Iodine requirements are increased during pregnancy, predominantly caused by an increase in renal iodide clearance and in the use of iodine for thyroid hormone production. Because iodine deficiency (ID) in pregnancy may be associated with neurodevelopmental deficits in the offspring, a pertinent question is at what level of iodine intake pregnant women should be advised to take iodine-containing supplements. The consensus reached by the WHO/UNICEF/ICCIDD in 2007 was that pregnant women should not be recommended to take iodine-containing supplements if the population in general had been iodine sufficient for at least 2 years. However, guidance on this differs between scientific societies. This review discusses iodine supplementation in pregnancy. Based on current evidence, the recommendations given by WHO/UNICEF/ICCIDD in 2007 provide a valid guidance on the use of iodine supplements in pregnant women. Women living in a population with a median urinary iodine concentration (UIC) at or above 100 µg/l are not in need of iodine supplementation in pregnancy. On the other hand, if the population median UIC is below 100 µg/l, pregnant women should take iodine-containing supplements until the population in general has been iodine sufficient for at least 2 years by way of universal salt iodization.

Keywords:
Urinary iodine concentration, Thyroid, Iodine supplement, Pregnancy
1.
Lazarus JH: The importance of iodine in public health. Environ Geochem Health 2015;37:605-618.
2.
Pearce EN, Andersson M, Zimmermann MB: Global iodine nutrition: where do we stand in 2013? Thyroid 2013;23:523-528.
3.
Andersen SL: Iodine status in pregnant and breastfeeding women: a Danish regional investigation. Dan Med J 2015;62:B5074.
4.
Zimmermann MB, Gizak M, Abbott K, Andersson M, Lazarus JH: Iodine deficiency in pregnant women in Europe. Lancet Diabetes Endocrinol 2015;3:672-674.
5.
WHO, UNICEF, ICCIDD: Assessment of Iodine Deficiency Disorders and Monitoring Their Elimination: A Guide for Programme Managers. Geneva, WHO, 2007.
6.
Aboul-Khair SA, Crooks J, Turnbull AC, Hytten FE: The physiological changes in thyroid function during pregnancy. Clin Sci 1964;27:195-207.
7.
Burrow GN, Fisher DA, Larsen PR: Maternal and fetal thyroid function. N Engl J Med 1994;331:1072-1078.
8.
Roti E, Fang SL, Green K, Emerson CH, Braverman LE: Human placenta is an active site of thyroxine and 3,3′5-triiodothyronine tyrosyl ring deiodination. J Clin Endocrinol Metab 1981;53:498-501.
9.
Mortimer RH, Galligan JP, Cannell GR, Addison RS, Roberts MS: Maternal to fetal thyroxine transmission in the human term placenta is limited by inner ring deiodination. J Clin Endocrinol Metab 1996;81:2247-2249.
10.
Chan S, Kachilele S, Hobbs E, Bulmer JN, Boelaert K, McCabe CJ, Driver PM, Bradwell AR, Kester M, Visser TJ, Franklyn JA, Kilby MD: Placental iodothyronine deiodinase expression in normal and growth-restricted human pregnancies. J Clin Endocrinol Metab 2003;88:4488-4495.
11.
Laurberg P, Andersen SL, Pedersen IB, Andersen S, Carle A: Screening for overt thyroid disease in early pregnancy may be preferable to searching for small aberrations in thyroid function tests. Clin Endocrinol 2013;79:297-304.
12.
Weeke J, Dybkjaer L, Granlie K, Eskjaer Jensen S, Kjaerulff E, Laurberg P, Magnusson B: A longitudinal study of serum TSH, and total and free iodothyronines during normal pregnancy. Acta Endocrinol 1982;101:531-537.
13.
Burns R, O'Herlihy C, Smyth PP: The placenta as a compensatory iodine storage organ. Thyroid 2011;21:541-546.
14.
Delange F, Dalhem A, Bourdoux P, Lagasse R, Glinoer D, Fisher DA, Walfish PG, Ermans AM: Increased risk of primary hypothyroidism in preterm infants. J Pediatr 1984;105:462-469.
15.
Thorpe-Beeston JG, Nicolaides KH, Felton CV, Butler J, McGregor AM: Maturation of the secretion of thyroid hormone and thyroid-stimulating hormone in the fetus. N Engl J Med 1991;324:532-536.
16.
Andersen SL, Sørensen LK, Krejbjerg A, Møller M, Laurberg P: Challenges in the evaluation of urinary iodine status in pregnancy: the importance of iodine supplement intake and time of sampling. Eur Thyroid J 2014;3:179-188.
17.
Vejbjerg P, Knudsen N, Perrild H, Laurberg P, Andersen S, Rasmussen LB, Ovesen L, Jorgensen T: Estimation of iodine intake from various urinary iodine measurements in population studies. Thyroid 2009;19:1281-1286.
