ORIGINAL ARTICLE

Effect of trihalomethane exposure on fetal development

J M Wright, J Schwartz, D W Dockery

Environmental Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA

Correspondence to:
Correspondence to:
Dr J M Wright, US Environnmental Protection Agency, National Center for Environmental Assessment, 26 West Martin Luther King Jr Drive (MS-190), Cincinnati, OH 45268, USA;
wright.michael{at}epa.gov

Aims: To examine the effect of trimester specific and pregnancy average total trihalomethane (TTHM) exposure on infant birth weight, low birth weight, and intrauterine growth retardation in term births, as well as gestational age and preterm delivery in all births.

Methods: Cross sectional analysis of 56 513 singleton infants born to residents of Massachusetts during 1990. City specific aggregate data were used to estimate maternal exposure to TTHM concentration; individual maternal information was used to adjust for confounding.

Results: Increased pregnancy average and second trimester TTHM exposure were associated with small for gestational age and reductions in birth weight after adjusting for potential confounding variables. Compared to 60 µg/l, pregnancy average TTHM exposure over 80 µg/l was associated with a 32 g reduction in birth weight. There was a 23 g reduction in birth weight in infants born to mothers exposed to greater than 80 µg/l TTHM during the second trimester. For each 20 µg/l increase in TTHM, the estimated reduction in birth was 2.8 g for pregnancy average exposure and 2.6 g for second trimester exposure. An increased risk of small for gestational age births was found for pregnancy average (odds ratio (OR) 1.14; 95% CI 1.02 to 1.26) and second trimester (OR 1.13, 95% CI 1.03 to 1.24) TTHM levels greater than 80 µg/l. There was no evidence of an association between preterm delivery and increased TTHM levels, but there were slight increases in gestational duration associated with TTHM concentrations.

Conclusions: Maternal exposure to THMs may be associated with fetal growth retardation. Our findings are consistent with most previous work, although we generally found smaller effects of TTHMs on low birth weight and intrauterine growth retardation.

Keywords: trihalomethane; disinfection byproducts; drinking water; fetal development; small for gestational age; intrauterine growth retardation

Abbreviations: BDCM, bromodichloromethane; CHCl₃, chloroform; CI, confidence interval; DBP, disinfection byproducts; EPA, Environmental Protection Agency; IUGR, intrauterine growth retardation; LBW, low birth weight; MX, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone; ND, non-detectable; OR, odds ratio; SGA, small for gestational age; TTHM, total trihalomethane

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