Thyroid hormone problems

How will my thyroid problem affect my milk supply?

The thyroid is a gland in the front of the neck that produces important hormones. Diseases of the thyroid, such as postpartum thyroiditis, which develops after delivering a baby, can cause abnormal hormone levels. Low thyroid levels have been shown to decrease milk supply, but once a mother receives treatment, the milk supply may increase. A breastfeeding mother who is newly diagnosed with postpartum thyroiditis or other thyroid diseases and has a baby who is growing normally should not see any decrease in milk supply if treatment is started with ongoing monitoring. Mothers with stable, long-standing thyroid problems that are monitored should not expect their condition to impact breastfeeding. While rare, it is possible for high levels of thyroid hormones to cause a large milk supply. While medication used to treat thyroid problems can be safely used by breastfeeding mothers, mothers should not breastfeed if receiving treatment with certain radioactive agents.

A) Describing thyroid hormone problems

The thyroid is a gland in the neck just below the Adam’s apple. It makes important hormones (T3 and T4) that contain iodine. Both hormones act in the same manner. 

Problems with the thyroid gland can result in hormone levels that are too low or too high. Both problems can be missed by health-care providers since the symptoms are often attributed to the stress of having a new baby. Hormone levels are measured with a blood test.

1) Low thyroid hormone levels

Low thyroid hormones in adults can cause the following:

  • Mental slowing and feeling sluggish
  • Weight gain
  • A low body temperature and feeling cold most of the time
  • A lack of energy

2) High levels of thyroid hormones:

High levels of thyroid hormones in adults can cause the following:

  • Feelings of irritability, anxiousness, and restlessness
  • A rapid heart rate
  • Weight loss
  • Individuals to feel hot most of the time

B) Effect of thyroid hormone problems on breastfeeding

1) Effect on milk supply

Low thyroid levels in the mother have been shown to result in a decrease in milk supply (Alexander 2017; Hapon 2003; Joshi 1993). High levels of thyroid hormone have been reported to cause mothers to make too much milk

a) Newly diagnosed thyroid problems

If a mother’s milk supply is reduced because of low thyroid hormone levels, it may increase once she receives treatment. Her baby should be supplemented with milk until the milk supply has recovered.

A breastfeeding mother who is newly diagnosed with thyroid problems and has a baby who is growing well should not see any decrease in supply if treatment is started with ongoing monitoring.

b) Long-standing thyroid problems

Mothers with long-standing thyroid problems that are monitored and treated during and after pregnancy are unlikely to have any breastfeeding difficulties related to their thyroid problems.

2) Effect of treatment

Low levels of thyroid hormones are usually treated by giving synthetic thyroid hormone. This is safe to use while breastfeeding.

Mothers who have high levels of thyroid hormones may need medication to control their symptoms; propothiuacil is commonly used in this situation. It is compatible with breastfeeding. Other treatment can include surgery and radioactive iodine. Mothers who are treated with the latter should not breastfeed and need to wean.

C) Causes of thyroid problems

1) Postpartum thyroiditis

Delivery can affect the thyroid. About 5-10% of new mothers develop postpartum thyroiditis, a general term for inflammation of the thyroid. It may start within one month of delivery and usually ends within the first year. Some mothers with the condition develop abnormally high levels of thyroid hormone and then may have abnormally low levels after several months. Others have consistently low levels. Occasionally, mothers may have permanently low levels.

Postpartum thyroiditis is more common in mothers who also have (Alexander 2017):

  • Diseases in which the body attacks itself (autoimmune) including type 1 diabetes
  • A history of postpartum thyroiditis with a previous baby
  • Other family members with thyroid disease

2) Other thyroid diseases

a) Diseases that cause low levels of thyroid hormone

Low levels of thyroid hormone can be caused by Hashimoto’s thyroiditis or after receiving iodine-based materials for an X-ray or CT scan.

Lack of iodine in the mother’s diet can cause low thyroid hormone levels in both mothers and their newborn babies. 

It is recommended that newborns are tested for thyroid problems after birth, since low levels can affect growth and development. This is done by testing the baby’s blood soon after birth and is offered in many countries (Therrell 2018).

b) Diseases that cause high levels of thyroid hormone

High levels of thyroid hormone can be caused by Graves’ disease and by lumps in the thyroid (nodules).


Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017 Mar;27(3):315-389
Hapon MB, Simoncini M, Via G, et al. Effect of hypothyroidism on hormone profiles in virgin, pregnant and lactating rats, and on lactation. Reproduction. 2003 Sep;126(3):371-82
Joshi JV, Bhandarkar SD, Chadha M, et al. Menstrual irregularities and lactation failure may precede thyroid dysfunction or goitre. J Postgrad Med. 1993 Jul-Sep;39(3):137-41
Therrell BL Jr, Padilla CD. Newborn screening in the developing countries. Curr Opin Pediatr. 2018 Dec;30(6):734-739