What is the management of thyroid disorders in pregnancy?

Management of Thyroid Disorders in Pregnancy

The management of thyroid disorders in pregnancy requires prompt diagnosis and appropriate treatment to reduce maternal and fetal morbidity and mortality, with hypothyroidism treated with levothyroxine to normalize TSH levels and hyperthyroidism managed with thioamides, preferably propylthiouracil in the first trimester. 1, 2, 3

Diagnostic Approach

• Initial Testing: TSH is the recommended initial screening test for thyroid dysfunction in pregnant women with suspected thyroid disease 1
• Comprehensive Evaluation: Both TSH and Free T4 (FT4) or Free T4 Index (FTI) should be measured in pregnant women with suspected hyperthyroidism or hypothyroidism 1
• Targeted Screening: Universal screening is not recommended, but targeted screening is appropriate for high-risk women 4

Management of Hypothyroidism in Pregnancy

Diagnosis

• Most common causes: chronic autoimmune thyroiditis (Hashimoto's), previous thyroidectomy, radioactive iodine therapy, and iodine deficiency 5
• Clinical presentation: fatigue, muscle cramps, constipation, cold intolerance, hair loss, weight gain 5

Treatment

• Medication: Levothyroxine is the treatment of choice 1, 2
• Dosing:
  • Initial dose approximately 1.6 mcg/kg/day 5
  • Adjust dose every 4 weeks until TSH level is stable 1
• Target: TSH goal of <2.5 mIU/L 6
• Monitoring: Check TSH every trimester 1
• Postpartum: Return to pre-pregnancy dose immediately after delivery 2

Clinical Implications

• Untreated maternal hypothyroidism increases risk of:
  • Preeclampsia
  • Low birth weight
  • Spontaneous abortion
  • Preterm delivery
  • Adverse effects on fetal neurocognitive development 2, 6

Management of Hyperthyroidism in Pregnancy

Diagnosis

• Differentiate between:
  • Graves' disease (most common cause of true hyperthyroidism)
  • Gestational transient thyrotoxicosis (associated with hyperemesis gravidarum)
  • Postpartum thyroiditis 1, 5

Treatment for Graves' Disease

• First-line medication: Thioamides (propylthiouracil or methimazole) 1, 3
• First trimester: Propylthiouracil preferred due to lower risk of teratogenicity 3, 6
• Second and third trimesters: Consider switching to methimazole 3
• Dosing: Use lowest possible dose to maintain FT4 or FTI in high-normal range 1
• Monitoring: Measure FT4 or FTI every 2-4 weeks 1
• Symptom control: Beta-blockers (e.g., propranolol) can be used temporarily until thioamide therapy reduces thyroid hormone levels 1

Treatment for Gestational Transient Thyrotoxicosis

• Usually self-limiting and rarely requires treatment 1
• Supportive care and hydration are typically sufficient 5
• No routine thyroid testing unless other signs of hyperthyroidism are present 1

Important Precautions

• Radioactive iodine (I-131): Absolutely contraindicated during pregnancy 1
• Thyroidectomy: Reserved only for women who do not respond to thioamide therapy 1
• Medication side effects: Monitor for agranulocytosis (presents with sore throat and fever), hepatitis, vasculitis, and thrombocytopenia 1, 3

Postpartum Thyroid Management

Postpartum Thyroiditis (PPT)

• Affects 5-10% of women within first year after delivery 5
• Typically follows biphasic pattern (hyperthyroid phase followed by hypothyroid phase) 5
• Treatment:
  • Hyperthyroid phase: Beta-blockers for symptomatic relief 5
  • Hypothyroid phase: Levothyroxine for symptomatic patients or TSH >10 mIU/L 5
• Monitoring: Check thyroid function every 2-3 weeks to detect transition to hypothyroid phase 5
• Long-term follow-up: 20-40% develop permanent hypothyroidism; annual thyroid function testing recommended 5

Breastfeeding Considerations

• Propylthiouracil and methimazole are both considered safe during breastfeeding 1, 3
• Levothyroxine can be continued safely during breastfeeding 5, 2
• Women should not breastfeed for four months after treatment with I-131 1

Thyroid Storm in Pregnancy

Diagnosis

• Extreme hypermetabolic state with high risk of maternal heart failure 1
• Signs/symptoms: fever, tachycardia out of proportion to fever, altered mental status, vomiting, diarrhea, cardiac arrhythmia 1
• Often precipitated by surgery, infection, labor, or delivery 1

Treatment

• Requires immediate intervention - do not delay treatment awaiting test results 1
• Standard treatment includes:
  • Thioamide (propylthiouracil or methimazole)
  • Saturated solution of potassium iodide or sodium iodide
  • Beta-blockers
  • Supportive care 1

Key Pitfalls to Avoid

• Failing to differentiate between PPT and Graves' disease, leading to unnecessary treatment 5
• Overlooking transition from hyperthyroid to hypothyroid phase in PPT 5
• Not adjusting levothyroxine dosage during pregnancy (requirements often increase) 2
• Using radioactive iodine during pregnancy or breastfeeding 1
• Delaying treatment of thyroid storm 1