Breastfeeding and Thyroid Disease: What Should You Know?

Mary Shomon | July 25, 2017

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Breastfeeding is a healthy choice for both mother and baby. Babies find nutrient- and antibody-rich breast milk easiest to digest; plus breast milk enhances babies’ immunity against many illnesses and is linked to reduced risks of allergies, asthma, obesity, diabetes, and sudden infant death syndrome. For nursing mothers, breastfeeding may reduce the risk of ovarian and breast cancer. If you have difficulty breastfeeding, be aware, however, that there is an often-overlooked link to thyroid disease.

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Track your milk production

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Thyroid problems, especially hypothyroidism, increase your risk of low milk supply. When you are unable to produce enough milk, there are several key signs:

  • Your baby is losing weight.
  • Your baby is gaining weight slowly or not at all.
  • Your baby is not having a typical number of daily bowel movements and wet diapers.
  • When pumping breast milk, you regularly get less than three ounces per session.
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Make sure you get enough iodine

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Successful milk production requires healthy thyroid function. And healthy thyroid function relies on adequate iodine levels. If you are breastfeeding, whether or not you have a thyroid condition, experts recommend you get at least 290 mcg of iodine daily. Discuss with your doctor whether you should supplement with iodine while nursing to ensure you have adequate levels.

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Get a thyroid evaluation if you’re having breastfeeding issues

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Childbirth raises your risk of developing a new thyroid problem. If you are having milk supply complications, immediately request a complete thyroid evaluation to rule out hypothyroidism. This should include a thyroid stimulating hormone (TSH) test, as well as tests for free thyroxine (free T4) and free triiodothyronine (free T3). This evaluation is even more crucial if you have other symptoms such as fatigue, hair loss, difficulty losing weight, rapid weight loss, or depression.

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Get your thyroid checked a few weeks after childbirth

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After childbirth, it is common for thyroid levels to change as a result of postpartum shifts in estrogen and progesterone. If you are having difficulty breastfeeding, schedule an evaluation of your thyroid as soon as possible. Your doctor should check your TSH, free T4, and free T3 levels, and adjust your treatment as necessary.

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Don't stop taking your thyroid hormone replacement medication

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You’ve heard the warnings about taking medications while breastfeeding. It’s important, however, to continue taking your thyroid hormone replacement medication, like levothyroxine (Synthroid, Levoxyl, Tirosint) or natural desiccated thyroid (Nature-Throid, Armour). Not only is it safe to continue taking these drugs, it’s necessary for healthy breastfeeding. If you’re on the correct dose, very little medication passes to the baby via breast milk.

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Talk to your doctor about which antithyroid drugs are safest

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If you are hyperthyroid, experts consider it safe for you to take the antithyroid drugs methimazole and carbimazole (Tapazole, Neo-Mercazole) while breastfeeding, but they do not recommend propylthiouracil (PTU). When you are on the correct dose, the amount of antithyroid drugs that pass into your breast milk is considered insignificant. You should, however, have your thyroid evaluated frequently, including TSH and free T4 tests.

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Avoid overmedication

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When breastfeeding, be careful not to take too much thyroid medication, whether thyroid hormone replacement medication or antithyroid drugs. If you are significantly overmedicated, the excess may pass through breast milk to your baby, negatively affecting his or her thyroid. Frequent thyroid testing is the best way to ensure that you are on the right dosage.

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Discontinue breastfeeding if you need radioactive iodine treatment

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Radioactive iodine, known as RAI, is a treatment option for Graves’ disease, hyperthyroidism, and goiter, and in some cases it is administered after surgery for thyroid cancer. According to the American Thyroid Association, RAI is never performed on a woman who is pregnant or breastfeeding. The radioactivity can damage your baby’s thyroid, and make him or her hypothyroid. If you need RAI treatment, you will need to discontinue breastfeeding.

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Consider alternatives to a radioiodine uptake (RAI-U) test

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If you may have Graves’ disease, hyperthyroidism, or thyroid cancer, your doctor may order a radioiodine uptake (RAI-U) test. The regular RAI-U test is never done on a breastfeeding woman. Your doctor can, however, use radioactive technetium instead of radioactive iodine to perform an uptake scan. You should refrain from breastfeeding after the test. Ask your doctor how long you need to “pump and dump” (discard pumped breast milk) before it’s safe to resume breastfeeding.