title: Associations between Repeated Measures of Maternal Urinary Phthalate Metabolites and Thyroid Hormone Parameters during Pregnancy.
abstract: BACKGROUND
  Maintaining thyroid homeostasis during pregnancy is essential for normal fetal growth and development. Growing evidence suggests that phthalates interfere with normal thyroid function. Few human studies have investigated the degree to which phthalates may affect thyroid hormone levels in particularly susceptible populations such as pregnant women.
  
  
  OBJECTIVE
  We examined the associations between repeated measures of urinary phthalate metabolites and plasma thyroid hormone levels in samples collected at up to four time points per subject in pregnancy. Additionally, we investigated the potential windows of susceptibility to thyroid hormone disturbances related to study visit of sample collection.
  
  
  METHODS
  Data were obtained from pregnant women (n = 439) participating in a nested case-control study of preterm birth with 116 cases and 323 controls. We measured 9 phthalate metabolite concentrations in urine samples collected at up to four study visits per subject during pregnancy (median = 10, 18, 26, and 35 weeks of gestation, respectively). We also measured a panel of thyroid function markers in plasma collected at the same four time points per subject during pregnancy.
  
  
  RESULTS
  Although our results were generally null, in repeated measures analyses we observed that phthalate metabolites were largely inversely associated with thyrotropin and positively associated with free and total thyroid hormones. Cross-sectional analyses by study visit revealed that the magnitude and/or direction of these relationships varied by timing of exposure during gestation.
  
  
  CONCLUSIONS
  These results support previous reports showing the potential for environmental phthalate exposure to alter circulating levels of thyroid hormones in pregnant women. Citation: Johns LE, Ferguson KK, McElrath TF, Mukherjee B, Meeker JD. 2016. Associations between repeated measures of maternal urinary phthalate metabolites and thyroid hormone parameters during pregnancy. Environ Health Perspect 124:1808-1815; http://dx.doi.org/10.1289/EHP170.
authors.affiliation: Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, Michigan, USA.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Johns
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Ferguson
authors.forename: Thomas F
authors.initials: TF
authors.lastname: McElrath
authors.forename: Bhramar
authors.initials: B
authors.lastname: Mukherjee
authors.forename: John D
authors.initials: JD
authors.lastname: Meeker
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D047109:Fetal Development; D006706:Homeostasis; D006801:Humans; D016014:Linear Models; D010795:Phthalic Acids / Q000378:metabolism / Q000652:urine*; D011247:Pregnancy; D013963:Thyroid Hormones / Q000097:blood*
chemical_list: D010795:Phthalic Acids; D013963:Thyroid Hormones; C032279:phthalic acid