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PubMed This is a summary of 13 peer-reviewed journal articles Updated
Pediatrics · Iodine-Induced Infant Hypothyroidism

Protecting Your Baby: Iodine Risks in Pregnancy and Infancy

At a Glance

Excessive iodine from maternal diets, supplements, or medical contrast dye can temporarily shut down a newborn's thyroid gland. Preterm infants are at highest risk. Doctors monitor thyroid levels after exposure and may prescribe temporary levothyroxine to protect the baby's developing brain.

For parents and guardians, iodine can be a confusing topic. You may have heard that iodine is essential for your baby’s brain development, yet your doctor is now concerned that your baby has “too much” of it. This is because the thyroid gland in newborns—and especially in preterm infants—is incredibly sensitive to the amount of iodine it receives.

The “Goldilocks” Mineral

Your baby’s thyroid needs a “just right” amount of iodine. While chronic deficiency is dangerous for fetal development, a sudden flood of iodine can cause the baby’s thyroid to shut down entirely (the Wolff-Chaikoff effect) [1][2].

Why Preterm Babies Are at Higher Risk

Full-term babies have a “safety switch” that allows their thyroid to restart after a brief shutdown. However, preterm infants often have immature thyroid glands that lack this ability to “escape” the shutdown [3]. When they are exposed to high doses of iodine—such as from contrast dye used in medical scans or heart procedures—their thyroid may stay “off” for several weeks [3][4].

The Role of Maternal Diet (Seaweed Soup)

Iodine is highly concentrated in breast milk. If a nursing mother consumes very high amounts of iodine, her baby will receive an even larger dose [1].

  • Traditional Foods: In some cultures, high-iodine foods like seaweed soup are traditionally eaten after birth. While nutritious, extreme amounts (exceeding 500 mcg/day) can inadvertently trigger hypothyroidism in the newborn [5][6].
  • Safe Supplementation: The latest 2026 ATA guidelines continue to recommend that pregnant and breastfeeding women take a daily multivitamin containing 150 mcg of iodine to ensure adequate—but not excessive—levels [7][8].

Monitoring Your Baby After Iodine Exposure

If your baby has been exposed to a large amount of iodine (for example, through a CT scan or a heart catheterization), guidelines recommend a specific monitoring schedule to ensure their thyroid restarts:

  1. Baseline Testing: Checking TSH and free T4 (fT4) levels shortly after the exposure [3].
  2. Follow-up: Repeat testing at 2 weeks and 6 weeks after exposure [9][10].
  3. Treatment: If the baby’s TSH is significantly high (≥10 mU/L), doctors may start a temporary course of levothyroxine to protect the baby’s developing brain while the iodine clears their system [11].

Stabilizing Facts for Parents

  1. Detection is half the battle: Because of newborn screening and specialized monitoring after medical tests, these shifts are usually caught early [1][12].
  2. It is often temporary: Most babies’ thyroids will “restart” on their own once the excess iodine is gone [5][13].
  3. Thyroid hormone is safe: If your baby needs temporary hormone replacement, it is the same hormone their body would naturally produce, and it is vital for their brain growth [11].

Common questions in this guide

Why is excess iodine dangerous for my premature baby?
Preterm infants have immature thyroid glands that cannot easily restart after being shut down by a sudden flood of iodine. This temporary shutdown can last for several weeks and may impact early brain development if not properly monitored and treated.
Can the iodine in my breast milk affect my baby's thyroid?
Yes, iodine is highly concentrated in breast milk. If a nursing mother consumes very high amounts of iodine, such as eating large daily portions of seaweed soup, it can pass to the baby and temporarily suppress their thyroid function.
How much iodine should I take while pregnant or breastfeeding?
Current guidelines recommend that pregnant and breastfeeding women take a daily multivitamin containing exactly 150 micrograms of iodine. This provides the right amount for your baby's development without causing an overload.
What happens if my baby is exposed to iodine from medical contrast dye?
If your baby receives iodine contrast dye for a medical scan or heart procedure, their thyroid levels will be closely monitored. Doctors will typically check their TSH and free T4 levels shortly after the exposure, and again at two weeks and six weeks.
Will my baby need treatment for iodine-induced hypothyroidism?
If your baby's thyroid levels drop, doctors may prescribe a temporary course of levothyroxine. This is the exact same hormone their body naturally produces, and it is a safe, vital treatment to protect your baby's brain while the excess iodine clears.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Given that my baby was born prematurely, how does that affect their ability to handle the iodine from the recent contrast dye?
  2. 2.How many follow-up thyroid tests will my baby need, and what specific numbers are you looking for?
  3. 3.Is the iodine level in my breast milk potentially contributing to my baby’s low thyroid levels?
  4. 4.Should I temporarily stop my prenatal vitamins or avoid specific foods like seaweed while we monitor my baby's thyroid?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (13)
  1. 1

    Maternal iodine excess: an uncommon cause of acquired neonatal hypothyroidism.

