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

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 Suplementacja jodowa u ciężarnych z niedoczynnością tarczycy leczonych L-tyroksyną nie wpływa na stężenia TSH noworodków ani nie zapobiega obniżeniu stężeń wolnych hormonów tarczycy u matek w drugim i trzecim trymestrze AbstractIntroduction: 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 10 th gestational week. Primary outcomes were the maternal thyroid function tests (TSH, fT4, fT3) and neonatal TSH concentrations at the 3-4 th 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 deficiency and real-life supplementation ineffectiveness in Polish pregnant women and its impact on thyroid metabolism

“…In comparison with the former method, inductively coupled plasma mass spectrometry (ICP-MS), HPLC-UV is less complicated and does not require any advanced equipment. Compared with the spectrophotometric method, using the Sandell-Kolthoff reaction (S-K), HPLC-UV does not involve the ingestion of the initial material, or the use of noxious substances (arsenic and cerium) (19,37). Moreover, HPLC-UV provides better selectivity of the analytes to be determined in such a complex biological matrix as urine.…”

“…Both serum samples were stored frozen in −20°C. Ioduria, as UIC, was measured using a validated ion-pair high-performance liquid chromatography with ultraviolet detection (HPLC-UV), as described (19). Creatinine was determined in the same urine sample by a colorimetric enzyme-linked immunosorbent assay (ELISA) detection kit (ThermoFisher, EIACUN, Frederick, USA).…”

An update: maternal iodine supplementation, thyroid function tests, and child neurodevelopmental outcomes

“…Iodine sources for the fetus include food, maternal endogenous thyroid hormone, or levothyroxine tablets. Patients being treated for hyperthyroidism or taking levothyroxine in preconception and pregnancy do not require iodine supplementation [2,24]. Mothers who are breastfeeding have increased daily iodine requirements as iodine is secreted into breast milk [25].…”