The mean gestational age at the time of urine collection was 23.7 weeks. The median urinary iodine concentration (UIC) was 78 μg/L (range 4-750 μg/L). A total of 676 (79%) of women had UICs less than 150 μg/L, which is the cutoff recommended by the World Health Organization for adequate iodine nutrition status in pregnant women in a population. A total of 242 (28%) women had UICs less the 50 μg/L, which indicates severe iodine deficiency. The median UIC was higher in 155 (18%) women who were taking iodine-containing supplements during pregnancy compared to those who were not taking iodine-containing supplements (92 μg/L vs. 77 μg/L, respectively).
Children of women with UICs < 100 μg/L had lower scores in language skills compared to children of women with UICs ≥ 100 μg/L. Mother’s UICs did not have significant association with children’s motor skills. Mother’s use of iodine-containing supplements was not associated with any benefit in children’s development up to 18 months of age.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In this study of mother-child pairs from Norway, low iodine levels in mothers below 100 μg/L in pregnancy was associated with lower language skills in children up to 18 months of age. Taking iodine-containing supplements later in pregnancy did not show any beneficial effects on children’s development.
Because there is increased need for iodine in pregnancy, pregnant women and their young children can be particularly sensitive to effects of iodine deficiency. This study supports need for adequate iodine nutrition in pregnant women. The American Thyroid Association currently recommends for women planning pregnancy, pregnant, or breastfeeding to take supplements containing 150 μg of iodine a day. Although taking iodine-containing supplements did not show beneficial effects in this study, it may be because the use of supplements were later in pregnancy in the second trimester. In addition, women who were taking iodine-containing supplements also had low urine iodine levels below 150 μg/L. Therefore, it would be important for pregnant women or women planning pregnancy to have adequate iodine nutrition before or early in pregnancy to prevent adverse effects on baby’s development.
— Sun Y. Lee, MD