18.
Keating FR, Power MH, Berkson J, Haines SF: The urinary excretion of radioiodine in various thyroid states. J Clin Invest 1947;26:1138-1151.
19.
Wong EM, Sullivan KM, Perrine CG, Rogers LM, Pena-Rosas JP: Comparison of median urinary iodine concentration as an indicator of iodine status among pregnant women, school-age children, and nonpregnant women. Food Nutr Bull 2011;32:206-212.
20.
Gowachirapant S, Winichagoon P, Wyss L, Tong B, Baumgartner J, Melse-Boonstra A, Zimmermann MB: Urinary iodine concentrations indicate iodine deficiency in pregnant Thai women but iodine sufficiency in their school-aged children. J Nutr 2009;139:1169-1172.
21.
Jaiswal N, Melse-Boonstra A, Sharma SK, Srinivasan K, Zimmermann MB: The iodized salt programme in Bangalore, India provides adequate iodine intakes in pregnant women and more-than-adequate iodine intakes in their children. Public Health Nutr 2015;18:403-413.
22.
Kung AW: Iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency. Public Health Nutr 2007;10:1600-1601.
23.
Raverot V, Bournaud C, Sassolas G, Orgiazzi J, Claustrat F, Gaucherand P, Mellier G, Claustrat B, Borson-Chazot F, Zimmermann M: Pregnant French women living in the Lyon area are iodine deficient and have elevated serum thyroglobulin concentrations. Thyroid 2012;22:522-528.
24.
Caldwell KL, Pan Y, Mortensen ME, Makhmudov A, Merrill L, Moye J: Iodine status in pregnant women in the National Children's Study and in U.S. women (15-44 years), National Health and Nutrition Examination Survey 2005-2010. Thyroid 2013;23:927-937.
25.
Bath SC, Furmidge-Owen VL, Redman CW, Rayman MP: Gestational changes in iodine status in a cohort study of pregnant women from the United Kingdom: season as an effect modifier. Am J Clin Nutr 2015;101:1180-1187.
26.
Wei Z, Wang W, Zhang J, Zhang X, Jin L, Yu X: Urinary iodine level and its determinants in pregnant women of Shanghai, China. Br J Nutr 2015;113:1427-1432.
27.
Smyth PP, Hetherton AM, Smith DF, Radcliff M, O'Herlihy C: Maternal iodine status and thyroid volume during pregnancy: correlation with neonatal iodine intake. J Clin Endocrinol Metab 1997;82:2840-2843.
28.
Ainy E, Ordookhani A, Hedayati M, Azizi F: Assessment of intertrimester and seasonal variations of urinary iodine concentration during pregnancy in an iodine-replete area. Clin Endocrinol 2007;67:577-581.
29.
Stilwell G, Reynolds PJ, Parameswaran V, Blizzard L, Greenaway TM, Burgess JR: The influence of gestational stage on urinary iodine excretion in pregnancy. J Clin Endocrinol Metab 2008;93:1737-1742.
30.
Anaforoglu I, Algun E, Incecayir O, Topbas M, Erdogan MF: Iodine status among pregnant women after mandatory salt iodisation. Br J Nutr 2016;115:405-410.
31.
Pedersen KM, Laurberg P, Iversen E, Knudsen PR, Gregersen HE, Rasmussen OS, Larsen KR, Eriksen GM, Johannesen PL: Amelioration of some pregnancy-associated variations in thyroid function by iodine supplementation. J Clin Endocrinol Metab 1993;77:1078-1083.
32.
Rezvanian H, Aminorroaya A, Majlesi M, Amini A, Hekmatnia A, Kachoie A, Amini M, Emami J: Thyroid size and iodine intake in iodine-repleted pregnant women in Isfahan, Iran. Endocr Pract 2002;8:23-28.
33.
Andersson M, Aeberli I, Wust N, Piacenza AM, Bucher T, Henschen I, Haldimann M, Zimmermann MB: The Swiss iodized salt program provides adequate iodine for school children and pregnant women, but weaning infants not receiving iodine-containing complementary foods as well as their mothers are iodine deficient. J Clin Endocrinol Metab 2010;95:5217-5224.
34.
Garcia-Solis P, Solis-S JC, Garcia-Gaytan AC, Reyes-Mendoza VA, Robles-Osorio L, Hernandez-Montiel HL, Leo-Amador GE: Iodine nutrition status in pregnant women in Mexico. Thyroid 2011;21:1367-1371.
35.
Pettigrew-Porter A, Skeaff S, Gray A, Thomson C, Croxson M: Are pregnant women in New Zealand iodine deficient? A cross-sectional survey. Aust NZ J Obstet Gynaecol 2011;51:464-467.
