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Need for Iodine Supplementation During Pregnancy

Last Updated: · Doctors
Authors

Question

About 3 years ago, I asked this thyroid manager whether it thought that hypothyroid women with autoimmune thyroid disease receiving levothyroxine (in treatment during pregnancy with increased doses of levothyroxine from the very beginning of pregnancy) should receive iodine supplements or not. At the time I was worried about the risk of a prolonged Wolff-Chaikoff in patients with Autoimmune thyroids, particularly during the first months of pregnancy. The expert answered that hypothyroid patients in treatment with levothyroxine should NOT received iodine supplementation during pregnancy. I then asked whether they should at least receive iodine during the third trimester, for the fetal thyroid, and was not answered. Has the position changed? Would it be a good idea to try out iodine supplementation for several weeks pre-conception if possible, and maitain it if hypothyoridism is not worsened? In other patients either on levothyroxine pre-pregnancy or with AI disease who start levothyroxine suplementation during early pregnancy, shouldn’t iodine supllemenation at least be assured to cover fetal thyroid needs in the second half of gestation? After all, T4 is a NOT that great a source of iodine. Of course, during breat feeding the case for iodine supllementation is clear. Help me out here. Thank you in advance.

Isabelle Runkle de la Vega. MD, PhD.
Hospital Clinico Universitario San Carlos/Madrid, Spain.

Response

  1. Pregnant women who are hypothyroid due toHashimoto’s thyroiditis and who, therefore, receive replacement therapy with L-thyroxine do not need to receive additional iodine supplements for themselves, since their endogenous thyroid function is replaced by thyroxine administration. However, the fetal thyroid gland needs iodine (especially – but not only – in the second half of gestation). Some of it will be provided by the natural iodine intake of the mother (in Spain, this is usually anywhere between 75 and 150 microgr/day) and some will also be provided from deiodination ofthe L-T4 taken by the mother. I guess that those were the main arguments underlying the answer you mentioned to have received 3years ago,indicating that no iodine supplementation was needed in such circumstances.
  2. Pregnant women with autoimmune thyroiditis (AITD) who DO NOT receive L-thyroxine before (or even during) pregnancy or who only receivesmall daily doses (say < 75 microgr/day) are obviouslyable to maintain a certain degree of endogenous thyroid function, depending on the severity of thier disease. In such circumstances, you may wish to provide additional iodine to the mother (and to the fetus, via her). The amount required to fortifyiodine nutrition will be in the order of 100-150 microgr/day. Such relatively moderate amounts of iodine DO NOT RISK toprovoke Wolff-Chaikoff effects, even in patients with AITD. There is therefore no reason that I can foresee not to give the mother and the fetus the potential benefits of having an adequate iodine intake during gestation. Finally, iodine supplementation in such cases could be implemented in the early stages of gestation and (why not?) already before conception.

Professor Daniel Glinoer
University of Brussels