Optimal Assessment and Quantification of Iodine Nutrition in Pregnancy and Lactation: Laboratory and Clinical Methods, Controversies and Future Directions
Westmead Clinical School, Faculty of Medicine and Health, The University of Sydney, Sydney 2006, Australia
Australian Centre for Control of Iodine Deficiency Disorders (ACCIDD), Faculty of Medicine and Health, The University of Sydney, Sydney 2006, Australia
School of Medicine (Pathology), Liverpool Hospital Clinical School, Western Sydney University, Liverpool, Sydney 2170, Australia
School of Public Health, Faculty of Medicine and Health, The University of Sydney, Sydney 2006, Australia
Author to whom correspondence should be addressed.
Nutrients 2019, 11(10), 2378; https://doi.org/10.3390/nu11102378
Received: 1 August 2019 / Revised: 5 September 2019 / Accepted: 15 September 2019 / Published: 5 October 2019
(This article belongs to the Special Issue The Assessment and Prevention of Gestational Iodine Deficiency and Its Adverse Fetal Consequences: A Focus on Mild Iodine Deficiency)
Iodine intake must be boosted during pregnancy to meet the demands for increased production and placental transfer of thyroid hormone essential for optimal foetal development. Failure to meet this challenge results in irreversible brain damage, manifested in severity from neurological cretinism to minor or subtle deficits of intelligence and behavioural disorders. Attention is now being focused on explaining observational studies of an association between insufficient iodine intake during pregnancy and mild degrees of intellectual impairment in the offspring and confirming a cause and effect relationship with impaired maternal thyroid function. The current qualitative categorisation of iodine deficiency into mild, moderate and severe by the measurement of the median urinary iodine concentration (MUIC) in a population of school-age children, as a proxy measure of dietary iodine intake, is inappropriate for defining the degree or severity of gestational iodine deficiency and needs to be replaced. This review examines progress in analytical techniques for the measurement of urinary iodine concentration and the application of this technology to epidemiological studies of iodine deficiency with a focus on gestational iodine deficiency. We recommend that more precise definitions and measurements of gestational iodine deficiency, beyond a spot UIC, need to be developed. We review the evidence for hypothyroxinaemia as the cause of intrauterine foetal brain damage in gestational iodine deficiency and discuss the many unanswered questions, from which we propose that further clinical studies need to be designed to address the pathogenesis of neurodevelopmental impairments in the foetus and infant. Agreement on the testing instruments and standardization of processes and procedures for Intelligence Quotient (IQ) and psychomotor tests needs to be reached by investigators, so that valid comparisons can be made among studies of gestational iodine deficiency and neurocognitive outcomes. Finally, the timing, safety and the efficacy of prophylactic iodine supplementation for pregnant and lactating women needs to be established and confirmation that excess intake of iodine during pregnancy is to be avoided.