Serum Thyroglobulin Concentration Is a Weak Marker of Iodine Status in a Pregnant Population with Iodine Deficiency

OBJECTIVE

To assess the reliability of thyroglobulin (Tg) as a marker of iodine status during pregnancy.

DESIGN

299 women aged 30.5 ± 4.8 years (mean ± SD) were studied.

METHODS

In every subject, we measured urinary iodine concentration (UIC), serum thyrotropin (TSH), Tg, free thyroxine (fT4), Tg autoantibodies (TgAbs) and human chorionic gonadotropin (hCG) levels. We excluded samples with increased TgAbs from the analysis.

RESULTS

According to WHO criteria, the study population was iodine deficient in every trimester. Serum Tg levels did not differ during the three trimesters of pregnancy. Serum hCG levels fell significantly as pregnancies advanced. A weak, significantly negative correlation (limited to the 3rd trimester) was found between Tg and UIC (ρ = -0.187, p = 0.039). Serum fT4 decreased as pregnancies advanced and TSH increased. Serum fT4 was negatively correlated with TSH (ρ = -0.161, p = 0.006) and positively with hCG (ρ = +0.165, p = 0.005). The multiple regression equation of Tg based on hCG, TSH, UIC and trimester of pregnancy was significant but weak (F = 4.057, p = 0.003; R(2) = 0.055), with hCG as a significant predictor Tg (p for log hCG = 0.041).

CONCLUSIONS

Tg cannot be considered as a valid marker of iodine deficiency in pregnancy, at least in a mildly iodine-deficient environment. Further studies in a larger patient cohort with differences in iodine status, as well as studies on Tg changes after improving iodine status in pregnant women, are needed in order to corroborate these results.

No increase in renal iodine excretion during pregnancy: a telling comparison between pregnant women and their spouses

OBJECTIVE

Adequate dietary iodine intake is necessary for normal thyroid gland function at all times, and most particularly during pregnancy. Increased iodine loss is cited, among other factors, as responsible for the increased iodine demand in this period. Our aim was to compare renal iodine excretion between women during all three pregnancy trimesters with that of their spouses and thereby to estimate the iodine intake in an a large sample of pregnant women in urban areas in Greece.

DESIGN

Four hundred twenty-four healthy pregnant women were included prospectively (residents of Athens n=218, residents of Patras n=206). The spouses of 177 of these women following the same diet were also studied. Determinations included serum FT4, TSH and aTPO and urinary iodine excretion (UIE).

RESULTS

No difference was found either in median UIE throughout pregnancy or between the UIE of the pregnant women and their spouses during the trimesters. Throughout pregnancy, mild iodine deficiency was noted and was classified as mild in 60%, moderate in 30% and severe in 10% of the women studied. Users of iodized salt had significantly higher median UIE compared with non-users. Serum FT4 levels decreased and TSH increased as pregnancy progressed.

CONCLUSIONS

Our study indicates that renal iodine excretion is not increased during pregnancy. This finding needs to be confirmed by further investigation in other populations with different iodine intakes. Thus, increased iodine requirements in pregnancy are possibly due to extra-renal causes. The population of pregnant women in Greek urban areas is mildly-and often moderately and severely-iodopenic and needs to be treated accordingly.