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.

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).

Iodine status of pregnant women from central Poland ten years after introduction of iodine prophylaxis programme.

INTRODUCTION: Until 1997, Poland was one of the European countries suffering from mild/moderate iodine deficiency. In 1997, a national iodine prophylaxis programme was implemented based on mandatory iodisation of household salt with 30 ± 10 mg KI/kg salt, obligatory iodisation of neonatal formula with 10 µg KI/100 mL and voluntary supplementation of pregnant and breast-feeding women with additional 100-150 µg of iodine. Our aim in this study was to evaluate the iodine status of pregnant women ten years after iodine prophylaxis was introduced. MATERIAL AND METHODS: A cross-sectional study was undertaken in 100 healthy pregnant women between the fifth and the 38th week of gestation with normal thyroid function, singleton pregnancy, normal course of gestation, without drugs known to influence thyroid function except iodine. Serum TSH, fT(4), fT(3), thyroglobulin (TG), anti-peroxidase antibodies (TPO-Ab), anti-thyroglobulin antibodies (TGAb) and urinary iodine concentration (UIC) were determined. Thyroid volume and structure were evaluated by ultrasonography. RESULTS: Fifty nine per cent of studied pregnant women had a diet rich with iodine carriers and 35% obtained iodine supplements. Twenty eight per cent appeared to have a goitre: 11 diffuse and 17 a nodular one, median goitre volume was 18.7 mL (range 6.8-29.0 mL). Median UIC was 112.6 µg/L (range 36.3-290.3 µg/L), only 28% of women had UIC ≥ 150 µg/L. Median UIC was significantly higher in the group receiving iodine supplements than in the group without iodine supplements: 146.9 µg/L v. 97.3 µg/L respectively, p 〈 0.001. Serum TSH, fT(3) and fT(3)/fT(4) molar ratio increased significantly during pregnancy while fT(4) declined. Median serum TG was normal: 18.3 ng/mL (range 0.4-300.0 ng/mL) and did not differ between trimesters. Neonatal TSH performed on the third day of life as a neonatal screening test for hypothyroidism was normal in each case: median value was 1.49 mIU/L (range 0.01-7.2 mIU/L). Less than 3% (2 out of 68) of results were 〉 5 mIU/L. CONCLUSION: Iodine supplements with 150 µg of iodine should be prescribed for each healthy pregnant woman according to the assumptions of Polish iodine prophylaxis programme to obtain adequate iodine supply. (Pol J Endocrinol 2010; 61 (6): 646-651).