Iodine need is increased during pregnancy and its deficiency can lead to complications in mother and fetus. The latest international guidelines have recommended a higher intake of iodine. Iran has implemented a national salt iodization program since 25 years ago, and the general population is iodine-sufficient. However, recent studies have shown that a significant proportion of pregnant women have urinary iodine concentration (UIC) below the recommended range of 150 - 250 µg/L. Based on the

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... lts of these studies, iodine supplement during pregnancy is widely used, but this practice is controversial. Objectives: The aim of this study was to evaluate the necessity for iodine supplementation in pregnant women living in Shiraz, an iodine-replete area. Methods: In this cross-sectional case-control study, UIC and thyroid-stimulating hormone of 174 pregnant women taking 150 µg/day iodine (group 1) were compared with 124 pregnant women not taking the supplement (group 2). The proportion of women with UIC below the recommended level in each group was also determined. UIC of the women in different trimesters in each group was also investigated and compared. Results: Mean UIC in groups 1 and 2 was 175.71 ± 56.43 µg/Land 122.5 ± 44.37 µg/L and this difference was significant (P = 0.006). Also, 56% of women in group 2 and 24 % in group 1 had UIC below the recommended value (P < 0.01). Mean UIC in both groups decreased with advancing gestational age. In group 1, mean UIC remained in the recommended range, whereas in group 2, it decreased to less than 100 µg/L. Conclusions: In areas covered by the national salt iodine implementation program, it is necessary to recommend iodine supplement to pregnant women to prevent iodine insufficiency.