36.
Rose G: The Strategy of Preventive Medicine. New York, Oxford University Press 1992.
37.
Andersen SL, Sorensen LK, Krejbjerg A, Moller M, Laurberg P: Iodine deficiency in Danish pregnant women. Dan Med J 2013;60:A4657.
38.
Martin JC, Savige GS, Mitchell EK: Health knowledge and iodine intake in pregnancy. Aust NZ J Obstet Gynaecol 2014;54:312-316.
39.
WHO Secretariat, Andersson M, de Benoist B, Delange F, Zupan J: Prevention and control of iodine deficiency in pregnant and lactating women and in children less than 2-years-old: conclusions and recommendations of the Technical Consultation. Public Health Nutr 2007;10:1606-1611.
40.
Becker DV, Braverman LE, Delange F, Dunn JT, Franklyn JA, Hollowell JG, Lamm SH, Mitchell ML, Pearce E, Robbins J, Rovet JF: Iodine supplementation for pregnancy and lactation - United States and Canada: recommendations of the American Thyroid Association. Thyroid 2006;16:949-951.
41.
Caldwell KL, Miller GA, Wang RY, Jain RB, Jones RL: Iodine status of the U.S. population, National Health and Nutrition Examination Survey 2003-2004. Thyroid 2008;18:1207-1214.
42.
Caldwell KL, Makhmudov A, Ely E, Jones RL, Wang RY: Iodine status of the U.S. population, National Health and Nutrition Examination Survey, 2005-2006 and 2007-2008. Thyroid 2011;21:419-427.
43.
Stagnaro-Green A, Dogo-Isonaige E, Pearce EN, Spencer C, Gaba ND: Marginal iodine status and high rate of subclinical hypothyroidism in Washington DC women planning conception. Thyroid 2015;25:1151-1154.
44.
Lazarus J, Brown RS, Daumerie C, Hubalewska-Dydejczyk A, Negro R, Vaidya B: 2014 European Thyroid Association guidelines for the management of subclinical hypothyroidism in pregnancy and in children. Eur Thyroid J 2014;3:76-94.
45.
Abalovich M, Amino N, Barbour LA, Cobin RH, De Groot LJ, Glinoer D, Mandel SJ, Stagnaro-Green A: Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2007;92:S1-S47.
46.
De Groot L, Abalovich M, Alexander EK, Amino N, Barbour L, Cobin RH, Eastman CJ, Lazarus JH, Luton D, Mandel SJ, Mestman J, Rovet J, Sullivan S: Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2012;97:2543-2565.
47.
Pharoah PO, Buttfield IH, Hetzel BS: Neurological damage to the fetus resulting from severe iodine deficiency during pregnancy. Lancet 1971;1:308-310.
48.
Delange F, Ermans AM, Vis HL, Stanbury JB: Endemic cretinism in Idjwi Island (Kivu Lake, Republic of Congo). J Clin Endocrinol Metab 1972;34:1059-1066.
49.
Hynes KL, Otahal P, Hay I, Burgess JR: Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort. J Clin Endocrinol Metab 2013;98:1954-1962.
50.
Bath SC, Steer CD, Golding J, Emmett P, Rayman MP: Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet 2013;382:331-337.
51.
Vermiglio F, Lo Presti VP, Moleti M, Sidoti M, Tortorella G, Scaffidi G, Castagna MG, Mattina F, Violi MA, Crisa A, Artemisia A, Trimarchi F: Attention deficit and hyperactivity disorders in the offspring of mothers exposed to mild-moderate iodine deficiency: a possible novel iodine deficiency disorder in developed countries. J Clin Endocrinol Metab 2004;89:6054-6060.
52.
Morreale de Escobar G, Obregon MJ, Escobar del Rey F: Is neuropsychological development related to maternal hypothyroidism or to maternal hypothyroxinemia? J Clin Endocrinol Metab 2000;85:3975-3987.
53.
Silva JE, Silva S: Interrelationships among serum thyroxine, triiodothyronine, reverse triiodothyronine, and thyroid-stimulating hormone in iodine-deficient pregnant women and their offspring: effects of iodine supplementation. J Clin Endocrinol Metab 1981;52:671-677.
54.
Shi X, Han C, Li C, Mao J, Wang W, Xie X, Li C, Xu B, Meng T, Du J, Zhang S, Gao Z, Zhang X, Fan C, Shan Z, Teng W: Optimal and safe upper limits of iodine intake for early pregnancy in iodine-sufficient regions: a cross-sectional study of 7,190 pregnant women in China. J Clin Endocrinol Metab 2015;100:1630-1638.
55.
