A randomized, double-blind study of iodine supplementation during pregnancy in Sweden: pilot evaluation of maternal iodine status and thyroid function

Purpose Pregnant women in Sweden are mildly iodine deficient. We investigated the effect of daily iodine supplementation on the iodine and thyroid status of pregnant women. Methods In this pilot, randomized, double-blind trial, 200 thyroid-healthy pregnant women were recruited at mean (standard deviation) pregnancy week 8.85 (1.62) and assigned (1:1) to daily intake of a multivitamin tablet with or without 150 mu g of iodine. Urine and serum samples were collected at baseline and once during the second and third trimesters. Urinary iodine concentration (UIC), serum thyroglobulin (Tg), thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid peroxidase antibodies (TPOabs) were analyzed. Neonatal TSH data were collected. UIC and Tg were also analyzed in a group of 89 thyroid-healthy non-pregnant women of reproductive age (WRA). Results At baseline, the intervention and the control groups had similar median UIC (interquartile range (IQR)): 110 mu g/L (74-119) and 111 mu g/L (66-168), respectively. The intervention group reached iodine sufficiency with median UIC (IQR) 139 mu g/L (89-234) and 136 mu g/L (91-211) in the second and third trimester, respectively, without significant difference from the lower limit of the recommended range, i.e. 150-250 mu g/L (p = 0.42 and p = 0.87, respectively). The intervention group had higher median UIC and lower median Tg compared to the control group during the second (p < 0.001 and p = 0.019, respectively) and third trimester (p < 0.001 and p = 0.003, respectively), whereas thyroid hormones, serum TPOabs, and neonatal TSH were similar. The WRA group presented median UIC (IQR) 65 mu g/L (30-98) and median Tg (IQR) 18 mu g/L (13-27). Conclusion A daily supplement containing 150 mu g of iodine to a group of pregnant women with mild iodine deficiency improved the iodine status from mild ID to iodine sufficiency. This improvement seems to have had a positive impact on maternal thyroglobulin. This study is now under extension to investigate the children's neuropsychological development.

Automated summary

Daily supplementation with 150 μg of iodine improved the iodine status of pregnant women in Sweden from mild deficiency to sufficiency. This improvement had a positive impact on maternal thyroglobulin levels. The study is now being extended to investigate the neuropsychological development of children.