Evolving Concepts in Gestational Iodine Requirements

Iodine is an essential trace element for thyroid hormone synthesis, metabolic homeostasis, and fetal neurodevelopment. During pregnancy, maternal iodine requirements increase substantially, yet global recommendations are primarily based on population-level biomarkers rather than individualized physiological data. In this review, we examine current international guidelines for iodine adequacy in pregnancy, evaluate the limitations of population-based metrics—such as urinary iodine concentration (UIC) and serum thyroglobulin (Tg)—and highlight emerging evidence on physiological adaptations, functional biomarkers, and individualized risk factors. We incorporated data from population surveillance studies, mechanistic investigations of thyroid adaptation, and clinical outcome research identified through a literature search of PubMed/MEDLINE and Scopus (2016–2025). Evidence indicates that the widely adopted WHO range for iodine intake in pregnant women may overestimate the actual needs of gestation. There is a U-shaped relationship between iodine intake and thyroid outcomes, meaning both low and high iodine exposure adversely affect maternal thyroid function and fetal neurodevelopment, highlighting the narrow optimal intake window. Individualized considerations—including autoimmune thyroid disease, supplementation practices, environmental exposures, and coexisting micronutrient deficiencies—further modulate iodine requirements. Functional indices, such as the Thyroid Feedback Quantile-based Index (TFQI), may offer complementary tools for assessing iodine adequacy beyond traditional biomarkers.