Iodine supplementation in pregnancy – is it time?

Abstract

Iodine is essential for the synthesis of thyroid hormone and optimal foetal neurological development. Pregnant women living in borderline or moderate-severe iodine deficient areas are at particularly high risk of being iodine deficient, and this may have important clinical consequences, particularly for the neurocognitive development of the offspring. It is a substantial problem and many countries including the United Kingdom are mild-moderately iodine deficient. Although the detrimental effects of severe iodine deficiency are well recognized, the benefits of correcting mild-to-moderate iodine deficiency are unclear due to a lack of randomized controlled trials in this area. However, observational data increasingly indicate that there may be substantial health and economic benefits from correcting iodine deficiency in pregnancy. There is now a growing trend from learned societies that iodine supplementation should be utilized in pregnancy in countries with mild-to-moderate iodine deficiency. The dose of iodine supplement needs to reflect local iodine status and iodization policies and will need careful monitoring at the population level to ensure doses to prevent under/excess dosing which would undermine the potential benefits. National tailored guidance is therefore essential.

Iodine deficiency amongst pregnant women in South-West England

“…A recent systematic review has shown that iodine supplementation during pregnancy in mild‐to‐moderate iodine deficiency is associated with improvement in maternal thyroid function as well as reduction in maternal thyroid volume even though evidence from randomized controlled trials to show that this also improves offspring's cognitive development is still lacking . However, potential health and economic benefits of iodine supplementation in pregnant women living in mild‐to‐moderate iodine deficient countries outweigh potential harms . There is no national guidance on the use of iodine supplement in pregnancy in the UK; however, several national and international authorities recommend between 150 and 200 μg of iodine supplement daily for pregnant and lactating women living in mild‐to‐moderate iodine deficient countries to meet the WHO guidelines.…”

“…14 However, potential health and economic benefits of iodine supplementation in pregnant women living in mild-to-moderate iodine deficient countries outweigh potential harms. [15][16][17] There is no national guidance on the use of iodine supplement in pregnancy in the UK; however, several national and international authorities [18][19][20] recommend between 150 and 200 lg of iodine supplement daily for pregnant and lactating women living in mild-to-moderate iodine deficient countries to meet the WHO guidelines. In our study, only 35% of pregnant women reported taking iodine-containing prenatal vitamins.…”

Benign thyroid disease in pregnancy: A state of the art review

“…It is nowadays accepted that severe maternal iodine deficiency can have adverse implications for the mother, including hypothyroidism and goitre; for the foetus, including miscarriage and stillbirth; for the neonate, including neonatal mortality; and for the child, including impaired neurological development, faltering growth and cretinism [10] , [11] , [12] . Iodine supplementation is recommended as a treatment of maternal hypothyroidism in severely iodine deficient populations and there is good evidence that it improves clinical outcomes including cretinism and infant mortality rates [11] , [13] .…”

“…On the other hand, excessive iodine supplementation should be avoided. There is evidence that over-replacement with iodine could increase the risk of subclinical hypothyroidism, isolated hypothyroxinaemia and auto-immune hypothyroidism [13] , [25] . Furthermore, kelp supplements should be avoided due to their variable, and sometimes excessive, iodine content [14] .…”

Preconception management of thyroid dysfunction

“…Pregnant women with sufficient iodine nutrition are able to seamlessly implement these adaptive mechanisms, but in iodine‐deficient states, these changes may fail to deliver adequate thyroid hormones to the foetus. Population iodine nutrition remains highly variable, and even in countries with iodine‐sufficient status, some pregnant women do not achieve the minimum recommended daily iodine intake of 250 mcg daily . European and American endocrine society guidelines recommend antenatal supplementation of 150 mcg of iodine daily, but specific recommendations in the UK are lacking …”