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.

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    • "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). "
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