The Relationship Between Iodine Excess and Thyroid Function During Pregnancy and Infantile Neurodevelopment at 18-24 Months

Background: Thyroid disease is a prevalent condition during pregnancy, and excessive iodine intake can lead to changes in thyroid function. However, research on the relationship between maternal iodine excess, thyroid hormones during pregnancy, and infantile neurodevelopment is limited. Objectives: This study aimed to explore the relationship between maternal iodine excess and thyroid hormones during pregnancy and infantile neurodevelopment. The objective was to provide evidence to support and enhance the prevention of neurodevelopmental retardation in infants. Methods: From 2016 to 2018, a prospective study was conducted from pregnancy to 18-24 mo postpartum. Maternal urinary iodine concentration (UIC), thyroid-stimulating hormone (TSH), total serum iodine (TSI), and nonprotein-bound serum iodine during pregnancy were determined. The Gesell Development Scale was used to assess neurodevelopment of infants aged 18-24 mo. The iodine status of pregnant females was divided into following 4 groups on the basis of the distribution of maternal UIC: <100 mu g/L (moderate deficiency), 100-149 mu g/L (mild deficiency), 150-249 mu g/L (sufficiency), and >250 mu g/L (above requirement). Results: Our study included 469 mother-infant pairs. Compared with the maternal UIC of 150-249 mu g/L during pregnancy, risk of adaptive developmental delay was increased in infants with maternal UIC >= 250 mu g/L (OR: 2.38; 95% CI: 1.06, 5.35). Pregnant females with TSI >90th quantiles were more likely to have offspring with language developmental delay than those with lower TSI in 10th-90th quantiles (OR: 3.06; 95% CI: 1.09, 8.58). Risk of fine motor developmental delay was increased in infants with maternal TSH >= 2.5 mIU/L during pregnancy (OR: 4.32; 95% CI: 1.43, 13.0). Conclusions: Maternal iodine nutritional status above requirement (UIC >= 250 mu g/L or TSI >90th quantiles) during pregnancy negatively affects infantile neurodevelopment. Maternal TSH >= 2.5 mIU/L during pregnancy was an independent risk factor for infantile neurodevelopment. This trial was registered at clinicaltrials.gov as NCT03710148.