Low urinary iodine postpartum is associated with hypothyroid postpartum thyroid dysfunction and predicts long-term hypothyroidism

Clin Endocrinol (Oxf). 2011 May;74(5):631-5. doi: 10.1111/j.1365-2265.2011.03978.x.


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.

Design: Case-control with follow-up.

Patients: A total of 149 women at 6 months postpartum (74 PPTD, 75 controls) with 98 (46 PPTD, 52 controls) followed up at 12 years.

Measurements: 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.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Case-Control Studies
  • Female
  • Humans
  • Hypothyroidism / epidemiology
  • Hypothyroidism / urine*
  • Iodine / metabolism
  • Iodine / urine*
  • Longitudinal Studies
  • Postpartum Period*
  • Predictive Value of Tests*
  • Puerperal Disorders* / epidemiology
  • Thyroid Diseases
  • Western Australia


  • Iodine