Radioactive Iodine Treatment and Breastfeeding
Lactating women who require radioactive iodine treatment must permanently discontinue breastfeeding immediately and should not resume nursing for the current infant, though breastfeeding in future pregnancies is not contraindicated.
Immediate Management
- Breastfeeding must be stopped permanently for the current infant once therapeutic radioactive iodine (¹³¹I) is administered 1, 2
- Radioactive iodine concentrates significantly in breast milk, creating a direct radiation hazard to the nursing infant's thyroid gland 2
- Even after therapeutic doses, breast milk remains radioactive for extended periods—calculations show that to achieve safe infant doses (<1 mSv effective dose and <10 mSv thyroid dose), breastfeeding would need to cease for at least 52 days 2
Critical Timing Considerations
- Ideally, breastfeeding should be discontinued several days BEFORE radioiodine administration to allow breast tissue involution and reduce radiation dose to the breasts themselves 2
- The estimated equivalent radiation dose to maternal breast tissue after therapeutic ¹³¹I administration during lactation is approximately 1.6 Gy, which represents significant tissue exposure 2
- If emergency treatment is required, immediate cessation is mandatory at the time of administration 1
Absolute Contraindications
- Pregnancy and lactation are absolute contraindications to radioiodine therapy 3
- Treatment should be deferred until after lactation is complete, or breastfeeding must be permanently stopped before proceeding 3
Future Pregnancy and Lactation
- Breastfeeding in subsequent pregnancies after radioiodine treatment is NOT contraindicated—women can safely nurse future children 1
- This applies only to future pregnancies; the current nursing relationship must end permanently 1
Diagnostic vs. Therapeutic Doses
- Even standard diagnostic doses of ¹³¹I require permanent cessation of breastfeeding for that infant 1
- For diagnostic studies in lactating women, ¹²³I-labeled radiopharmaceuticals are preferable to ¹³¹I agents when studying the thyroid, though breastfeeding interruption is still required 4
- Shorter-lived technetium-labeled agents may only require 24-hour cessation of nursing, making them preferable for non-thyroid diagnostic studies in lactating women 4
Common Pitfalls to Avoid
- Do not allow resumption of breastfeeding after therapeutic ¹³¹I even if milk radioactivity appears to decline—the prolonged excretion period and infant thyroid sensitivity make this unsafe 2
- Do not proceed with radioiodine therapy without confirming lactation status—this is a critical pre-treatment screening question 3
- Pregnant women and young children in the household also require stringent protection measures due to higher radiation sensitivity, so standard post-treatment isolation guidelines must be followed 5, 1