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: 3.84). 09/2010; 20(9):995-1001. DOI: 10.1089/thy.2009.0356
Source: PubMed

ABSTRACT 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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    10/2013; 2013:234031. DOI:10.1155/2013/234031
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    Thyroid: official journal of the American Thyroid Association 04/2014; DOI:10.1089/thy.2014.0052 · 3.84 Impact Factor
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    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.
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