Description

• Postpartum thyroiditis (PPT) is an autoimmune-mediated destructive thyroiditis occurring within 1 year after delivery or spontaneous/induced abortion. It manifests as transient hyperthyroidism, transient hypothyroidism, or transient hyperthyroidism followed by transient hypothyroidism with subsequent recovery. Initial thyrotoxicosis can last 6 to 9 weeks (1,2).
• Euthyroid conditions are usually regained within 1 year. A small population may develop chronic hypothyroidism several years after recovery (3).
• Although PPT usually occurs 2 to 4 months postpartum, the condition may present during the peripartum period, especially with those with a previous history of PPT.
• Peripartum thyroiditis is very uncommon. Case studies have shown the condition to present in the late 1st trimester/early 2nd trimester. Of the recorded occurrences, patients affected had a history of PPT; also, those diagnosed with peripartum thyroiditis had a previous delivery or abortion within the last 18 months (4).

Epidemiology

Incidence

• PPT incidence varies greatly in different regions of the world. The lowest incidence of 1.1% is noted in Thailand and up to 21.1% in Canada (5). Generally, the incidence is approximately 5–9% (1).
• Incidence of peripartum thyroiditis is unmeasured because only a few isolated cases have been recorded.

Etiology and Pathophysiology

• Autoimmune inflammation of the thyroid caused by changes in humoral and cell-mediated immune response (1)
• Thyroid inflammation results in destruction of thyroid follicles releasing thyroglobulin causing excessive amounts of triiodothyronine and thyroxine, a hyperthyroid state (1).

Genetics

• Associated with HLA-B and HLA-D haplotypes (1)
• Likely affected by a variety of genetic and nongenetic factors in different geographic regions (1)
• Positive titers for thyroid peroxidase (TPO) antibodies are present in >50% of patient diagnosed with post and peripartum thyroiditis. Increasing maternal age has been linked to increasing frequency of TPO Ab.

Risk Factors

• Major:
  • Previous PPT; this increases subsequent risk by 70%.
  • Hypothyroidism antedating pregnancy (1,5)
  • History of other autoimmune disorders such as type 1 diabetes (5)
• Minor:
  • Iodine excess or deficiency
  • Smoking
  • Radiation exposure to head or neck region
  • Untreated chronic hepatitis C virus
  • Medications such as lithium, amiodarone, interferon-α, interleukin-2, and highly active antiretroviral therapy increase risk with positive TPO Ab titers.

General Prevention

• Several studies have linked vitamin D insufficiency/deficiency to increased risk for PPT (6).
• Due to low incidence and difficulty in predictability, there has been no established prevention strategies. It is best to minimize modifiable risk factors.

Commonly Associated Conditions

Graves disease, hyperthyroidism, subacute thyroiditis, simple goiter