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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
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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)
Keywords
pregnancy; hypothyroidism; iodine supplementation; neonatal TSH; ioduria
About this articleTitle
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
Issue
Article type
Original paper
Pages
367-374
Published online
2016-07-05
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2117
Article views/downloads
2874
DOI
Pubmed
Bibliographic record
Endokrynol Pol 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
