Parameters of Thyroid Function Throughout and After Pregnancy in an Iodine-Deficient Population

Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal.
Thyroid: official journal of the American Thyroid Association (Impact Factor: 4.49). 09/2010; 20(9):995-1001. DOI: 10.1089/thy.2009.0356
Source: PubMed


The thyroid hormone milieu is of crucial importance for the developing fetus. Pregnancy induces physiological changes in thyroid homeostasis that are influenced by the iodine status. However, longitudinal studies addressing thyroid function during pregnancy and after delivery are still lacking in mild-to-moderate iodine-deficient populations. Here we characterize the serum parameters of thyroid function throughout pregnancy, and until 1 year after delivery, in a population of pregnant women whom we have previously reported to be iodine deficient (median urinary iodine levels below 75 microg/L).
One hundred eighteen pregnant women were studied. Clinical data were recorded and serum was collected. Serum total and free thyroxine (T(4)) and triiodothyronine (T(3)), thyroid-stimulating hormone, thyroxine-binding globulin, and thyroglobulin were measured.
Mean total T(4) ranged from 159 at the start of gestation to 127 nmol/L at 1 year after delivery, free T(4) from 14.2 to 17.8 pmol/L, total T(3) from 2.4 to 2.1 nmol/L, free T(3) from 6.7 pmol/L to 6.4 pmol/L, thyroid-stimulating hormone from 1.2 to 1.4 mIU/L, T(4)-binding globulin from 62.0 to 26.9 mg/L, and thyroglobulin from 11 to 10 microg/L.
The pregnant women in this study had an absence of the usual free T(4) spike and a smaller than expected increment in total T(4), described during pregnancy in iodine-sufficient populations. A greater number of women had subclinical hypothyroidism compared with iodine-sufficient populations. This hormonal profile, most likely due to iodine insufficiency, may result in inadequate thyroid hormone supply to the developing fetus. We conclude that care should be taken when reviewing the results of thyroid hormone tests in iodine-insufficient populations and when no gestation-specific reference values have been established. In addition, we recommend iodine supplementation in our population and populations with similar iodine status, particularly during pregnancy and lactation.

Download full-text


Available from: Pedro Oliveira, Oct 06, 2015
49 Reads
  • Source
    • "Model predictions of serum T4 for varying iodide intake rates in pregnant women were compared to values reported in the study of Silva and Silva (1981), which investigated the effects of varying iodide intake on serum thyroid hormone levels in 250 pregnant women from an iodine-deficient area of Santiago, Chile. To evaluate the modelpredicted levels for maternal fT4 and T3, data from several published studies were used representing populations of pregnant women in several countries (Costeira et al., 2010; Moleti et al., 2011; Soldin et al., 2007; Vermiglio et al., 1999). The iodide intake rates in these studies generally ranged from 60 to 200 μg/day, although one population (Vermiglio et al., 1999) included moderately iodine-deficient women (mean urinary iodide excrete rates of 46.1 μg/day). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Ensuring adequate iodine intake is important, particularly among women of reproductive age, because iodine is necessary for early life development. Biologically based dose-response modeling of the relationships among iodide status, perchlorate dose, and thyroid hormone production in pregnant women has indicated that iodide intake has a profound effect on the likelihood that exposure to goitrogens will produce hypothyroxinemia. We evaluated the possibility of increasing iodine intake to offset potential risks from perchlorate exposure. We also explored the effect of dietary exposures to nitrate and thiocyanate on iodine uptake and thyroid hormone production. Our modeling indicates that the level of thyroid hormone perturbation associated with perchlorate exposures in the range of current regulatory limits is extremely small and would be overwhelmed by other goitrogen exposures. Our analysis also shows that microgram levels of iodine supplementation would be sufficient to prevent the goitrogenic effects of perchlorate exposure at current regulatory limits among at risk individuals. The human health risks from supplementing drinking water with iodine are negligible; therefore, this approach is worthy of regulatory consideration. Copyright © 2015. Published by Elsevier Ltd.
    Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association 03/2015; 80. DOI:10.1016/j.fct.2015.03.014 · 2.90 Impact Factor
  • Source
    • "This study warrants the need for establishment of gestationspecific reference intervals for thyroid related hormone to describe thyroid hormone deficiency in pregnant women [7] [26]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Problem Statement. Thyroid gland in women undergoes functional changes during pregnancy. A few studies have described such changes in pregnant women residing in iodine deficient areas. Objective. To document these changes in pregnant women residing in Lahore, a low iodine intake urban area of Pakistan. Patients and Methods. In 254 pregnant women, data of FT4, FT3, and TSH during the first and subsequent trimesters were obtained and compared with those of 110 nonpregnant women. These hormones were determined in serum by radioimmunoassay (RIA) techniques using commercial kits. Results. Compared to nonpregnant women mean FT4 level was decreased, and FT3 and TSH increased significantly (P < 0.05) in pregnant women. A negative correlation of FT4 with TSH was observed in all three trimesters. Serum FT3 was positively correlated with TSH only during the third trimester. As a function of gestation time, FT4 levels progressively decreased, and FT3 and TSH levels increased significantly (one-way ANOVA F = 108.2, 17.3, and 44.8, resp.; all P < 0.05) exhibiting thyroid gland adaptations. Conclusion. Pregnancy is associated with significant alterations in thyroid function due to low iodine intake in women residing in study area. The compensated thyroid function poses a risk of thyroid failure in a number of pregnant women.
    10/2013; 2013(2):234031. DOI:10.1155/2013/234031
  • Source
    • "Pregnant women have physiological modifications in the regulation of thyroid function. Changes in the peripheral metabolism of thyroid hormones have been described, mainly, increases in thyroxine-binding globulin (TBG), in human chorionic gonadotropin (HCG) which acts on the thyrotropin (TSH) receptors, and in renal filtration which leads to a greater loss of iodine [4]. To cope with these changes and the stress of pregnancy, women must have optimal thyroid function and an adequate iodine intake. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Iodine is an essential trace element for the synthesis of thyroid hormones, which are keys in maternal metabolism during pregnancy as well as in neurological development during fetal and postnatal life. This was a prospective study on iodine status and thyroid function in women during pregnancy in the Basque country to assess whether there was any relationship among maternal urinary iodine, maternal thyroid function and thyrotropin (TSH) in newborns, and to explore any difference in women experiencing miscarriages. We analyzed TSH, free T4 (FT4), free T3 (FT3), thyroid peroxidase antibody (TPO-Ab) titers in serum and urinary iodine concentrations (UIC) in 2104 women in the first trimester of pregnancy and in 1322 of them in their second trimester. We obtained neonatal TSH levels in 1868 cases. In the first (T1) and second trimesters (T2), the median UICs were 88.5μg/L and 140μg/L, respectively. No relationship was found between UIC and FT4, or maternal and neonatal TSH. In T1 and T2, 9.7% and 7.5% of women were TPO-Ab positive, respectively. The total miscarriage rate was 10%. The percentage of miscarriages in healthy women was 8.9%, lower than in women with overt hypothyroidism (21.2%; p<0.001) and than in women with subclinical hypothyroidism (15.6%; p<0.025). The miscarriage rate was not higher in TPO-Ab-positive women. In this study most women had iodine deficiency during pregnancy. Neonatal TSH is not correlated with maternal UIC during pregnancy. Pregnant women with hypothyroidism have a higher rate of miscarriages.
    Journal of Trace Elements in Medicine and Biology 07/2013; 27(4). DOI:10.1016/j.jtemb.2013.07.002 · 2.37 Impact Factor
Show more