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

We aimed to provide quantitative estimates of exposure-response relationships between total trihalomethanes in drinking water and several adverse birth outcomes relating to fetal growth and prematurity, suitable for use in assessments of attributable burden of disease. We carried out a systematic review and meta-analysis of epidemiological studies featuring original peer-reviewed data on the association of total trihalomethane (TTHM) exposure and health outcomes related to fetal growth and prematurity. A comprehensive literature search yielded 37 studies for consideration, 15 of which were selected for the extraction of relative risks relating adverse birth outcomes to TTHM exposure. Sufficient data were available for meta-analyses to be carried out for four adverse birth outcomes: low birth weight (LBW), term low birth weight (TLBW), preterm delivery (PTD) and small for gestational age (SGA) (including intra uterine growth retardation (IUGR)). We found little or no evidence for associations between third trimester TTHM exposure and LBW (OR per 10µg TTHM/L = 0.9999 95% CI 0.9735, 1.0270), TLBW (OR per 10µg TTHM/L = 1.0337 95% CI 0.9272, 1.1525) or PTD (OR per 10µg TTHM/L = 0.9896 95% CI 0.9781, 1.0013). We found evidence for an association with SGA (OR per 10µg TTHM/L = 1.0100 95% CI 1.0006, 1.0194). We found little or no evidence for associations between TTHM concentration and most adverse birth outcomes relating to fetal growth and prematurity. We did find evidence for an association between TTHM concentration and SGA. We discuss these findings and the uncertainties—relating particularly to exposure which may have affected them.