Yes. Even if mom’s thyroid levels are not controlled by medication (or are in the process of being controlled) it is safe for mom to breastfeed her baby.
Moms who are hypothyroid have low thyroid hormone levels and elevated TSH (thyroid stimulating hormone) levels. Symptoms include cold intolerance, weight gain, dry skin, thinning hair, poor appetite, fatigue, depression and reduced milk supply.
Per Medications and Mothers’ Milk (Hale 2002, p. 690-691), “Thyroid stimulating hormone (Thyrotriopin, TSH) is known to be secreted into breastmilk. TSH is extremely elevated in hypothyroid mothers and could presumably cause a hyperthyroid condition in the breastfeeding infant.” However, Hale goes on to cite a study which found only low levels of TSH in the breastmilk of a mom with high TSH levels, “suggesting that human breastmilk does not contain excessive amounts of TSH in the presence of severe maternal hypothyroidism, and that breastfeeding is permissible in hypothyroid mothers.”
Untreated low thyroid levels in mom may result in a decrease in milk supply and sometimes poor weight gain in baby (due to low milk supply). Per Breastfeeding and Human Lactation (Riordan & Auerbach 1999, p. 543-544), “If replacement therapy of thyroid extract… is adequate, the relief of the symptoms and an increase in the milk supply can be quite dramatic.”
Moms who are hyperthyroid have elevated thyroid hormone (usually T4) levels. Symptoms include weight loss (despite an increased appetite), nervousness, heart palpitations, insomnia, and a rapid pulse at rest.
Hyperthyroidism is not a contraindication for breastfeeding. Per Medications and Mothers’ Milk (Hale 2002, p. 417-418, 423-424), only exceedingly low levels of thyroid hormones (both T4 and T3) transfer into breastmilk.
In animal studies, high thyroid levels interfered with milk let-down (Lawrence & Lawrence 1999, p. 522).
Mothers who have the autoimmune forms of thyroid disease will usually have thyroid autoantibodies present in their blood. Hypothyroidism is most commonly caused by Hashimoto’s Thyroiditis, an autoimmune thyroid disease in which the immune system attacks and destroys the thyroid gland, resulting in underproduction of thyroid hormone. Another common autoimmune thyroid disease is Grave’s Disease, which is a leading cause of hyperthyroidism; in this disease the antibodies attacking the thyroid gland cause growth of the gland and overproduction of thyroid hormone. Some mothers may be worried that these antibodies may pass into breastmilk and harm baby, however this is not a concern. The thyroid autoantibodies are IgG immunoglobulins, which are too large to pass into breastmilk. Continuing to breastfeed will only benefit your baby, as babies who are artificially fed are at increased risk of developing autoimmune thyroid disease themselves.
There is evidence that breastfeeding can help to prevent thyroid problems in both mom and baby.
- Breastfeeding helps to prevent autoimmune thyroid disease (Fort 1990).
- Breastfeeding may help to prevent thyroid cancer in mom (Mack 1999).