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.
abstract: BACKGROUND
  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.
  
  
  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 &gt; 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).
authors.affiliation: Department of Endocrinology, Centre of Postgraduate Medical Education, Bielanski Hospital, Warsaw, Poland. hjastrzebska@cmkp.edu.pl.
authors.forename: Helena
authors.initials: H
authors.lastname: Jastrzębska
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kochman
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Bartoszewicz
authors.forename: Mariusz
authors.initials: M
authors.lastname: Ołtarzewski
authors.forename: Romuald
authors.initials: R
authors.lastname: Dębski
authors.forename: Wojciech
authors.initials: W
authors.lastname: Zgliczyński
mesh_terms: D000328:Adult; D019587:Dietary Supplements; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy*; D007231:Infant, Newborn; D007455:Iodine / Q000494:pharmacology / Q000627:therapeutic use*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000188:drug therapy*; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D013960:Thyroid Function Tests; D013974:Thyroxine / Q000627:therapeutic use*
chemical_list: D007455:Iodine; D013974:Thyroxine
keywords: hypothyroidism; iodine supplementation; ioduria; neonatal TSH; pregnancy