What are the common types of thyroid disease in postpartum women with hypothyroidism?

Common Types of Thyroid Disease in Postpartum Women with Hypothyroidism

Postpartum thyroiditis (PPT) is the most common thyroid disorder in postpartum women with hypothyroidism, affecting 5-10% of women within the first year after delivery, with Hashimoto's thyroiditis being the most frequent underlying cause in industrialized nations. 1

Postpartum Thyroiditis (PPT)

Prevalence and Risk Factors

• Affects 5-10% of women in the first postpartum year 1
• Higher prevalence (up to 25%) in women with:
  • Type 1 diabetes (three-fold increase in risk) 2
  • Personal or family history of thyroid disease 1
  • Preexisting autoimmune disorders 1
• 70% risk of recurrence in subsequent pregnancies 1, 3

Clinical Patterns

PPT typically follows one of these patterns:

1. Classic biphasic pattern (22% of cases): Transient hyperthyroidism followed by transient hypothyroidism 4
2. Isolated hypothyroidism (48% of cases): Most common presentation 4
3. Isolated thyrotoxicosis (30% of cases): Hyperthyroid phase only 4

Underlying Causes in Postpartum Women with Hypothyroidism

1. Hashimoto's thyroiditis (chronic autoimmune thyroiditis): Most common cause in industrialized nations 5

   • Women with euthyroid Hashimoto's have higher risk (68.1%) of developing PPT compared to those with treated hypothyroid Hashimoto's (18.4%) 6
   • First-trimester euthyroidism is associated with nearly 4-fold higher risk of PPT 6

2. Other causes of hypothyroidism in postpartum women 5:

   • Subacute thyroiditis
   • History of radioactive iodine therapy
   • Previous thyroidectomy
   • Iodine deficiency (most common cause worldwide)

Clinical Presentation and Diagnosis

Hyperthyroid Phase (Typically 1-4 months postpartum) 7

• Palpitations, heat intolerance, anxiety, weight loss 1
• Differentiate from postpartum Graves' disease:
  • PPT: Occurs 1-4 months postpartum, negative TRAb, normal thyroid blood flow 7
  • Graves': Occurs 4-12 months postpartum, positive TRAb, increased thyroid blood flow 7

Hypothyroid Phase (Typically peaks around 19 weeks postpartum) 3

• Fatigue (most common symptom) 3, 4
• Cold intolerance, dry skin, impaired memory, aches and pains 3, 4
• Weight gain, intellectual slowness, constipation 5

Laboratory Testing

• TSH, Free T4 (FT4) or Free T4 Index (FTI) 1
• Anti-thyroid peroxidase (anti-TPO) antibodies to confirm autoimmune etiology 1
• Consider Free T3 if clinical suspicion is high but TSH and FT4 are incongruent 1

Long-term Outcomes

• Approximately 25-30% of women with PPT develop permanent hypothyroidism within 3 years 3
• Long-term studies show up to 50% develop permanent hypothyroidism within 7-9 years 3
• Risk factors for permanent hypothyroidism:
  • High TSH levels during hypothyroid phase 1
  • High anti-TPO antibody levels 1

Management Considerations

Hyperthyroid Phase

• Beta-blockers (e.g., propranolol) for symptomatic relief 1
• Antithyroid medications (propylthiouracil, methimazole) are NOT indicated as PPT is destructive thyroiditis rather than increased hormone production 1

Hypothyroid Phase

• Levothyroxine therapy recommended for:
  • Symptomatic patients with TSH 4-10 mU/L
  • All patients with TSH >10 mU/L
  • Starting dose: approximately 1.6 mcg/kg/day 1

Follow-up

• Monitor thyroid function every 2-3 weeks during active disease to detect transition between phases 1
• Annual thyroid function testing for women with history of PPT 1
• Women with PPT should be educated about the high risk of recurrence in future pregnancies 1