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Iodine in the third trimester | Pregnancy Power Hour
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Nutrition · trimester 3 · Mineral

Iodine in the third trimester

RDI: Pregnancy RDA: 220 mcg/day (US); 250 mcg/day (WHO); UL: 1100 mcg/day

In the third trimester, consistent iodine intake remains vital for your baby's continued brain development and to support your body's sustained metabolic needs through late pregnancy and into breastfeeding.

2 min read

Quick answer

In the third trimester, consistent iodine intake remains vital for your baby's continued brain development and to support your body's sustained metabolic needs through late pregnancy and into breastfeeding.

As you navigate the final months of pregnancy, the demand for iodine remains significant, playing a critical role in your baby's ongoing neurological development and supporting your own thyroid function. While often discussed in early pregnancy, iodine's importance doesn't diminish in the third trimester; rather, it's about sustaining adequate levels for both you and your baby's maturation. Evidence suggests that mild iodine deficiency is widespread globally, including in pregnant populations in the US and UK. The World Health Organization (WHO) highlights iodine deficiency in pregnancy as the leading preventable cause of intellectual disability worldwide, underscoring why consistent attention to this mineral is so important throughout your entire pregnancy.

Meeting your iodine needs primarily through food is a gentle, effective approach. Key sources include iodized salt, dairy products, various types of seafood, and seaweed. It's worth noting that many common salts, like sea salt and kosher salt, are typically not iodized, so checking labels can be helpful if you rely on salt for iodine intake. While we often focus on minerals like Calcium in the third trimester for bone development, or Iron in the third trimester for blood volume, iodine's contribution to cognitive development is equally foundational, ensuring a broad spectrum of support for your growing baby.

For many, a prenatal vitamin can help bridge any dietary gaps. Many prenatal vitamins contain around 150 mcg of iodine, which can be a helpful contribution. The goal is for your total daily intake, combining both food and supplements, to reach approximately 220-250 mcg. This collaborative approach ensures you're thoughtfully supporting your body's needs. However, it's also important to be mindful of excessive intake; research indicates that consuming more than 1100 mcg per day can lead to thyroid issues. Kelp supplements, in particular, can have highly variable iodine content and should be approached with caution, as they can sometimes lead to excessive levels.

Considering the long-term impact on cognitive function, ensuring clear and confident iodine intake is a practical step you can take for your baby's development. The WHO's universal salt iodization program stands as one of the most successful public health interventions, demonstrating the profound positive effects of widespread iodine availability. This historical context reinforces the value of being informed about your personal intake. As with any aspect of your prenatal nutrition, discussing your dietary choices and supplement plan with your care provider is always your best resource for your specific situation. They can offer personalized guidance to help you make informed decisions.

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Common questions

Why is iodine still important in the third trimester?+

Iodine is crucial for your baby's continued brain development and to support your own thyroid function, which remains elevated through late pregnancy and into breastfeeding.

Can I get enough iodine from food alone?+

While food sources like iodized salt, dairy, and seafood are excellent, mild iodine deficiency is widespread, so many find a prenatal supplement helpful to reach the recommended intake.

Is it possible to have too much iodine?+

Yes, excessive iodine intake, particularly above 1100 mcg/day, can lead to thyroid problems. This is especially a concern with certain high-dose supplements like kelp.

Brittany Nance

“Pregnancy is under-supported at every week. This is the kind of clear, calm guidance I give my one-on-one clients — and the questions worth taking back to your provider.”

Brittany Nance · Pregnancy Wellness Consultant · full-spectrum doula

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Written by Brittany Nance, Pregnancy Wellness Consultant· BADT Full Spectrum Doula · Founder, Pregnancy Power Hour
Last reviewed July 1, 2026

This is evidence-informed education from a birth-doula perspective, not medical advice. Always discuss your individual situation with your prenatal care provider.

Keep reading

  • RelatedIodine in the second trimesterIn the second trimester, adequate iodine intake remains crucial for your baby's ongoing brain development and thyroid function, building on the foundation laid in early pregnancy.
  • RelatedIodine in the first trimesterIn the first trimester, your baby's developing brain and nervous system rely entirely on your thyroid hormone, making adequate maternal iodine intake particularly crucial.
  • RelatedSelenium in the third trimesterIn the third trimester, selenium continues its vital role as an antioxidant and supports thyroid function, both essential for your well-being and your baby's final development.
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  • RelatedSeaweed and Nori in the third trimesterEnjoying seaweed and nori in your third trimester is generally fine, but understanding iodine levels and sourcing helps you make informed choices.
  • RelatedDHA — Omega-3 in the third trimesterThe third trimester is a pivotal time for DHA accumulation in your baby's developing brain and retina, making informed intake especially supportive.