What is the best management plan for a pregnant woman with Hashimoto's thyroiditis and elevated Thyroid-Stimulating Hormone (TSH) levels, currently taking Armour Thyroid (levothyroxine), to ensure adequate fetal thyroid hormone delivery?

Management of Hashimoto's Thyroiditis with Elevated TSH in Pregnancy

Immediately discontinue Armour Thyroid and switch to levothyroxine monotherapy at an appropriate dose, as T3-containing preparations like Armour Thyroid provide inadequate fetal thyroid hormone delivery and pose significant risk to fetal neurodevelopment. 1, 2

Critical Medication Change Required

• Levothyroxine (T4) monotherapy is the only acceptable treatment during pregnancy because T3 does not cross the placenta adequately to support fetal brain development 1, 2
• Armour Thyroid contains both T4 and T3, making it inappropriate for pregnancy as the T3 component provides no benefit to the fetus while the T4 dose may be insufficient 1, 2
• Untreated or inadequately treated maternal hypothyroidism increases risk of preeclampsia, low birth weight, and permanent neurodevelopmental deficits in the child 1, 3

SOAP Note

Subjective: Pregnant patient with known Hashimoto's thyroiditis currently taking Armour Thyroid presents with elevated TSH. Patient reports [insert relevant symptoms: fatigue, cold intolerance, weight changes, etc.]. Currently [X] weeks pregnant.

Objective:

• TSH: [elevated value] mIU/L (trimester-specific reference range needed)
• Free T4: [value if available]
• Anti-TPO antibodies: positive (confirming Hashimoto's thyroiditis)
• Current medication: Armour Thyroid [dose]

Assessment:

1. Inadequately controlled hypothyroidism secondary to Hashimoto's thyroiditis in pregnancy
2. Inappropriate thyroid hormone preparation for pregnancy (Armour Thyroid contains T3)
3. Risk for adverse pregnancy outcomes and fetal neurodevelopmental impairment if not corrected immediately

Plan:

Immediate Medication Management

• Discontinue Armour Thyroid immediately 1, 2
• Start levothyroxine monotherapy at appropriate dose based on pregnancy status 4, 5:
  • For new-onset hypothyroidism with TSH ≥10 mIU/L: 1.6 mcg/kg/day 5
  • For pre-existing hypothyroidism: increase pre-pregnancy levothyroxine dose by 25-50% immediately upon pregnancy confirmation 1, 5
  • If pre-pregnancy dose unknown, calculate based on 1.6 mcg/kg/day and adjust 5

Monitoring Protocol

• Check TSH and free T4 every 4 weeks until stable, then at minimum once per trimester 4, 5
• Target TSH within trimester-specific reference range, ideally <2.5 mIU/L in first trimester 1, 3
• Adjust levothyroxine dose by 12.5-25 mcg increments based on TSH results 5
• Levothyroxine requirements typically increase 25-50% during pregnancy in women with pre-existing hypothyroidism 1, 6

Patient Education

• Take levothyroxine on empty stomach, 30-60 minutes before breakfast for optimal absorption 1
• Separate levothyroxine from prenatal vitamins (especially iron and calcium) by at least 4 hours 1
• Explain that T3-containing preparations like Armour Thyroid do not provide adequate thyroid hormone to the developing fetus 1, 2
• Emphasize critical importance of thyroid hormone for fetal brain development, particularly in first and second trimesters 4, 2
• Discuss that inadequate treatment risks permanent neurodevelopmental deficits, low birth weight, and preeclampsia 1, 3
• Advise that levothyroxine dose will likely need adjustment throughout pregnancy and should return to pre-pregnancy levels immediately after delivery 5, 6

Referral to Reproductive Endocrinology

Refer to reproductive endocrinology/maternal-fetal medicine for:

• Co-management of thyroid disease throughout pregnancy given complexity of Hashimoto's thyroiditis in pregnancy 3
• Optimization of thyroid hormone levels for fetal neurodevelopment 3
• Monitoring for potential postpartum thyroiditis exacerbation, which occurs frequently in Hashimoto's patients 2, 6
• Assessment for other autoimmune conditions that may coexist with Hashimoto's thyroiditis 1

Prescription

Levothyroxine [calculated dose based on weight] mcg PO daily

• Take on empty stomach, 30-60 minutes before breakfast
• Do not take within 4 hours of iron, calcium, or antacids
• Dispense: 90-day supply
• Refills: 3

Follow-up

• Recheck TSH and free T4 in 4 weeks 5
• Continue monitoring every 4 weeks until stable, then each trimester 4, 5
• Plan for dose reduction to pre-pregnancy level immediately postpartum 5, 6
• Monitor TSH 4-8 weeks postpartum as >50% of Hashimoto's patients experience increased levothyroxine requirements postpartum compared to pre-pregnancy 6

Critical Pitfalls to Avoid

• Never continue T3-containing preparations during pregnancy as they provide inadequate fetal thyroid hormone delivery 1, 2
• Do not wait for symptoms to develop before checking TSH, as fetal harm can occur before maternal symptoms appear 1
• Avoid TSH targets >2.5 mIU/L in first trimester, as even subclinical hypothyroidism is associated with adverse pregnancy outcomes 1, 3
• Do not assume stable pre-pregnancy doses will suffice during pregnancy—most patients require 25-50% dose increases 1, 6
• Remember that postpartum thyroiditis exacerbation is common in Hashimoto's patients, requiring continued monitoring after delivery 2, 6