The Sixteenth Conference of the International Society for Environmental Epidemiology (ISEE): Abstracts
This study, in three water regions, is the largest yet conducted of the association between disinfection by-products in the public water supply, as measured by individual trihalomethanes (THMs), and stillbirth and birth weight prevalence.
Modelled estimates of quarterly individual THM concentrations in water zones by year, categorised as low (for chloroform, >20 μg/l; for bromodichloromethane (BDCM) and total brominated THMs (TBTHM), >6 μg/l), medium (for chloroform, 20–40 μg/l; for BDCM and TBTHM, 6–12 μg/l) or high (for chloroform, <40 μg/l; for BDCM and TBTHM, <12 μg/l), were linked to 1,015,298 routine birth and still birth records using maternal residence at time of birth through the use of Geographical Information Systems.
In one region, a trend of increasing prevalence of stillbirth and low and very low birth weight from low to medium to high chloroform exposure areas was observed — for example, with adjustment for potential confounders including maternal age and social deprivation, risks of stillbirth and low birth weight in high chloroform compared with low chloroform exposure areas were 1.15 (95% CI 1.01 to 1.32) and 1.17 (95% CI 1.13 to 1.22) respectively. There was no significant relation between chloroform and excess adverse birth outcomes in the other regions. In a meta-analysis across the three regions, small, but significant, excess risks were found in areas with high chloroform concentrations for both stillbirths (OR 1.12; 95% CI 1.02 to 1.23) and low birth weight (OR 1.10; 95% CI 1.07 to 1.13); no associations were found with very low birth weight. Concentrations of BDCM and TBTHMs did not show any significant association with risk of stillbirths, low and very low birth weight in all three regions separately and combined. Analysis of stillbirth risk associated with specific THMs was also conducted by cause-of-death sub-category.
These findings suggest a need to focus on specific individual (as opposed to total) THMs and/or other disinfection by-products in relation to stillbirth and low birth weight risk. This type of focused research, which is very under-developed at present, informs cross-study comparisons and helps to refine risk estimates in order to differentiate between possible causal and alternative (non-causal) explanations.