Pregnant women should take prenatal vitamins that contain iodine, a U.S. medical journal suggests.

Iodine deficiency in pregnancy can lead to problems including goiter in both the mother and fetus, pregnancy loss, infant mortality and intellectual impairments.

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It is time for all prenatal vitamins to contain iodine, U.S. doctors say. (iStock)

In Wednesday's issue of the Journal of the American Medical Association, doctors in the U.S. noted that urine tests results suggest that mild iodine deficiency occurs in at least a subset of pregnant women in the U.S.

Half of prenatal vitamin brands sold in the U.S. contain no iodine and it's estimated that 80 per cent of pregnant women in the U.S. don't use supplements containing the nutrient, Dr. Elizabeth Pearce of Boston University School of Medicine and her co-authors said.

They suggested that medical groups work with pharmaceutical and vitamin manufacturers to ensure all prenatal multivitamins contain 150 micrograms of potassium iodine as thyroid and endocrinology groups advocate.

"In the interim, clinicians should recommend only those prenatal vitamins that contain iodine. The path seems clear. It is time for all prenatal vitamins to contain iodine."

Pearce also recommends that prenatal multivitamins sold in Canada contain iodine.

But less is known about the dietary iodine status of pregnant Canadian women compared with women in the U.S., Pearce said in an email.

Overall, iodine levels in urine indicated a mild deficiency in 22 per cent of Canadians aged three to 79 and a moderate deficiency in seven per cent, Statistics Canada reported this year. About 15 per cent had an excessive intake.

For pregnant women, Pearce earlier found sufficient iodine concentrations among 142 mainly Caucasian, well educated and relatively affluent pregnant women from the Toronto area.