Iodine Deficiency/Excess and Pregnancy Outcomes Publisher



Nazeri P¹ ; Delshad H² Show Affiliations
Source: Thyroid Diseases in Pregnancy Published:2022

Abstract

Iodine is ingested in several chemical forms. Iodine is rapidly and nearly all absorbed (>90%) in the stomach and duodenum. Iodate, widely used in iodization of salt, is reduced in the gut and absorbed as iodide. The body of a healthy adult contains 15-20 mg of iodine, of which 70-80% is in the thyroid. Iodine is used by the thyroid gland to produce thyroid hormones. For women, iodine is necessary for optimal function of the reproductive system and for normal fetal growth and development. In chronic iodine deficiency, the iodine content of the thyroid might fall to less than 20 microgram. In iodine-sufficient areas, the adult thyroid traps about 60 microgram of iodine per day to balance losses and maintain synthesis of thyroid hormone. The sodium/iodide symporter (NIS) transfers iodine intake; in situations with adequate iodine supply, 10% or less of absorbed iodine is taken up by the thyroid. In chronic iodine deficiency, this percentage can exceed 80%. Iodine consists of 65% and 59% of the weights of thyroxine (T4) and tri-iodothyronine (T3), respectively. The released iodine enters the plasma iodine pool and can be taken up again by the thyroid or excreted by the kidney. More than 90% of ingested iodine is ultimately excreted in the urin. Despite significant progress has been achieved in elimination of iodine deficiency worldwide, vulnerable groups such as pregnant women, lactating mothers, and infants are still at risk of iodine deficiency. During pregnancy several major changes occur in thyroid physiology that result in higher iodine requirements in pregnant than non-pregnant women, which can be difficult to meet through diet; therefore, iodine supplementation for pregnant and those who are planning for pregnancy is necessary. The most serious adverse effect of iodine deficiency occurs to the fetus. It is well documented that severe iodine deficiency in utero and in early life can result in impaired mental function, poor school performance, and reduced intellectual ability. However, it is still uncertain whether mild-to-moderate maternal iodine deficiency may have a long-term negative impact on child neurodevelopment. Few studies to date have explored the effect of iodine excess on maternal and fetal outcomes. It has been shown that chronic excess iodine intake during pregnancy was associated with maternal hypothyroxinemia, which has been linked with preterm delivery and possibly irreversible childhood intelligence quotient. This chapter deals with the role of iodine and its metabolism during pregnancy. The most recent data on number of countries according to their iodine status in the general population as well as pregnant women are here reported. In addition, consequences of iodine deficiency and excess in pregnant women and fetuses and potential benefits of iodine supplementation in this critical period are discussed. © Springer Nature Switzerland AG 2022.