title: Drinking water disinfection by-product exposure and duration of gestation.
abstract: BACKGROUND
  Recent studies suggest elevated exposure to drinking water disinfection by-products (DBPs) may be associated with decreased risk of preterm birth. We examined this association for exposure to total trihalomethanes (TTHMs), 5 haloacetic acids (HAA5), and total organic halides.
  
  
  METHODS
  Analysis included 2039 women in a prospective pregnancy study conducted from 2000 through 2004 in 3 study sites. Water samples were collected and analyzed for DBP concentrations. Participant data were collected through interviews, an early ultrasound, and birth records. We assessed the associations between DBPs and preterm birth (<37-weeks' gestation) using log-binomial regression. Discrete-time hazard analysis was used to model the conditional odds of delivery each week in relation to DBP exposure.
  
  
  RESULTS
  Average second trimester DBP levels were associated with lower risk of preterm birth. Adjusted risk ratios for TTHM levels of 33.1-55.0, 55.1-66.3, 66.4-74.8, and 74.9-108.8 microg/L versus 2.2-4.6 microg/L were 0.8 (95% confidence intervals = 0.5-1.3), 0.9 (0.6-1.4), 0.7 (0.4-1.1), and 0.5 (0.3-0.9), respectively. Risk ratios for HAA5 levels of 17.9-22.0, 22.1-31.5, 31.6-40.4, and 40.5-52.8 microg/L versus 0-0.9 microg/L were 1.1 (0.8-1.7), 0.8 (0.5-1.2), 0.5 (0.3-0.8), and 0.7 (0.4-1.1), respectively. The conditional odds of delivery each week were decreased for the highest TTHM and HAA5 exposure groups versus the low exposure group for gestational weeks 33-40.
  
  
  CONCLUSIONS
  The probability of preterm birth was not increased with high DBP exposure.
authors.affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. dilworthch@niehs.nih.gov
authors.forename: Caroline S
authors.initials: CS
authors.lastname: Hoffman
authors.forename: Pauline
authors.initials: P
authors.lastname: Mendola
authors.forename: David A
authors.initials: DA
authors.lastname: Savitz
authors.forename: Amy H
authors.initials: AH
authors.lastname: Herring
authors.forename: Dana
authors.initials: D
authors.lastname: Loomis
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Hartmann
authors.forename: Philip C
authors.initials: PC
authors.lastname: Singer
authors.forename: Howard S
authors.initials: HS
authors.lastname: Weinberg
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Olshan
mesh_terms: D000328:Adult; D005260:Female; D047109:Fetal Development / Q000187:drug effects*; D005865:Gestational Age; D006801:Humans; D006846:Hydrocarbons, Halogenated / Q000032:analysis / Q000494:pharmacology*; D007231:Infant, Newborn; D011247:Pregnancy; D011446:Prospective Studies; D018508:Water Purification / Q000379:methods; D014881:Water Supply / Q000032:analysis
chemical_list: D006846:Hydrocarbons, Halogenated