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| Eyla Boies MD, FAAP
Hyper and hypothyroid conditions are common in women of child-bearing age especially in the postpartum period. As a result, questions regarding breastfeeding and maternal thyroid disease, including safety of thyroid medication while breastfeeding are frequently encountered. Hypothyroidism: It is important for the woman who is hypothyroid to receive adequate thyroid replacement during pregnancy to assure she carries a healthy fetus to term. When thyroid hormone is given to the lactating mother, it is given in amounts to attain a euthyroid state, i.e., normal levels of thyroid hormone. Thus the amount of thyroid hormone an infant is exposed to in breastmilk of a mother on thyroid replacement is the same as that in the mother who is not hypothyroid and is producing adequate amounts of her own thyroid hormone. As Dr. Ruth Lawrence states, " the mother should be permitted to breastfed without question." In rare cases undiagnosed hypothyroidism may be the cause of insufficient milk production. When clinically indicated it may be prudent to check her thyroid stimulating hormone (TSH). Hyperthyroidism: Clinical hyperthyroidism is rare during pregnancy (0.2% of all pregnancies). However, postpartum thyroiditis may occur in up to 5% of mothers. Postpartum thyroiditis (PPT) initially presents with an over production then after about six weeks an insufficient production of thyroid hormone. The initial hyperthyroid symptoms of PPT are generally mild and can be controlled with propranolol, a medication that is compatible with breastfeeding. Symptoms may be more severe in mothers who have Graves disease. In this case Propylthiouracil (PTU), methimazole (Tapazole), or carbmazole (derivative of methimazole) all medications that block the iodination of the tyrosine molecule thus inhibiting synthesis of thyroid hormone are indicated. An infant may develop a goiter and symptoms of hypothyroidism if exposed to these medications in sufficient doses. Methimazole is secreted into breastmilk (Milk/Plasma ratio =1). Studies by Lamberg et al and Azizi found no adverse effect on thyroid function of infants whose mothers were taking modest doses of carbimazole and methimazole respectively. Very little PTU is secreted into breastmilk since it is highly protein bound. Kampmann, et al found no evidence of adverse effect on infant thyroid function in nine mothers taking PTU. PTU is the preferred medication in the lactating mother since very little gets into breast milk, however, when given in modest doses methimazole (up to 20 mg/day) is compatible with breastfeeding. All breastfeeding infants whose mothers are taking any of these medications should have thyroid functions closely monitored as well as careful clinical follow-up of the infant checking for signs and symptoms of hypothyroidism in the first few weeks and months of life. The older infant (> 6 months of age) who is receiving solid foods is unlikely to experience problems.Some women who had Graves disease may have undergone thyroid ablation and be clinically hypothyroid requiring thyroid hormone replacement. It is important to know and understand that her primary diagnosis was an autoimmune process and she may still have antibodies against the thyroid that can pass across the placenta and cause transient |
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hyperthyroidism in the neonate. We recently had such a case where a breastfeeding infant was failing to gain weight. Some providers might have first "blamed" breastfeeding as the problem. The provider in this case obtained a careful maternal and breastfeeding history, test weight after breastfeeding in the office, and thyroid function tests on the infant and made the diagnosis of transient neonatal hyperthyroidism.
The diagnostic evaluation of a lactating hyperthyroid mother can be problematic. Thyroid imaging scans using 131 I are frequently used in sorting out the diagnosis of hyperthyroidism. Radioactive 131 I has a long half-life and is sequestered in high concentrations in breastmilk. Based on the rate of radioactive decay breastmilk might be safe to consume 40 days after 131I administration, however, this is not known with certainty. Breastmilk would need to be counted by a gamma counter prior to resumption of breastfeeding. In essence, the administration of 131 I is not compatible with breastfeeding. Every attempt should be made to make the diagnosis without the use of a 131 I thyroid scan.In summary, most lactating mothers on medications for hyperthyroidism can continue to breastfeed with careful clinical and biochemical monitoring of the infant. Thyroid hormone therapy when given to the lactating mother in appropriate doses poses no risk to the infant. Radioactive 131 I use in the diagnostic imaging of the thyroid is not compatible with breastfeeding. It is important to know the underlying diagnosis of a mother on thyroid hormone replacement because 5% of babies born to mothers with Graves disease will have transient neonatal hyperthyroidism. Lastly, insufficient breastmilk production may be the result of hypothyroidism. References |
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