title: Low urinary iodine postpartum is associated with hypothyroid postpartum thyroid dysfunction and predicts long-term hypothyroidism.
abstract: BACKGROUND
  Postpartum thyroid dysfunction (PPTD) is characterized by an early hyperthyroid phase followed, with peak prevalence at 6 months, by a hypothyroid phase which carries a risk of long-term hypothyroidism. Iodine has a major effect on thyroid function. Western Australia has previously been shown to be iodine replete.
  
  
  OBJECTIVE
  To examine the iodine status of women with and without PPTD and the relationship of iodine status postpartum with long-term hypothyroidism.
  
  
  METHODS
  Case-control with follow-up.
  
  
  METHODS
  A total of 149 women at 6 months postpartum (74 PPTD, 75 controls) with 98 (46 PPTD, 52 controls) followed up at 12 years.
  
  
  METHODS
  Urinary iodine concentration (UIC) and thyroid function at 6 months postpartum; thyroid function at 12-year follow-up.
  
  
  RESULTS
  At 6 months postpartum, median UIC (quartiles) for observed TSH ranges were: for TSH < 0·4 mU/l 130·0 μg/l (82·0, 170·0); for TSH 0·4-4·0 mU/l 123·0 μg/l (80·5, 168·0); for TSH > 4·0 mU/l 85·0 μg/l (40·0, 141·5), P = 0·018. The odds ratio (OR) of hypothyroid PPTD with each unit of decreasing log iodine was 2·54, (95%CI: 1·47, 4·35), and with UIC < 50 μg/l, OR 4·22, (95%CI: 1·54, 11·55). In the long term, decreased log UIC significantly predicted hypothyroidism at 12-year follow-up (P = 0·002); as did UIC < 100 μg/l (P = 0·03) and UIC < 50 μg/l (P = 0·02). The association was independent of antibody status.
  
  
  CONCLUSIONS
  Low UIC measured at 6 months postpartum is associated with hypothyroid PPTD and independently predicts long-term hypothyroidism. We believe that it results from more severe preceding destructive thyroiditis, with discharge of thyroidal iodine, and thereby predicts a greater risk of long-term hypothyroidism.
authors.affiliation: Keogh Institute for Medical Research, Nedlands, Western Australia, Australia. bstuckey@cyllene.uwa.edu.au
authors.forename: B G A
authors.initials: BG
authors.lastname: Stuckey
authors.forename: G N
authors.initials: GN
authors.lastname: Kent
authors.forename: J R
authors.initials: JR
authors.lastname: Allen
authors.forename: L C
authors.initials: LC
authors.lastname: Ward
authors.forename: S J
authors.initials: SJ
authors.lastname: Brown
authors.forename: J P
authors.initials: JP
authors.lastname: Walsh
mesh_terms: D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000453:epidemiology / Q000652:urine*; D007455:Iodine / Q000378:metabolism / Q000652:urine*; D008137:Longitudinal Studies; D049590:Postpartum Period; D011237:Predictive Value of Tests; D011644:Puerperal Disorders / Q000453:epidemiology; D013959:Thyroid Diseases; D014904:Western Australia
chemical_list: D007455:Iodine