Assessing iodine intakes in pregnancy and strategies for improvement

An adequate intake of iodine in the diet of pregnant women is important to ensure normal growth and development of the fetus. It is difficult, however, to accurately determine iodine intakes using traditional methods of dietary assessment, primarily because the contribution of iodised salt use, at the table and in cooking, to total iodine intake is difficult to quantify. Given the limitations of dietary assessment, biochemical indices in blood and urine are typically used to assess iodine status in children and adults. Although reference ranges exist for thyroid hormones, there has been no consensus on the cut-offs needed in pregnancy to diagnose iodine deficiency. In contrast, a median urinary iodine concentration (UIC) of 150–249 μg/L has been established to determine the adequate iodine status of a group of pregnant women. However, the large intra-individual variation in UIC from either spot or 24 h urine samples means that UIC cannot be used to assess iodine status in an individual pregnant woman. The difficulty in determining if an individual pregnant woman is iodine deficient is problematic for cross-sectional studies examining associations between iodine status in pregnancy and developmental outcomes in the child.