Background: Trihalomethanes in drinking water have been associated with higher occurrence of small-for-gestational-age (SGA) births, although results have been inconsistent.
Method: We geocoded residential address for mother of live, singleton, term births to 33 water distribution systems in a large metropolitan area of New South Wales, Australia (314,982 births between 1998 and 2004) and classified births into <10th percentile and ≥10 percentile of weight for gestational age. Mean trihalomethane exposure was estimated by trimester and for the entire pregnancy based on monthly sampling in each of the 33 water distribution systems. We estimated the relative risk (RR) of SGA for exposure to trihalomethanes using log-binomial regression adjusting for confounding.
Results: SGA births increased with mother's third-trimester exposure to chloroform (RR=1.04 [95% confidence interval=1.02–1.06], across an interquartile range [IQR]=25 μg/L) and bromodichloromethane (1.02 [1.01–1.04], 5 μg/L). Larger associations were found for SGA less than third percentile. Smoking modified the effects of trihalomethane exposure, with generally larger associations in births to nonsmoking mother and weaker or protective associations in births to smoking mothers.
Conclusions: Mothers' exposures during pregnancy to total trihalomethane as well as to chloroform and bromodichloromethane were associated with SGA. These associations were modified by maternal smoking during pregnancy.
From the aUniversity Center for Rural Health - North Coast, Medical School, University of Sydney, Lismore, New South Wales, Australia; bSchool of Health and Human Sciences, Southern Cross University, Lismore, New South Wales, Australia; cNorth Coast Area Health Service, New South Wales, Australia; dCentre for Quantitative Medicine, Duke-NUS Graduate Medical School, Singapore, Singapore; and eSchool of Public Health and Community Medicine, University of New South Wales, Sydney, New South Wales, Australia.
Submitted 19 October 2011; accepted 30 August 2011.
Supported by the Australian Research Council Linkage Grant (LP0348628) and Network for Spatially Integrated Social Science. The authors reported no other financial interests related to this research.
Institution where this work was performed: Northern Rivers University Department of Rural Health, Medical School, University of Sydney, Lismore, NSW Australia.
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Correspondence: Richard J. Summerhayes, University Centre for Rural Health - North Coast, 61 Uralba St, Lismore NSW 2480 Australia. E-mail: email@example.com.