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NIH Record - 75th Anniversary - National Institutes of Health

Iodine Deficiency May Reduce Pregnancy Chances

Woman smiling, holding pregnancy test results with man smiling over her shoulder

Findings suggest that women who are thinking of becoming pregnant may need more iodine.

Photo: ThinkStock

Women with moderate to severe iodine deficiency may take longer to achieve a pregnancy, compared to women with normal iodine levels, according to a study by researchers at NIH. The study is the first to investigate the potential effects of mild to moderate iodine deficiency—common among women in the United States and the United Kingdom—on the ability to become pregnant. It appears in the latest edition of Human Reproduction.

Iodine is a mineral used by the body to regulate metabolism. It also helps regulate bone growth and brain development in children. It is found in seafood, iodized salt, dairy products and some fruits and vegetables. Severe iodine deficiency has long been known to cause intellectual and developmental delays in infants.

“Our findings suggest that women who are thinking of becoming pregnant may need more iodine,” said Dr. James Mills, who conducted the study along with colleagues at NICHD and the New York State department of health in Albany. “Iodine requirements increase during pregnancy and the fetus depends on this mineral to make thyroid hormone and to ensure normal brain development.”

The researchers analyzed data collected from 501 U.S. couples who were planning pregnancy from 2005 to 2009. The couples were part of the Longitudinal Investigation of Fertility and the Environment (LIFE) study, which sought to examine the relationship between fertility, lifestyle and environmental exposures. When the women enrolled in the study, they provided a urine sample from which their iodine levels were measured. Each woman was also given a digital, at-home pregnancy test.

Of the 467 women analyzed for the current study, iodine status was sufficient in 260 (55.7 percent), mildly deficient in 102 (21.8 percent), moderately deficient in 97 (20.8 percent) and severely deficient in 8 (1.7 percent).

Although the study population was not a representative sample of the U.S. population, the authors note that the percentage of women in the study having insufficient iodine (44.3 percent) is close to that seen in population-wide studies. For example, a previous study estimated that 30 percent of U.S. women of childbearing age had insufficient levels of iodine. 

The authors concluded that if their findings are confirmed, public health officials in countries where iodine deficiency is common may want to consider programs to increase iodine intake in women of child-bearing age. 

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