606 (2005) . doi:10.1289/ehp.7646 available via http://dx.doi.org/ [Online 2 February 2005]

Address correspondence to S. Sagiv, Channing Laboratory, 181 Longwood Ave., Boston, MA 02115 USA. Telephone: (617) 525-4210. Fax: (617) 525-2578. E-mail: sharon.sagiv@channing.harvard.edu

This work was supported by National Health and Environmental Effects Research Laboratory-Department of Environmental Sciences and Engineering Cooperative Training in Environmental Sciences Research, EPA CT826513. A.H.H. and C.P. were supported by National Institute of Environmental Health Sciences Center Grant P30ES10126.

This research has been supported in part by the U.S. Environmental Protection Agency. It has been subjected to review by the National Health and Environmental Effects Research Laboratory and approved for publication. Approval does not signify that the contents reflect the views of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

The authors declare they have no competing financial interests.

Received 7 October 2004 ; accepted 2 February 2005.