Women attempting pregnancy may experience difficulty or delays in conceiving when they have moderate or severe iodine deficiency, according to findings published in Human Reproduction.

“Iodine deficiency is common in many parts of the world, including the United States and parts of Europe,” James L. Mills, PhD, of the epidemiology branch, division of intramural population health research at Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, told Endocrine Today. “Our results show that there is a significant delay in how long it takes women who are iodine deficient to become pregnant.”

Mills and colleagues evaluated data from the Longitudinal Investigation of Fertility and the Environment (LIFE) study on 467 women (median age, 29 years) attempting to become pregnant who had sufficient urine samples available for iodine analysis to determine whether urinary iodine status is associated with time required to become pregnant. Participants discontinued contraception within 2 months to become pregnant between 2005 and 2009. At enrollment, urine samples were collected for iodine analysis.

During the 12-month study period, 71% of participants became pregnant, 10% did not and 19% withdrew or were lost to follow-up.

Most participants had sufficient urinary iodine concentrations ( 100 µg/L; 55.7%) followed by mildly deficient (50-99 µg/L; 21.8%), moderately deficient (20-49 µg/L; 20.8%) and severely deficient (< 20 µg/L; 1.7%); median iodine concentrationswere 112.8 µg/L among all participants, 114.1 µg/L in those who became pregnant, 97.2 µg/L in those who did not become pregnant and 113.6 µg/L in those who withdrew.

Participants who did not become pregnant were more likely to have iodine concentrations in the moderately or severely deficient range compared with those who became pregnant (29.8% vs. 21.4%), but the difference did not meet statistical significance. The time to get pregnant was longer in participants with iodine-to-creatinine ratios less than 50 µg/g vs. those with ratios of at least 100 µg/g (P = .028). Fecundity was reduced by 46% in participants with iodine-to-creatinine ratios less than 50 µg/g vs. those with ratios of at least 100 µg/g (fecundity OR = 0.54; 95% CI, 0.31-0.94).

“Our data suggest that women who have iodine deficiency may have problems getting pregnant,” Mills said. “Because iodine requirements increase during pregnancy, initially to supply the fetus with thyroid hormone and later to provide iodine for the fetal thyroid, it is important for women attempting to become pregnant to have sufficient iodine stores. Therefore, women attempting to become pregnant should be sure that they have sufficient iodine intake.” – by Amber Cox