When to initiate treatment for hypothyroidism (underactive thyroid) in a breastfeeding patient?

From the Guidelines

Breastfeeding patients with hypothyroidism should be treated when they have elevated TSH levels, typically above 10.0 mIU/L, as this threshold is generally considered the point for initiation of treatment, according to expert opinion 1.

Key Considerations

• The decision to start therapy in patients with TSH levels between 4.5 and 10.0 mIU/L is more controversial, and a large magnitude of overdiagnosis and overtreatment is a likely consequence of screening for thyroid dysfunction 1.
• Levothyroxine is considered safe during breastfeeding as minimal amounts pass into breast milk.
• TSH levels should be monitored 4-6 weeks after starting treatment and then every 6-12 months once stable, with dose adjustments as necessary to maintain TSH between 0.5-2.5 mIU/L.

Treatment Approach

• The standard treatment is levothyroxine (Synthroid, Levoxyl), usually starting at 1.6 mcg/kg/day, taken on an empty stomach 30-60 minutes before breakfast or 3-4 hours after the last meal of the day.
• Patients should be advised not to take levothyroxine with calcium supplements, iron, or certain foods that may interfere with absorption.

Rationale

• Untreated hypothyroidism in breastfeeding mothers can lead to decreased milk production and potentially affect infant development, so prompt treatment is important.
• Levothyroxine helps restore normal thyroid hormone levels, which are essential for metabolism, energy production, and milk supply.
• The USPSTF found no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes, but expert opinion suggests treating patients with TSH levels above 10.0 mIU/L 1.

From the FDA Drug Label

The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for levothyroxine sodium and any potential adverse effects on the breastfed infant from levothyroxine sodium or from the underlying maternal condition Adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply

• Treatment of hypothyroidism in breastfeeding mothers should be based on the mother's clinical need for levothyroxine sodium.
• The decision to treat should consider the developmental and health benefits of breastfeeding and potential adverse effects on the breastfed infant.
• Adequate treatment may help normalize milk production in hypothyroid lactating mothers with low milk supply.
• No specific guidelines are provided for when to initiate treatment, but it is implied that treatment should be given when clinically necessary, as the benefits of breastfeeding should be weighed against the mother's need for levothyroxine sodium 2.

From the Research

Treatment of Hypothyroidism in Breastfeeding Women

• The provided studies do not specifically address the treatment of hypothyroidism in breastfeeding women 3, 4, 5, 6, 7.
• However, it can be inferred that the treatment of hypothyroidism in breastfeeding women would follow similar guidelines as for non-breastfeeding women, with the goal of achieving normal thyroid-stimulating hormone (TSH) levels and relieving symptoms.
• According to 3, women with hypothyroidism who become pregnant should increase their weekly dosage of levothyroxine by 30%, but it is not specified if this applies to breastfeeding women as well.
• In general, the treatment of hypothyroidism involves levothyroxine replacement therapy, started at a dosage of 1.5 to 1.8 mcg per kg per day, with adjustments made based on TSH levels and symptoms 3, 4, 5.
• It is essential to note that the decision to treat subclinical hypothyroidism should be made on a case-by-case basis, taking into account the patient's age, risk factors, and comorbid conditions 4, 6.

Subclinical Hypothyroidism

• Subclinical hypothyroidism is defined as elevated TSH levels with normal free triiodothyronine (FT3) and free thyroxine (FT4) levels 4, 6.
• The diagnosis of subclinical hypothyroidism should be confirmed by repeat thyroid function tests, ideally obtained at least 2 months later, as 62% of elevated TSH levels may revert to normal spontaneously 4.
• Treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L, and even then, the decision to treat should be made on a case-by-case basis 4, 6.

Levothyroxine Treatment

• Levothyroxine replacement therapy is the standard treatment for hypothyroidism, with the goal of achieving normal TSH levels and relieving symptoms 3, 4, 5.
• The dosage of levothyroxine should be adjusted based on TSH levels and symptoms, with the goal of achieving a TSH level within the normal range 3, 4, 5.
• Combined treatment with levothyroxine and liothyronine may be preferred in some patients, especially those with a polymorphism in type 2 deiodinase 4, 7.