Iodine is an essential micronutrient that is required for thyroid hormone (TH) synthesis. However, adequate maternal thyroid function is critical for fetal growth and neurodevelopment. Pregnancy increases iodine requirements due to enhanced renal clearance, higher maternal TH production, and transplacental transfer, making pregnant women especially vulnerable to iodine deficiency. In this review, we examine the molecular mechanisms of TH synthesis and regulation, placental transport and metabolism, and the physiological adaptations of thyroid function during gestation. We also analyze the clinical and public health consequences of iodine imbalances, ranging from deficiency to excess. Evidence indicates that mild iodine deficiency—which is common even in developed countries—can lead to maternal thyroid overstimulation, increased thyroglobulin levels, altered T3/T4 ratios, and enlarged thyroid volume, while severe deficiency results in maternal and fetal hypothyroidism with irreversible neurocognitive impairment in the offspring. Conversely, excessive iodine intake may impair fetal thyroid function through mechanisms such as the Wolff–Chaikoff effect. In conclusion, ensuring balanced iodine intake through iodized salt, supplementation, and routine thyroid monitoring during pregnancy is essential to protect maternal health and optimize early neurodevelopment.

Iodine is a crucial component of thyroid hormones (THs), specifically triiodothyronine (T3) and thyroxine (T4) and is vital for normal thyroid function. During pregnancy, a deficiency in iodine can result in inadequate production of THs, leading to hypothyroidism. This con-dition can negatively impact the intellectual development of the newborn. Numerous stud-ies have demonstrated that iodine deficiency during pregnancy correlates with lower IQ levels in children. This deficiency can hinder critical processes such as neurogenesis, neu-ronal migration, and myelination, all of which are essential for proper cognitive develop-ment. Research indicates that children born to iodine-deficient mothers are at a higher risk of having lower IQs compared to those whose mothers received iodine supplements during pregnancy. Therefore, ensuring sufficient iodine levels and optimal TH function during pregnancy is crucial for the cognitive development of children. This highlights the im-portance of nutrition and regular monitoring of thyroid health in pregnant women. This re-view focuses on the key mechanisms of thyroid hormone homeostasis and discusses the implications of iodine deficiency during pregnancy.

Background: Thyroglobulin (Tg) is a biomarker of iodine status. Newborn Tg is a more sensitive marker than neonatal TSH in detecting variations in iodine intake. This study aims to validate an enzyme-linked immunosorbent assay (ELISA) for Tg determination on dried blood spots (DBS) in newborns. This study also sets out to assess the stability of Tg and the influence of newborns’ hematocrit on Tg determination. Methods: A commercially available ELISA Tg assay was adapted for use on DBS. DBS-Tg in cord blood was measured in 209 newborns delivered from healthy euthyroid pregnant women. Sensitivity, linearity, repeatability, and intermediate fidelity were determined using the appropriate standards and quality control materials. Results: The limit of detection of the DBS-Tg assay was 2.4 µg/L, and the limit of quantification was 5.8 µg/L. Repeatability and intermediate fidelity were 7.7–8.3% and 11.0–11.2%, respectively. The median cord plasma Tg and DBS-Tg values in newborns were not significantly different, 30.2 (21.3–44.4) µg/L and 31.6 (19.3–48.7) µg/L (P = 0.48) with the ELISA, respectively, and 76.5 (40.0–101.5) µg/L with the Elecsys assay with an R = 0.88. DBS-Tg concentrations decrease with increasing hematocrit values (P < 0.05). DBS-Tg values were stable at a concentration of 25 µg/L for 12 months at −20ºC and 4ºC. Conclusion: This DBS-Tg assay demonstrated good analytical performance over a wide range of Tg concentrations, suggesting it is well suited to detecting variations in Tg concentrations. Studies comparing populations with different prevalence of anemia should consider the effect of hematocrit on DBS-Tg determination. The availability of a DBS-Tg assay for newborns makes it possible to integrate iodine status monitoring with newborn screening for inherited metabolic diseases.