An update: maternal iodine supplementation, thyroid function tests, and child neurodevelopmental outcomes

Abstract

Purpose of review The impact of maternal iodine supplementation (MIS) during pregnancy on thyroid function and child neurodevelopmental outcomes in areas of mild-to-moderate iodine deficiency (MMID) remains unclear. Recent findings Despite growing success of salt iodization programs, a 2022 meta-analysis found that 53% of pregnant patients worldwide continue to have insufficient iodine intake during pregnancy. A 2021 randomized controlled trial (RCT) found that MIS in women with mild iodine deficiency led to iodine sufficiency and positive effects on maternal thyroglobulin. A 2021 cohort study of MIS initiated prior to pregnancy was associated with lower thyroid-stimulating hormone (TSH), higher FT3, and FT4. Other cohort studies, however, found that neither salt iodization nor MIS were adequate to meet pregnancy iodine needs. Data have been mixed regarding maternal iodine status and pregnancy outcomes in patients of MMID. Meta-analyses have not shown any clear benefit on infant neurocognitive outcomes with MIS of MMID patients. A 2023 meta-analysis found that the prevalence of excess iodine intake in pregnancy was 52%. Summary MMID continues to exist during pregnancy. Salt iodization alone may be insufficient to ensure adequate iodine status during pregnancy. There is an absence of high-quality data to support routine MIS in areas of MMID. However, patients with specialized diets (vegan, nondairy, no seafood, noniodized salt, and so on) may be at risk for inadequate iodine status in pregnancy. Excess iodine intake can be detrimental to the fetus and should be avoided during pregnancy.

Maternal Urinary Iodine Concentration during Pregnancy and Its Impact on Child Growth and Neurodevelopment: An 11-Year Follow-Up Study

“…Mild-to-moderate iodine deficiency during pregnancy has been associated with adverse child neurodevelopmental outcomes in some [9][10][11][12][13][14] but not all studies [15][16][17][18][19][20][21]. In addition, intervention trials have not convincingly shown a beneficial effect of iodine supplementation during pregnancy on child development in regions of mild-to-moderate iodine deficiency [22,23]. These discrepancies may be related to differences in the studied populations or in the methods used to assess iodine status or child development, including available data on confounders [24].…”

“…In contrast, no associations with maternal UIC were found in a Spanish study cohort of 12-to 30-month-olds [15,16], a Dutch study cohort of 6-year-olds [17], a Norwegian study cohort of 8-year-olds [18], an Australian study cohort of 18-month-olds [19], a British study cohort of 4-to 7-year-olds [20], or a Bangladeshi study cohort of 5-to 10-year-olds [21]. In addition, iodine supplementation trials in pregnancy have mostly failed to demonstrate a beneficial effect on child development in regions of mild-to-moderate iodine deficiency [22,23]. The inconsistency in results may be attributed to differences in methods for assessing iodine and child development, severity of the iodine deficiency in the population, and adjustment for potential confounding variables [24].…”