Postpartum thyroiditis

Did You Know?

• Women with type I diabetes mellitus have a threefold increase in the prevalence of postpartum thyroiditis than non-diabetic women in the same region.
• In Bangkok, Thailand the rate of postpartum thyroiditis is 1.1%, but in Brazil it is 13.3%.

Signs and symptoms

The initial hyperthyroid phase occurs transiently about two to six months postpartum, with symptoms such as irritability, nervousness, palpitations, and heat intolerance. These hormonal disturbances tend to be less intense than those of the hypothyroid phase, so the hyperthyroid phase may go undetected. The hypothyroid phase can occur anytime within three to twelve months postpartum, bringing low energy, poor memory, impaired concentration, dry skin, cold intolerance, and general aches and pains. After one year, euthyroid function usually resumes; cases with hypothyroid symptoms beyond one year are not considered postpartum thyroiditis. Women with thyroid antibodies may have an increased risk of symptoms associated with postpartum depression.

Cause

During pregnancy, immunologic suppression induces tolerance to the fetus; after delivery, the immune system rebounds, causing levels of thyroid antibodies to rise in susceptible women. Immunohistological features include antibodies to thyroglobulin (TgAb) and thyroid peroxidase (TPOAb), an increase in TPOAb subclasses IgG1-IgG3, lymphocyte infiltration and follicle formation within the thyroid gland (Hashimoto's thyroiditis), an increased CD4:CD8 ratio, and TSH-receptor antibodies (TSH-R Abs).

Diagnosis

Doctors often miss postpartum thyroiditis because they are not familiar with it, the symptoms are mild, or they blame them on the stress of a new baby. Testing starts with a TSH level. A low TSH might mean the hyperthyroid phase, but more tests are needed to check for Graves' disease. If TSH is normal but symptoms continue, the patient may be shifting phases; a repeat test in four to six weeks is needed. A high TSH at that point could signal the hypothyroid phase.

Treatment

For most women, the hyperthyroid phase is mild or asymptomatic and usually requires no intervention; if symptomatic, a short course of beta-blockers is effective. Treatment for the hypothyroid phase is more complex: women with symptoms or a very high TSH level, or both, are typically prescribed levothyroxine. Asymptomatic women with slightly elevated TSH who plan subsequent pregnancies should consider treatment until completion of the family to avoid possible developmental complications; otherwise, treatment may be discontinued after one year postpartum.