Meta-Analysis of Small for Gestational Age Births and Disinfection Byproduct Exposures
Meta-analysis of Small for Gestational Age Births and Aggregate Disinfection By-product Exposures Background: Some epidemiological studies show associations between disinfection byproducts (DBPs) and adverse developmental outcomes. Objectives: We undertook a meta-analysis of epidemiological studies on maternal exposure to trihalomethanes (THMs) and haloacetic acids (HAAs) and risk of small for gestational age (SGA) birth. Methods: Forty-seven manuscripts, two reports and five theses were identified via a 2020 literature search. Eighteen study populations from 16 publications met the inclusion criteria and were systematically evaluated. Effect measures were pooled using random effects meta-analytic methods along with cumulative, sub-group and meta-regression analyses to examine between-study and DBP measure heterogeneity. Results: We detected a small increased risk for SGA with exposure to the sum of four (i.e., THM4) THMs (odds ratio (OR)=1.07; 95%CI: 1.03, 1.11), chloroform (OR=1.05; 95%CI: 1.01, 1.08), bromodichloromethane (OR=1.08; 95%CI: 1.05, 1.11) and the sum of the brominated THMs (OR=1.05; 95%CI: 1.02, 1.09). Larger ORs were detected for the sum of five haloacetic acids (OR=1.12; 95%CI: 1.01, 1.25), dichloroacetic acid (OR=1.25; 95%CI: 1.01, 1.41) and trichloroacetic acid (OR=1.21; 95%CI: 1.07, 1.37). We detected larger risks of SGA for several THMs among the prospective and case-control studies compared to retrospective cohorts and for the SGA3/5% (vs. SGA10%) percentile studies. The THM4 meta-regression showed associations between SGA and the total quality score based on categorical or continuous measures. For example, an OR of 1.03 (95%CI: 1.01, 1.06) was detected for each 10-point increase in the study quality score based on our systematic review. Conclusions: We detected a small increased risk of SGA based on 18 THM4 study populations that was comparable to a previous meta-analysis of eight THM4 study populations. We also found increased risks for other THMs and HAA measures not previously examined; these results were robust after accounting for outliers, publication bias, type of SGA classification, different exposure windows, and other factors.