title: Estimated effects of disinfection by-products on preterm birth in a population served by a single water utility.
abstract: OBJECTIVE
  We evaluated the association between drinking-water disinfection by-products and preterm births using improved exposure assessment and more appropriate analysis methods than used in prior studies.
  
  
  METHODS
  During 1999-2001, vital record data were obtained for a large, racially diverse population residing in 27 Massachusetts communities that received drinking water from a single public utility. This water system was monitored weekly for total trihalomethanes (TTHM), and it maintained geographically stable total TTHM levels system-wide during the study period. We employed proportional hazards regression to examine the effects of trimester-specific and shorter-term peak exposures to TTHM in drinking water late in pregnancy on preterm births in 37,498 singletons.
  
  
  RESULTS
  For all women, our data suggested no more than a small increase, if any, in risk for delivering a preterm baby when exposed to > or = 60 microg/L TTHM during the 4 weeks before birth [hazard ratio (HR) = 1.13; 95% confidence interval (CI), 0.95-1.35]. However, women who depended on a governmental source of payment for prenatal care were at increased risk when exposed at such levels late in gestation (HR = 1.39; 95% CI, 1.06-1.81). In contrast, exposure to high levels of TTHM during the second trimester and high exposure throughout pregnancy resulted in a 15-18% reduction in risk for preterm delivery in our population.
  
  
  CONCLUSIONS
  This finding confirms previous reports of a negative association during the second trimester. Our data also suggested a possible positive association with shorter-term third-trimester TTHM exposure in mothers of lower socioeconomic status.
authors: Environmental Science and Engineering Program, Department of Environmental Health Sciences, School of Public Health, University of California, Los Angeles, California, USA. myta_3@yahoo.com
authors: Chad
authors: C
authors: Lewis
authors: Irwin H
authors: IH
authors: Suffet
authors: Katherine
authors: K
authors: Hoggatt
authors: Beate
authors: B
authors: Ritz
mesh_terms: D004202:Disinfectants / Q000032:analysis / Q000633:toxicity*; D004203:Disinfection; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008404:Massachusetts; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D047928:Premature Birth / Q000453:epidemiology*; D018570:Risk Assessment; D012307:Risk Factors; D022882:Trihalomethanes / Q000032:analysis / Q000633:toxicity*; D018508:Water Purification
chemical_list: D004202:Disinfectants; D022882:Trihalomethanes