Does taking levothyroxine (synthetic thyroid hormone) for postpartum thyroiditis affect the breastfed baby due to the medication?

Levothyroxine During Breastfeeding for Postpartum Thyroiditis

Levothyroxine use during lactation is safe and does not negatively affect breastfed infants. 1 Published studies report that while levothyroxine is present in human milk following oral administration, no adverse effects on breastfed infants have been reported.

Safety of Levothyroxine During Breastfeeding

Levothyroxine is considered compatible with breastfeeding for several important reasons:

• The FDA drug label explicitly states that "no adverse effects on the breastfed infant have been reported" when mothers take levothyroxine 1
• The drug label further notes that "adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply" 1
• The developmental and health benefits of breastfeeding outweigh any theoretical concerns about levothyroxine use during lactation 1

Importance of Treating Postpartum Thyroiditis

Postpartum thyroiditis requires appropriate management for optimal maternal and infant outcomes:

• Postpartum thyroiditis is diagnosed by new onset of abnormal TSH levels, abnormal FT4 levels, or both 2
• Whether treatment is needed depends on the severity of the abnormality and symptoms 2
• The risk of permanent hypothyroidism is greatest in women with the highest levels of TSH and antithyroid peroxidase antibodies 2
• Up to 56% of women who experience hypothyroid postpartum thyroiditis will develop permanent hypothyroidism, making proper treatment essential 3

Monitoring Recommendations

For women with postpartum thyroiditis taking levothyroxine:

• TSH and FT4 levels should be evaluated in women who develop postpartum symptoms of hypothyroidism 2
• Periodic thyroid function testing is recommended following recovery from postpartum thyroiditis due to the high lifetime risk of developing permanent hypothyroidism 4
• Serum TSH should be checked in cases of postpartum depression or difficulty lactating 4

Benefits of Breastfeeding While on Thyroid Medication

The 2020 American College of Rheumatology guidelines and other medical authorities strongly support breastfeeding while taking levothyroxine:

• Women should be encouraged to breastfeed if they desire and are able to do so 2
• Disease control should be maintained with lactation-compatible medications like levothyroxine 2
• The benefits of breastfeeding for both mother and infant are numerous and well-documented 2

Clinical Pearls and Pitfalls

1. Do not discontinue levothyroxine during breastfeeding - Untreated maternal hypothyroidism can lead to decreased milk production 1

2. Monitor thyroid function - Regular monitoring of thyroid function is important during the postpartum period, especially for women with postpartum thyroiditis 4

3. Be aware of risk factors - Women with previous episodes of postpartum thyroiditis, Graves' disease, Hashimoto's thyroiditis, thyroid peroxidase antibody positivity, type 1 diabetes, or other autoimmune diseases are at higher risk for postpartum thyroid dysfunction 4

4. Distinguish between conditions - If thyrotoxicosis occurs postpartum, it's important to differentiate between new-onset/recurrent Graves' disease and postpartum thyroiditis, as management differs 4

In conclusion, levothyroxine treatment for postpartum thyroiditis is safe during breastfeeding and does not negatively affect the breastfed infant. Proper treatment may actually improve milk production in hypothyroid mothers, benefiting both mother and child.