    Hamby T, Kunnel N, Dallas JS, Wilson DP

    Journal of pediatric endocrinology & metabolism : JPEM 2018; (31(9)):1061-1064 doi:10.1515/jpem-2018-0138.

    PMID: 30052521
  2. 2

    Elemental analysis of the thyroid by laser induced breakdown spectroscopy.

    Ahmed I, Ahmed R, Yang J, et al.

    Biomedical optics express 2017; (8(11)):4865-4871 doi:10.1364/BOE.8.004865.

    PMID: 29188087
  3. 3

    The effect of iodinated contrast media on thyroid (dys)function in children.

    Vancauwenbergh F, Decallonne B, Rochtus AM

    European thyroid journal 2026; (15(4)) doi:10.1530/ETJ-26-0036.

    PMID: 42340805
  4. 4

    The effect of cardiac catheterization on thyroid functions in infants with congenital heart diseases: a prospective observational study.

    Elbaz BA, Elmarsafawy HM, Laimon WN

    European journal of pediatrics 2025; (184(2)):137 doi:10.1007/s00431-024-05934-4.

    PMID: 39812893
  5. 5

    Effect of Maternal Iodine Excess during Pregnancy on Neonatal Thyroid Function and Neurodevelopmental Status at 12 Weeks.

    Rao DK, Jindal A, Dabas A, et al.

    Journal of the ASEAN Federation of Endocrine Societies 2024; (39(2)):27-32 doi:10.15605/jafes.039.02.12.

    PMID: 39620182
  6. 6

    Adverse Effects on the Thyroid of Chinese Pregnant Women Exposed to Long-Term Iodine Excess: Optimal and Safe Tolerable Upper Intake Levels of Iodine.

    Wu W, Guo W, Zhang N, et al.

    Nutrients 2023; (15(7)) doi:10.3390/nu15071635.

    PMID: 37049475
  7. 7

    American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum.

    Korevaar TIM, Leung AM, Alexander EK, et al.

    Thyroid : official journal of the American Thyroid Association 2026; (36(5)):481-544 doi:10.1177/10507256261445624.

    PMID: 42219800
  8. 8

    Iodine supplementation for pregnant women: a cross-sectional national interventional study.

    Delshad H, Raeisi A, Abdollahi Z, et al.

    Journal of endocrinological investigation 2021; (44(10)):2307-2314 doi:10.1007/s40618-021-01538-z.

    PMID: 33704696
  9. 9

    Screening of congenital hypothyroidism in preterm, low birth weight and very low birth weight neonates: A systematic review.

    Hashemipour M, Hovsepian S, Ansari A, et al.

    Pediatrics and neonatology 2018; (59(1)):3-14 doi:10.1016/j.pedneo.2017.04.006.

    PMID: 28811156
  10. 10

    Thyroid dysfunction associated with iodine-contrast media: A real-world pharmacovigilance study based on the FDA adverse event reporting system.

    Huang L, Luo Y, Chen ZL, et al.

    Heliyon 2023; (9(11)):e21694 doi:10.1016/j.heliyon.2023.e21694.

    PMID: 37954365
  11. 11

    How can the occurrence of delayed elevation of thyroid stimulating hormone in preterm infants born between 35 and 36 weeks gestation be predicted?

    Heo YJ, Lee YA, Lee B, et al.

    PloS one 2019; (14(8)):e0220240 doi:10.1371/journal.pone.0220240.

    PMID: 31442229
  12. 12

    One children's hospital planning and development process to adhere to the FDA recommendation that babies and young children undergo thyroid function testing after receiving an injection of iodine-containing contrast media for medical imaging.

    Bardo DME, Samis JH, Josefson JL, et al.

    Pediatric radiology 2024; (54(1)):27-33 doi:10.1007/s00247-023-05806-3.

    PMID: 38030850
  13. 13

    Effects of iodine contrast media on thyroid function - a prospective study.

    Carlqvist J, Nyman U, Brandberg J, et al.

    European thyroid journal 2024; (13(6)).

    PMID: 39400593

This page provides educational information about iodine's effect on infant thyroid function. Always consult your pediatrician or pediatric endocrinologist for specific medical advice, testing schedules, and treatment plans for your baby.

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