Trihalomethane Exposure at Pregnancy, Birth Weight, and Duration of Gestation: Results From a Cohort Study in Spain

Abstract

S-01A3-4 Background/Aims: Exposure to disinfection byproducts during pregnancy has been associated with reduced birth weight and altered duration of gestation but evidence remains inconclusive. We assessed exposure to trihalomethanes (THMs) during pregnancy through ingestion, showering, bathing, and swimming in pools and evaluated the association with birth weight, small for gestational age (SGA), low birth weight (LBW), and duration of gestation. Methods: A mother-child cohort study was set up in Asturias, Gipúzkoa, Sabadell, Valencia, and Granada (INMA project). Study population was recruited at week 12 of gestation and followed up to delivery. A personal interview at week 32 requested water use: source of drinking water, showering, bathing, and swimming in pools. Trihalomethane level was ascertained through sampling campaigns (834 measurements) and regulatory data (264 measurements) during the pregnancy period. Chloroform, bromodichloromethane, dibromochloromethane, bromoform, and total THM were modeled for each region, predicting monthly level over pregnancy. Modeled residential THM was combined with personal water use and uptake factors to estimate THM uptakes. Outcomes were defined following standard definitions. Linear and logistic regressions adjusting for potential confounders were applied stratifying by area and all areas combined. Results: Total THM ranged from a median of 5.9 μg/L (Valencia) to 114.7 μg/L (Sabadell). A total of 2091 newborns were included, with 52% male, mean birthweight of 3267 g, 10.5% SGA, 5.1% LBW, and 3.8% preterm. All area combined estimated change of birth weight for a 10% increase in uptake was −0.46 g (−1.36, 0.45) for chloroform and 0.18 g (−1.36, 1.71) for brominated THMs. A meta-analysis showed no heterogeneity of effects among areas. Chloroform uptake was not associated with SGA, slightly increased LBW risk, and moderately reduced the risk of preterm delivery. Conclusion: Despite the high THM levels in some areas, THM exposure was not associated with birthweight or SGA and was only slightly associated with LBW and preterm birth.