Exposure to Disinfection By-products, Fetal Growth, and Prematurity A Systematic Review and Meta-analysis

Background: Exposure to total trihalomethanes in drinking water has been associated with several adverse birth outcomes relating to fetal growth and prematurity. Methods: We carried out a systematic review and meta-analysis of epidemiologic studies featuring original peer-reviewed data on the association of total trihalomethane exposure and health outcomes related to fetal growth and prematurity. Results: A comprehensive literature search yielded 37 studies, 15 of which were selected for the extraction of relative risks relating adverse birth outcomes to trihalomethane exposure. Sufficient data were available for meta-analyses to be carried out for 4 adverse birth outcomes: low birth weight (LBW), term low birth weight (term LBW), preterm delivery, and small for gestational age (SGA) (including intra uterine growth retardation). We found little or no evidence for associations between third trimester trihalomethane exposure and LBW (odds ratio per 10 mu g total trihalomethane/L = 1.00 [95% confidence interval = 0.97-1.03]), term LBW (1.03 [0.93-1.15]), or preterm delivery (0.99 [0.98-1.00]), but some evidence for SGA (1.01 [1.00-1.02]). Conclusions: There was little or no evidence for associations between total trihalomethane concentration and adverse birth outcomes relating to fetal growth and prematurity, with the possible exception of SGA. We discuss these findings and the uncertainties-relating particularly to exposure-that may have affected them.