Glinoer D, De Nayer P, Delange F, Lemone M, Toppet V, Spehl M, Grun JP, Kinthaert J, Lejeune B: A randomized trial for the treatment of mild iodine deficiency during pregnancy: maternal and neonatal effects. J Clin Endocrinol Metab 1995;80:258-269.
56.
Taylor PN, Okosieme OE, Dayan CM, Lazarus JH: Therapy of endocrine disease: impact of iodine supplementation in mild-to-moderate iodine deficiency: systematic review and meta-analysis. Eur J Endocrinol 2013;170:R1-R15.
57.
Lazarus JH, Bestwick JP, Channon S, Paradice R, Maina A, Rees R, Chiusano E, John R, Guaraldo V, George LM, Perona M, Dall'Amico D, Parkes AB, Joomun M, Wald NJ: Antenatal thyroid screening and childhood cognitive function. N Engl J Med 2012;366:493-501.
58.
Taylor PN, Okosieme OE, Murphy R, Hales C, Chiusano E, Maina A, Joomun M, Bestwick JP, Smyth P, Paradice R, Channon S, Braverman LE, Dayan CM, Lazarus JH, Pearce EN: Maternal perchlorate levels in women with borderline thyroid function during pregnancy and the cognitive development of their offspring: data from the Controlled Antenatal Thyroid Study. J Clin Endocrinol Metab 2014;99:4291-4298.
59.
Hales C, Channon S, Taylor PN, Draman MS, Muller I, Lazarus J, Paradice R, Rees A, Shillabeer D, Gregory JW, Dayan CM, Ludgate M: The second wave of the Controlled Antenatal Thyroid Screening (CATS II) study: the cognitive assessment protocol. BMC Endocr Disord 2014;14:95.
60.
Wolff J, Chaikoff IL: Plasma inorganic iodide as a homeostatic regulator of thyroid function. J Biol Chem 1948;174:555-564.
61.
Eng PH, Cardona GR, Fang SL, Previti M, Alex S, Carrasco N, Chin WW, Braverman LE: Escape from the acute Wolff-Chaikoff effect is associated with a decrease in thyroid sodium/iodide symporter messenger ribonucleic acid and protein. Endocrinology 1999;140:3404-3410.
62.
Laurberg P, Cerqueira C, Ovesen L, Rasmussen LB, Perrild H, Andersen S, Pedersen IB, Carle A: Iodine intake as a determinant of thyroid disorders in populations. Best Pract Res Clin Endocrinol Metab 2010;24:13-27.
63.
Karmisholt J, Laurberg P: Serum TSH and serum thyroid peroxidase antibody fluctuate in parallel and high urinary iodine excretion predicts subsequent thyroid failure in a 1-year study of patients with untreated subclinical hypothyroidism. Eur J Endocrinol 2008;158:209-215.
64.
Bjergved L, Jorgensen T, Perrild H, Carle A, Cerqueira C, Krejbjerg A, Laurberg P, Ovesen L, Bulow Pedersen I, Banke RL, Knudsen N: Predictors of change in serum TSH after iodine fortification: an 11-year follow-up to the DanThyr study. J Clin Endocrinol Metab 2012;97:4022-4029.
65.
Pedersen IB, Knudsen N, Carle A, Vejbjerg P, Jorgensen T, Perrild H, Ovesen L, Rasmussen LB, Laurberg P: A cautious iodization programme bringing iodine intake to a low recommended level is associated with an increase in the prevalence of thyroid autoantibodies in the population. Clin Endocrinol 2011;75:120-126.
66.
Brantsaeter AL, Abel MH, Haugen M, Meltzer HM: Risk of suboptimal iodine intake in pregnant Norwegian women. Nutrients 2013;5:424-440.
67.
Bath SC, Walter A, Taylor A, Wright J, Rayman MP: Iodine deficiency in pregnant women living in the South East of the UK: the influence of diet and nutritional supplements on iodine status. Br J Nutr 2014;111:1622-1631.
68.
Rasmussen LB, Ovesen L, Bulow I, Jorgensen T, Knudsen N, Laurberg P, Pertild H: Dietary iodine intake and urinary iodine excretion in a Danish population: effect of geography, supplements and food choice. Br J Nutr 2002;87:61-69.
69.
Laurberg P, Nohr SB, Pedersen KM, Fuglsang E: Iodine nutrition in breast-fed infants is impaired by maternal smoking. J Clin Endocrinol Metab 2004;89:181-187.
70.
Andersen SL, Nohr SB, Wu CS, Olsen J, Pedersen KM, Laurberg P: Thyroglobulin in smoking mothers and their newborns at delivery suggests autoregulation of placental iodide transport overcoming thiocyanate inhibition. Eur J Endocrinol 2013;168:723-731.
© 2016 European Thyroid Association Published by S. Karger AG, Basel
2016
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.