Maternal thyroid function in different conditions of iodine nutrition in pregnant women exposed to mild-moderate iodine deficiency: an observational study

Abstract

The regular use of iodine-containing supplements proved effective in reducing the risk of inappropriately low FT4 levels during pregnancy. The observed TSH increase in 150-I women may be because of a transient stunning effect on the thyroid gland, occurring as a result of the abrupt increase in daily iodine intake. Whilst the importance of gestational iodine supplementation is undisputed, we believe that in mild-moderately ID areas, women considering conception should be advised to take iodine supplementation for several months prior to pregnancy.

Suboptimal Maternal Iodine Intake Is Associated with Impaired Child Neurodevelopment at 3 Years of Age in the Norwegian Mother and Child Cohort Study

“…Initiating supplement use during pregnancy might be too late and may also provide less iodine than needed to compensate for the effects of a depleted iodine store on thyroid function. A sudden increase in iodine intake, although modest and within the recommendations, might also lead to a ''stunning effect,'' with transient inhibition of maternal or fetal thyroid hormone production (50). In addition, because the iodine supplements reported by the women in MoBa were almost exclusively multisupplements, we cannot eliminate the possibility of other substances in the supplements acting as confounders or effect modifiers.…”

Iodine status during pregnancy in India and related neonatal and infant outcomes

“…There is substantial iodine storage as iodo-tyrosines in the thyroid, so consumption is not required daily. Iodine supplementation or food fortification can normalize TSH (27) , reduce endemic goitre and normalize thyroid metabolism (28,29) . Individual dietary requirements vary: non-pregnant adults have a mean requirement of 95 mg/d (30) .…”

Management of subclinical hypothyroidism in pregnancy: are we too simplistic?

“…Comparable to the above mentioned studies, a decrease in iodine availability -as anticipated by the increased renal clearance of iodine in pregnancy -may contribute to the decrease in maternal TSH levels in early pregnancy. This would explain some epidemiological data supporting a positive correlation between TSH level and urinary iodine concentration (16,27,28), but is contradicted in a large cross-sectional Chinese study conducted for measuring TSH and iodine excretion within the first trimester of pregnancy, showing that serum TSH concentrations did not differ in non-pregnant women during the first 6 weeks of pregnancy, but only between weeks 7 and 12 of pregnancy a significant decrease was found (11).…”

“…Placental production of human chorionic gonadotrophin (hCG) and a rise in oestrogen production that increases binding proteins, namely thyroxinebinding globulin affect free TH levels. TSH dips according to most but not all studies within the first trimester, whereas free TH concentrations decrease, albeit very slightly, mainly during the latter part of pregnancy (10,11,14,15,16,17,18,19). These observed alterations are not only due to pathophysiological changes but are, at least in part, due to methodological issues.…”