title: Variability in urinary phthalate metabolite levels across pregnancy and sensitive windows of exposure for the risk of preterm birth.
abstract: BACKGROUND
  Preterm birth is a significant public health problem, affecting over 1 in 10 live births and contributing largely to infant mortality and morbidity. Everyday exposure to environmental chemicals such as phthalates could contribute to prematurity, and may be modifiable. In the present study we examine variability in phthalate exposure across gestation and identify windows of susceptibility for the relationship with preterm birth.
  
  
  METHODS
  Women were recruited early in pregnancy as part of a prospective, longitudinal birth cohort at the Brigham and Women's Hospital in Boston, Massachusetts. Urine samples were collected at up to 4 time points during gestation for phthalate measurement, and birth outcomes were recorded at delivery. From this population we selected all 130 cases of preterm birth, defined as delivery before 37 weeks of completed gestation, as well as 352 random controls.
  
  
  RESULTS
  Urinary phthalate metabolite levels were moderately variable over pregnancy, but levels measured at multiple time points were associated with increased odds of preterm birth. Adjusted odds ratios (aOR) for spontaneous preterm birth were strongest in association with phthalate metabolite concentrations measured at the beginning of the third trimester (aOR for summed di-2-ethylhexyl phthalate metabolites [∑DEHP]=1.33, 95% confidence interval [CI]=1.02, 1.73). Odds ratios for placental preterm birth, defined as delivery with presentation of preeclampsia or intrauterine growth restriction, were slightly elevated in the first trimester for DEHP metabolites (aOR for ∑DEHP=1.33, 95% CI=0.99, 1.78).
  
  
  CONCLUSIONS
  Pregnant women with exposure to phthalates both early and late in pregnancy are at an increased risk of delivering preterm, but mechanisms may differ based on etiology.
authors.affiliation: Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI, United States.
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Ferguson
authors.affiliation: Division of Maternal-Fetal Medicine, Brigham and Women's Hospital, Boston, MA, United States; Harvard Medical School, Boston, MA, United States.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: McElrath
authors.affiliation: Department of Biostatistics, University of Michigan School of Public Health, Ann Arbor, MI, United States.
authors.forename: Yi-An
authors.initials: YA
authors.lastname: Ko
authors.affiliation: Department of Biostatistics, University of Michigan School of Public Health, Ann Arbor, MI, United States.
authors.forename: Bhramar
authors.initials: B
authors.lastname: Mukherjee
authors.affiliation: Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI, United States. Electronic address: meekerj@umich.edu.
authors.forename: John D
authors.initials: JD
authors.lastname: Meeker
mesh_terms: D000328:Adult; D001900:Boston / Q000453:epidemiology; D004051:Diethylhexyl Phthalate / Q000652:urine; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D018811:Maternal Exposure; D010795:Phthalic Acids / Q000378:metabolism / Q000633:toxicity* / Q000652:urine*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000652:urine; D037841:Pregnant People; D047928:Premature Birth / Q000139:chemically induced* / Q000453:epidemiology / Q000652:urine; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D010795:Phthalic Acids; C032279:phthalic acid; D004051:Diethylhexyl Phthalate
keywords: Longitudinal; Phthalate; Pregnancy; Repeated measures; Reproduction