Iodine Status, Thyroid Function, and Birthweight: A Complex Relationship in High-Risk Pregnancies

Abstract

(1) Background: The consequences of iodine deficiency and/or thyroid dysfunction during pregnancy have been extensively studied, emphasizing on infant neurodevelopment. However, the available information about the relationship between iodine, thyroid hormones, and fetal growth in high-risk pregnancies is limited. We aim to investigate if iodine metabolism and/or thyroid parameters can be affected by adverse antenatal/perinatal conditions. (2) Methods: A cross-sectional study examined differences in iodine status, thyroid function, and birthweight between high-risk (HR group; n = 108)) and low-risk pregnancies (LR group; n = 233) at the time of birth. Urinary iodine concentration (UIC), iodine levels in amniotic fluid, and thyroid parameters [thyroid-stimulating hormone (TSH), free thyroxine (FT4)] were measured in mother–baby pairs. (3) Results: There were significant differences between HR and LR groups, free thyroxine (FT4) concentration in cord blood was significantly higher in the LR group compared with HR pregnancies (17.06 pmol/L vs. 15.30 pmol/L, respectively; p < 0.001), meanwhile iodine concentration in amniotic fluid was significantly lower (13.11 µg/L vs. 19.65 µg/L, respectively; p < 0.001). (4) Conclusions: Our findings support the hypothesis that an adverse intrauterine environment can compromise the availability of FT4 in cord blood as well as the iodine metabolism in the fetus. These differences are more noticeable in preterm and/or small fetuses.

Characterization of Fetal Thyroid Levels at Delivery among Appalachian Infants

“…All thyroid parameters were higher in the low-risk pregnancy group besides free T4, which was similar between the low- and high-risk groups, with a positive correlation between maternal and neonatal thyroid hormone levels across the board. They concluded that an unfavorable environment in utero can limit the availability of free T4 in cord blood and limit fetal iodine metabolism, especially in small fetuses [ 29 ]. Due to the limited number of neonatal thyroid studies available, our study examined whether or not specific maternal demographics impacted neonatal thyroid hormone levels.…”

Potential Risk Factors for Isolated Hypothyroxinemia in Women of Childbearing Age—Results from Retrospective Analysis

“…The prevalence of IH was found to be higher in women with gestational diabetes mellitus in a moderately iodine-deficient area [17], and the association between low FT4 concentration and gestational diabetes mellitus in the first and the second trimester of pregnancy has been confirmed in a recently published meta-analysis [11]. Interestingly, FT4 concentration in cord blood was found to be higher in the low-risk pregnant patients compared to high-risk individuals [18]. The relationship between IH and adverse pregnancy outcomes has been recently summarized [19].…”

Effect of Iodine Nutrition Status on Thyroid Function and Pregnancy Outcomes

“…Despite that how maternal iodine nutrition status regulated fetal growth remained unsolved, the role of impaired placental function, which was closely related to the fetus development, was thoroughly emphasized [20,21]. A study on iodine status, thyroid function and birth weight indicated that iodine concentration in amniotic uid was negatively correlated with UIC and birth weight [22], suggesting that maternal iodine de ciency the intrauterine environment, which in turn indirectly affects fetal growth and development. Moreover, maternal iodine nutrition status affected the production of thyroid hormones, which provides the thyroid hormones required by the fetus in the rst trimester, regarded as an essential window of narrow variations in maternal thyroid parameters [23].…”