A majority of prenatal vitamins in the US do not match the stated amount on the labels.

According to US researchers, since most of the supplements contain less iodine than what is stated on the label, they are putting the newborns at a developmental risk. Iodine is critically important for the developing fetus.

"Iodine nutrition is critically important in pregnancy," explained Dr. Elizabeth Pearce, co-author of the letter and an assistant professor of medicine at Boston University Medical Center. "Women who are deficient in pregnancy have children often with lower IQs or neurocognitive delays. Iodine deficiency is the leading cause of preventable mental retardation in the world."

The American Thyroid Association's recommends 150 micrograms per day as the daily dose for pregnant and lactating women.

But surprisingly, of the 44 products that claimed to deliver that amount, one third had less than half that amount.

Doctors at Boston University Medical Center tested the iodine content of 60 multivitamins with iodine. It was found that only 28 percent contained the amount stated on the label.

Iodine deficiency affects more than 38 percent of the world's population and is the leading cause of preventable mental retardation.