The importance of iodine and thyroid health in pregnancy


Iodine deficiency is rampant in the Western world. Mostly due to the fact that our diets are so deficient in this crucial nutrient. The main sources of dietary iodine are found in seafood and seaweed, and these foods are very low in a standard Australian diet.  Other causes for iodine deficiency are the fact our soil's content is low, and we are exposed to halogens such as fluoride, bromine and chloride. These compounds look similar in structure to iodine when in the body, and these minerals take all the seats up where iodine would normally be in the body's cells, so there is no room for iodine to be absorbed.  The government tried to overcome this, by making it compulsory for bread to be fortified with iodine, however, studies have shown this has not significantly improved iodine levels in our most at-risk population- pregnant women.

Iodine is crucial for a woman’s thyroid when pregnant and also when not. It is also extremely important for the healthy growth of the baby, in particular, brain health.

In pregnancy, our output of thyroid hormone increases to help with the growth of the baby. Our thyroid hormones are made up of iodine, and hence no iodine, no thyroid hormone. When the body is even slightly deficient in thyroid hormones (TSH > 2.5mIU/L) in the first trimester, the risk of miscarriage doubles.

Iodine adequacy is also crucial for the development of the baby, in particular, their brain development in learning. Mild cognitive impairments have been found in offspring born to mildly iodine-deficient mothers.  In an Australian study, the children whose mothers had a urinary iodine of less than 150mcg/ L compared to those born with iodine adequacy had reductions of:

-       10% in spelling

-       7.6 % in grammar

-       5.7% in English-literacy.

An iodine deficiency midway through the pregnancy can produce irreversible brain damage.


This is not to say we all need to go out and take copious amounts of iodine. The range for an ideal iodine level is extremely small, and iodine excess can be just as damaging to the mother and growing baby. These include:

-       Higher rates of autoimmune thyroid disease and subclinical hypothyroidism in the mother

-       Three times the risk of developing post-partum thyroiditis.

-       Increased risk of subclinical hypothyroidism in the baby once born.


So how do you find out if you're in the risk zone?

I recommend every woman follow a preconception plan prior to falling pregnant. Your GP should be happy to assess your thyroid hormones and thyroid autoantibodies. A random urinary spot iodine is also important to be assessed. Medicare will not generally run these, and will usually need to be arranged through your naturopath, with an out-of-pocket expense.  It is important to remember that the thyroid requires other minerals such as iron, zinc and selenium to function properly, and these can also be assessed by a blood test.


So what do an adequate thyroid hormone and iodine level look like in pregnancy?

Before preconception-  You should be aiming for a TSH between 1-2mIU/L., and no elevated thyroid autoantibodies. A TSH at > 2.5mIU/L in the 1st trimester of pregnancy doubles the risk of miscarriage. Your T4 should be sitting above 12, less than this suggests iodine deficiency.

Urinary iodine (corrected for creatinine) should be between 150- 249mcg/L. Remember excess iodine carries just as many risks as too little, so never supplement iodine without doing the testing first!

We all want the best for our children, and preconception is a powerful time in which we can set up our baby's health to be it's absolute best. 


If you are thinking of planning for a baby, Tess is highly skilled in preconception care. Please feel free to contact her at, to get your baby planning underway.