open access

Vol 67, No 4 (2016)
Original papers
Published online: 2016-07-05
Submitted: 2015-10-11
Accepted: 2016-02-05
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Iodine supplementation during pregnancy of hypothyroid women treated with L-thyroxine neither influences neonatal TSH nor prevents decrease in maternal free thyroid hormone concentrations in second and third trimesters

Helena Jastrzębska, Magdalena Kochman, Zbigniew Bartoszewicz, Mariusz Ołtarzewski, Romuald Dębski, Wojciech Zgliczyński
DOI: 10.5603/EP.a2016.0049
·
Endokrynologia Polska 2016;67(4):367-374.

open access

Vol 67, No 4 (2016)
Original papers
Published online: 2016-07-05
Submitted: 2015-10-11
Accepted: 2016-02-05

Abstract

Introduction: Pregnant women require about 250 μg of iodine daily. Hypothyroid women treated with L-thyroxine do not utilise iodine, and metabolism of L-thyroxine tablets is an additional source of iodine for their foetuses. The aim of the study was to evaluate the influence of iodine supplementation in hypothyroid pregnant women treated with L-thyroxine on neonate TSH concentration and maternal thyroid parameters.

Material and methods: Ninety-two pregnant women with primary hypothyroidism on adequate thyroid hormone replacement were voluntarily divided into two groups: “thyroxine” (n = 38) treated with L-thyroxine only, and “thyroxine + iodine” (n = 54) treated additionally with 150 μg/day of iodine since 10th gestational week. Primary outcomes were the maternal thyroid function tests (TSH, fT4, fT3) and neonatal TSH concentrations at the 3–4th day of life. Urinary iodine concentration was measured at first and third trimester to compare iodine status in both groups.

Results: Iodine supplementation significantly increased median urinary ioduria in the third trimester (from 95.15 μg/L to 151.50 μg/L), but did not prevent the decrease of maternal fT4 and fT3 concentrations in the second and third trimester. Median neonate TSH concentration in both groups was within normal range, but was 33% higher in the “thyroxine + iodine” than in the “thyroxine” group (1.91 mU/L vs. 1.34 mU/L). Moreover, 8.77% of newborns in the “thyroxine + iodine” group had TSH > 5 mIU/L.

Conclusions: We did not find evidence for a positive influence of iodine supplementation on thyroid function of either hypothyroid pregnant women sufficiently treated with L-thyroxine or their neonates. (Endokrynol Pol 2016; 67 (4): 367–374)

Abstract

Introduction: Pregnant women require about 250 μg of iodine daily. Hypothyroid women treated with L-thyroxine do not utilise iodine, and metabolism of L-thyroxine tablets is an additional source of iodine for their foetuses. The aim of the study was to evaluate the influence of iodine supplementation in hypothyroid pregnant women treated with L-thyroxine on neonate TSH concentration and maternal thyroid parameters.

Material and methods: Ninety-two pregnant women with primary hypothyroidism on adequate thyroid hormone replacement were voluntarily divided into two groups: “thyroxine” (n = 38) treated with L-thyroxine only, and “thyroxine + iodine” (n = 54) treated additionally with 150 μg/day of iodine since 10th gestational week. Primary outcomes were the maternal thyroid function tests (TSH, fT4, fT3) and neonatal TSH concentrations at the 3–4th day of life. Urinary iodine concentration was measured at first and third trimester to compare iodine status in both groups.

Results: Iodine supplementation significantly increased median urinary ioduria in the third trimester (from 95.15 μg/L to 151.50 μg/L), but did not prevent the decrease of maternal fT4 and fT3 concentrations in the second and third trimester. Median neonate TSH concentration in both groups was within normal range, but was 33% higher in the “thyroxine + iodine” than in the “thyroxine” group (1.91 mU/L vs. 1.34 mU/L). Moreover, 8.77% of newborns in the “thyroxine + iodine” group had TSH > 5 mIU/L.

Conclusions: We did not find evidence for a positive influence of iodine supplementation on thyroid function of either hypothyroid pregnant women sufficiently treated with L-thyroxine or their neonates. (Endokrynol Pol 2016; 67 (4): 367–374)

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Keywords

pregnancy; hypothyroidism; iodine supplementation; neonatal TSH; ioduria

About this article
Title

Iodine supplementation during pregnancy of hypothyroid women treated with L-thyroxine neither influences neonatal TSH nor prevents decrease in maternal free thyroid hormone concentrations in second and third trimesters

Journal

Endokrynologia Polska

Issue

Vol 67, No 4 (2016)

Pages

367-374

Published online

2016-07-05

DOI

10.5603/EP.a2016.0049

Bibliographic record

Endokrynologia Polska 2016;67(4):367-374.

Keywords

pregnancy
hypothyroidism
iodine supplementation
neonatal TSH
ioduria

Authors

Helena Jastrzębska
Magdalena Kochman
Zbigniew Bartoszewicz
Mariusz Ołtarzewski
Romuald Dębski
Wojciech Zgliczyński

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