Quick answer

NIH lists 220 mcg of iodine a day as the pregnancy need, up from 150 mcg, and puts the upper limit at 1,100 mcg from all sources. A Cochrane review of 14 trials found too few data to judge routine iodine supplements. Ask your doctor before taking more iodine than a prenatal vitamin provides.^1,2,3

Key facts

NIH says pregnant women need about 50% more iodine than other women: 220 mcg a day against 150 mcg.^1,2
The upper limit is 1,100 mcg a day for pregnant adults and 900 mcg for pregnant teens, counting food and supplements together.²
A Cochrane review found too few data to reach firm conclusions on the benefits or harms of routine iodine supplements around pregnancy.³
In a Spanish study, pregnant women who took 200 mcg or more a day from supplements were more likely to have raised TSH than those taking under 100 mcg.²
A prescription potassium iodide label warns of fetal harm, abnormal thyroid function and goiter when it is given in pregnancy.⁴

How much iodine does NIH list for pregnancy?

NIH's consumer fact sheet says women who are pregnant need about 50% more iodine than other women to provide enough for the baby. It lists 220 mcg a day for pregnancy, against 150 mcg for other adults.¹

The reason is the baby's thyroid. Early in pregnancy the baby's own thyroid gland is still forming, so the baby depends entirely on thyroid hormone made by the mother, and her hormone production rises by about 50%. Iodine is the raw material for that hormone.²

Surveys suggest many pregnant women in the United States may not get quite enough iodine. NIH adds that experts do not know whether this affects their babies.¹

What is the upper limit during pregnancy?

The upper limit is the highest daily intake that NIH lists as unlikely to cause harm in most people. It is 900 mcg for pregnant teens aged 14 to 18 and 1,100 mcg for pregnant adults, counting iodine from food, drinks and supplements together. NIH notes that it does not apply to iodine given as medical treatment under a doctor's care.²

In a Spanish study, pregnant women who took 200 mcg or more of iodine a day from supplements were more likely to have raised TSH than those taking less than 100 mcg, a sign that high doses may disturb thyroid function in some women.²

NIH calls this a reason for more research, not a settled finding. It also reports that the American Thyroid Association advises a daily supplement with 150 mcg of iodine for women who are planning a pregnancy, pregnant or nursing, and that the American Academy of Pediatrics advises at least 150 mcg.²

What do trials of iodine in pregnancy show?

A Cochrane review pooled 14 trials of iodine taken before, during or after pregnancy. Its authors found too few data to reach meaningful conclusions on benefits or harms, and rated the evidence behind each finding as low or very low in quality.³

Two results stood out, both low quality. Iodine went with a lower chance of an overactive thyroid after the birth, and one small trial of 76 women found more digestive intolerance during pregnancy with iodine.³

NIH also describes two randomized trials that gave 150 or 200 mcg of iodine a day from early pregnancy. They found no effect on children's thinking, language or movement scores at about 2 years of age.²

Does a prenatal vitamin contain iodine?

Of 89 best-selling US adult multivitamins, 74% contained iodine, with a median of 150 mcg per daily serving, all as potassium iodide. Of 59 prenatal vitamins, 34 contained iodine, from 25 to 290 mcg, and about a quarter of those used kelp.⁵

Kelp and seaweed are the least predictable source. In one analysis of 96 seaweed and kelp products, labels were often inaccurate. Check the Supplement Facts panel for iodine in micrograms, and ask your doctor or pharmacist how it adds to your prenatal vitamin.⁶

What about povidone iodine, nasal iodine and Lugol's solution?

These are different products from the iodine in a vitamin. The label of an over-the-counter povidone iodine antiseptic tells users to stop and ask a doctor if the condition persists or gets worse. It says nothing about pregnancy.⁷

NIH's LactMed database covers breastfeeding rather than pregnancy, but it describes how iodine behaves in the body. Iodine from povidone-iodine is minimally absorbed through intact adult skin, while absorption can be extensive with vaginal use and can be marked on open wounds or mucous membranes.^8,9

Prescription potassium iodide solution is a drug, not a vitamin. Its label warns that potassium iodide can cause fetal harm, abnormal thyroid function and goiter when given to a pregnant woman. For radiation emergencies, FDA says pregnant women and newborns should get priority for evacuation and sheltering, because the drug can suppress thyroid function in the fetus and newborn, and does not recommend repeat doses in pregnancy unless other protective measures are unavailable.^4,10

The sources checked do not name nasal iodine or Lugol's solution. That is not a finding either way, so ask your doctor or pharmacist.

Who should ask a doctor before taking iodine in pregnancy?

Anyone with a thyroid condition or on thyroid medicine, because iodine can push thyroid function in either direction.²
Anyone thinking about kelp, seaweed or an iodine-only product on top of a prenatal vitamin.⁶
Anyone who takes lithium or an antithyroid medicine, which the potassium iodide label says can add to iodide's effect on the thyroid.⁴
Anyone who has had an allergic reaction to iodine, which the label lists as a reason not to use potassium iodide.⁴

Ask your doctor about iodine, and bring the Supplement Facts panel of your prenatal vitamin so the amounts can be added up.

Questions people ask

Is iodine supplement safe during pregnancy?

NIH lists a higher iodine need in pregnancy and an upper limit of 1,100 mcg a day for adults. A Cochrane review found too few data to judge routine supplements. Ask your doctor how your prenatal vitamin and diet already add up.^2,3

Is topical iodine safe during pregnancy?

The labels read for this page do not address pregnancy. LactMed says iodine is minimally absorbed through intact adult skin but can be absorbed in large amounts through wounds, mucous membranes or vaginal use. Ask your doctor or pharmacist.^8,9

Is povidone iodine safe during pregnancy?

An over-the-counter povidone iodine label says to stop use and ask a doctor if the condition persists or gets worse, and does not mention pregnancy. Ask your doctor or pharmacist before using it on large areas, wounds or inside the body.⁷

Is nasal iodine safe during pregnancy?

The sources checked do not address nasal iodine in pregnancy. LactMed notes only that iodine has not been measured in breastmilk after povidone-iodine nasal spray. That is not a finding either way, so ask your doctor or pharmacist.⁸

Is Lugol's iodine safe in pregnancy?

Lugol's solution is not named in the sources checked. A prescription potassium iodide solution carries a label warning of fetal harm, abnormal thyroid function and goiter in pregnancy. Ask your doctor before using any strong iodine solution.⁴

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.