Iodine Deficiency in Pregnancy: The Effect on Neurodevelopment in the Child

Sheila Skeaff

doi:10.3390/nu3020265

Abstract

Iodine is an integral part of the thyroid hormones, thyroxine (T4) and tri-iodothyronine (T3), necessary for normal growth and development. An adequate supply of cerebral T3, generated in the fetal brain from maternal free T4 (fT4), is needed by the fetus for thyroid hormone dependent neurodevelopment, which begins in the second half of the first trimester of pregnancy. Around the beginning of the second trimester the fetal thyroid also begins to produce hormones but the reserves of the fetal gland are low, thus maternal thyroid hormones contribute to total fetal thyroid hormone concentrations until birth. In order for pregnant women to produce enough thyroid hormones to meet both her own and her baby’s requirements, a 50% increase in iodine intake is recommended. A lack of iodine in the diet may result in the mother becoming iodine deficient, and subsequently the fetus. In iodine deficiency, hypothyroxinemia (i.e., low maternal fT4) results in damage to the developing brain, which is further aggravated by hypothyroidism in the fetus. The most serious consequence of iodine deficiency is cretinism, characterised by profound mental retardation. There is unequivocal evidence that severe iodine deficiency in pregnancy impairs brain development in the child. However, only two intervention trials have assessed neurodevelopment in children of moderately iodine deficient mothers finding improved neurodevelopment in children of mothers supplemented earlier rather than later in pregnancy; both studies were not randomised and were uncontrolled. Thus, there is a need for well-designed trials to determine the effect of iodine supplementation in moderate to mildly iodine deficient pregnant women on neurodevelopment in the child.

Highlights

Despite considerable progress over the last 25 years, iodine deficiency is still one of the most common micronutrient deficiencies in the world today
A 50% increase in iodine intake is recommended in order for pregnant women to produce enough thyroid hormones to meet fetal requirements [4]
Severe iodine deficiency exists when more than 30% of children have goitre, the population has a median urinary iodine concentration (MUIC) < 20 μg/L, and pregnant women living in the area give birth to cretins

Summary

Introduction

Despite considerable progress over the last 25 years, iodine deficiency is still one of the most common micronutrient deficiencies in the world today. Of greatest concern is the effect of iodine deficiency on the developing brain. The most serious effect of iodine deficiency is cretinism, which occurs in women who are severely iodine deficient during pregnancy. Attention is turning to the adverse effects of moderate and mild iodine deficiency in pregnancy. Iodine deficiency in pregnancy will affect both the mother and the child, little attention has been paid to the consequences of iodine deficiency on maternal health. This review will describe the role iodine plays, via thyroid hormones, in the development of the brain from conception to birth and present evidence of the impact of severe, moderate, and mild iodine deficiency in pregnancy on neurodevelopment in the child

The Role of Thyroid Hormones in Fetal Brain Development

Determining the Severity of Iodine Deficiency in Pregnancy

Methods

Findings

Conclusion