In pregnancy, the increased synthesis of thyroid hormones, essential for optimal foetal neurodevelopment, increases iodine requirements. The adverse effects of severe maternal iodine deficiency in pregnancy on foetal brain development are well established, but the effects of milder deficiency have, until more recently, been less certain.

Iodine deficiency is the largest preventable cause of brain damage and mental impairment worldwide.¹ Australia was identified as a country with mild iodine deficiency in the Australian National Iodine Nutrition Study of 2003–2004.² To address the re-emergence of iodine deficiency in Australia, the government introduced mandatory iodine fortification of salt used in bread in 2009.³ However, FSANZ openly admits that the mandatory iodine fortification policy is inadequate for high-risk groups with increased requirements, such as pregnant and lactating women, stating that they may still not be adequately protected.⁴ Even now, more than 50% of children and pregnant or breastfeeding women living in Australia have been shown to be iodine deficient, and are at risk of developing thyroid disease.⁵

There is a growing body of evidence that links milder forms of thyroid dysfunction to adverse pregnancy outcomes, suggesting that there may be important effects of mild or moderate maternal iodine deficiency on foetal development.^6-9 For example, a study comparing the Intelligent Quotient (IQ) scores of seven to nine year old children of mothers with subclinical hypothyroidism (SCH) during pregnancy versus the scores of healthy controls, found that the children from hypothyroid mothers had IQ scores seven points lower than controls.¹⁰ In addition, results of a 2018 meta-analysis showed that SCH is significantly associated with delayed intellectual and motor development, low birth weight, premature delivery, foetal distress and foetal growth restriction.¹¹

Insufficient iodine status in pregnancy is a public health concern and healthcare practitioners play a vital role in providing patients with evidence-based recommendations.  As it is difficult for pregnant and breastfeeding women to get enough iodine through food alone, women planning a pregnancy, and pregnant and lactating women are advised to take an iodine supplement.^12,13

• Preconception: Supplementation of 150 mcg iodine per day for at least 4 weeks prior to conception.¹²
• Pregnancy: 220 mcg of iodine per day.¹⁴
• Lactation: 270 mcg of iodine per day.¹⁴
• Caution: women with pre-existing thyroid disease should exercise caution and seek medical advice before taking any supplement. The safe upper level of intake during both pregnancy and lactation is 1,100 mcg/day for adult women.

Preventing mild-to-moderate iodine deficiency in pregnant women by securing adequate iodine status before conception is the optimal strategy to counteract the detrimental effects of inadequate iodine intake on maternal thyroid health and the subsequent reduced physical and intellectual potential of the offspring.⁸

 

References

1. Charlton, K., Y. Probst, and G. Kiene, Dietary Iodine Intake of the Australian Population after Introduction of a Mandatory Iodine Fortification Programme. Nutrients, 2016. 8(11): p. 701.
2. Li, M., et al., Are Australian children iodine deficient? Results of the Australian National Iodine Nutrition Study. Med J Aust, 2006. 184(4): p. 165-9.
3. Food Standards Australia New Zealand. Proposal P1003 - Mandatory Iodine Fortification for Australia. 2008.
4. Gallego, G., S. Goodall, and C.J. Eastman, Iodine deficiency in Australia: is iodine supplementation for pregnant and lactating women warranted? Med J Aust, 2010. 192(8): p. 461-3.
5. The Australian Thyroid Foundation. Iodine deficiency and nutrition. 2018; Available from: https://www.thyroidfoundation.org.au/Iodine-Deficiency.
6. Robinson, S.M., et al., Preconception Maternal Iodine Status Is Positively Associated with IQ but Not with Measures of Executive Function in Childhood. J Nutr, 2018. 148(6): p. 959-966.
7. Korevaar, T.I.M., et al., Thyroid disease in pregnancy: new insights in diagnosis and clinical management. Nat Rev Endocrinol, 2017. 13(10): p. 610-622.
8. Markhus, M.W., et al., Maternal Iodine Status is Associated with Offspring Language Skills in Infancy and Toddlerhood. Nutrients, 2018. 10(9).
9. Zimmermann, M.B., Iodine deficiency in pregnancy and the effects of maternal iodine supplementation on the offspring: a review. Am J Clin Nutr, 2009. 89(2): p. 668S-72S.
10. Haddow, J.E., et al., Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child. N Engl J Med, 1999. 341(8): p. 549-55.
11. Liu, Y., et al., The Association Between Maternal Subclinical Hypothyroidism and Growth, Development, and Childhood Intelligence: A Meta-analysis. Journal of clinical research in pediatric endocrinology, 2018. 10(2): p. 153-161.
12. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists. Pre-pregnancy Counselling. 2017.
13. NHMRC, Iodine supplementation for pregnant and breastfeeding women, NHMRC, Editor. 2010, Australian Government: Australia.
14. National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. 2006; Available from: http://www.nhmrc.gov.au.