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T3 and Breastfeeding

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  • T3 and Breastfeeding

    I am breastfeeding and take Synthroid. My doctor and I have discussed adding Armour or Cytomel because my Free T3 is a bit low. Are these medications safe for my baby, and is one preferred over the other? Would my baby need any testing due to my use of thyroid medication? Thank you!

  • #2
    Dr. Hale and I have discussed this question. Most studies indicate that minimal levels of maternal thyroid, synthetic or otherwise, are transferred into human milk. Since a hypothyroid mother takes Synthroid to correct a hormonal deficiency, the amount of hormone that gets out into the milk is very similar to what the mother would secrete if she had a normally functioning thyroid to begin with. Therefore, the risk of breast feeding on Synthroid is no greater than that of a mother with normal thyroid function and not on Synthroid. We give Synthroid (levothyroxine) an "L1" - the safest category of lactation risk.

    Cytomel (synthetic liothyronine, T3) enters the breast milk more readily than levothyroxine but still at very low levels. The argument about hormone deficiency applies here as well. We give Cytomel an "L2" (out of 5) ("Probably safe"), mainly due to the scarcity of data in the literature.

    Armour thyroid is an extract from pig thyroid that contains all thyroid hormones in roughly the same proportion as they are secreted by a human's. There is some debate among endocrinologists regarding Armour vs Cytomel. Cytomel is a powerful, purified product and is therefore easier to dose and control. Armour is a gentler product but is sometimes variable in its contents, can be difficult to obtain due to manufacturing shortages, and has been associated with allergic reactions to the thyroid tissue remnants left in the pill. We are not qualified to make a definitive recommendation in your case. It will depend on what your physician is comfortable prescribing - what he or she has the most experience using and managing.

    Thyroid supplements, taken as prescribed, are not likely to cause problems for a nursing baby. No further testing should be necessary. In most areas, including ours, thyroid testing is a part of routine neonatal screening done by the state health department. Ask your pediatrician if this has been done for your baby already.

    Please call us at the InfantRisk Center if this has not completely answered your question. (806)352-2519

    -James Abbey, MD

    The following references may be useful to your physician if he or she needs more information:
    1. Varma SK, Collins M, Row A, Haller WS, Varma K. Thyroxine, tri-iodothyronine, and reverse tri-iodothyronine concentrations in human milk. J Pediatr 1978; 93(5):803-806.
    2. Hahn HB, Jr., Spiekerman AM, Otto WR, Hossalla DE. Thyroid function tests in neonates fed human milk. Am J Dis Child 1983; 137(3):220-222.
    3. Sack J, Amado O, Lunenfeld B. Thyroxine concentration in human milk. J Clin Endocrinol Metab 1977; 45(1):171-173.