Association Between Maternal Exposure to Elevated Concentration of Trihalomethanes in Drinking Water During Pregnancy and Adverse Birth Outcomes in Queensland, Australia: A Population-Based Data Linkage Study

Epidemiological evidence between exposure to trihalomethanes (THMs) and adverse birth outcomes remains inconsistent. We examined the associations between maternal exposure to elevated THM concentration in drinking water during pregnancy and adverse birth outcomes, including preterm birth (PTB), low birthweight (LBW), and small-for-gestational age (SGA). We analysed population-based data of 134,966 singleton livebirths recorded across 25 local government areas (LGAs) between 2009 and 2020 using the Queensland Perinatal Data Collection, water quality monitoring data, meteorological data, and Australian Bureau of Statistics records. Maternal exposure to elevated THM exceeding thresholds of ≥ 250, ≥100, ≥ 80, and ≥ 70 µg/L was defined using monthly total THM concentrations. We applied Generalized Estimating Equation models to examine exposure-outcome associations. Overall, 6.8% of babies were born preterm, 5.0% LBW, and 9.2% SGA, with marked geographic disparities across background characteristics. Temporal analyses revealed an increase in LBW prevalence from 3.7% to 5.2% (average annual rate of change 1.6%). Lower odds of SGA were associated with maternal exposure to elevated THM concentrations at ≥ 100 µg/L (Adjusted Odds Ratio, AOR = 0.91, 95% CI [0.88–0.95]) and at ≥ 80 µg/L (0.93, [0.88–0.97]). Across individual disinfection by-products, bromodichloromethane exceedance at ≥ 250 µg/L was associated with higher odds of PTB (1.07, [1.01,1.13]), and bromoform exceedance at ≥ 70 µg/L was associated with higher odds of LBW (1.22, [1.01,1.48]). The disparities in adverse birth outcomes warrant identifying regional factors to inform targeted health interventions. Continued research employing improved study design and more accurate exposure measurement is needed to synthesize conclusive evidence and clarify causal relationships to inform decision-making.