Comparison of median urinary iodine concentration as an indicator of iodine status among pregnant women, school-age children, and nonpregnant women

Background. Most surveys that assess the iodine status of populations target school-age children, whereas others may target nonpregnant women with the assumption that the iodine status of these groups is representative of other groups in the same population. Objective. To assess whether the median urinary iodine concentration (UIC) of school-age children or nonpregnant women can be used to accurately represent the iodine status of pregnant women. Methods. Using the World Health Organization Vitamin and Mineral Nutrition Information System and a literature review, we identified urinary iodine surveys that included pregnant women and school-age children and/or nonpregnant women in the same location and year using estimates from the smallest geographic level to increase the number of data points. Linear regression was used to assess the relationships between the median UIC for the comparisons. Results. There were 48 survey pairs with pregnant women and school-age children (total sample sizes of 8,622 and 16,844, respectively), and 26 pairs with pregnant and nonpregnant women (sample sizes of 3,222 and 5,520, respectively). The country contributing the most data points was China. When the median UIC in school-age children or nonpregnant women indicated iodine intake was adequate or above requirements, approximately half the time pregnant women had inadequate iodine intake. Conclusions. Adequate iodine nutrition status of school-age children or nonpregnant women may not indicate adequate iodine nutrition status among pregnant women. In order to assess the iodine status of pregnant women, the iodine status would need to be assessed in this group.