Iodine Sufficiency during Pregnancy in Latvia. Summary of the Doctoral Thesis
Authors:   ,   Rīga Stradiņš University, Veisa Vija 
Published: November 2024

Globally, iodine deficiency after starvation is the next most common cause of potentially preventable brain damage. The iodine is essential micronutrient for production of thyroid hormones. Even mild iodine insufficiency during pregnancy can lead to maternal hypothyroxinemia and decreased transplacental transfer of thyroid hormones with further negative effect on the proliferation and migration of foetal neurons and decreased neuroplasticity of foetal brain. Thus, sufficient intake of iodine during pregnancy is particularly important not only in individual terms, but also affects the national social and economic development – lower intelligence quotient (IQ) is related to decreased learning capacity and lower educational levels, hence lower income and welfare. Universal salt iodisation is the main strategy recommended by the World Health organization (WHO) to prevent iodine deficiency. It has been successfully implemented in many countries worldwide over the past 25 years. In Latvia, similarly to other European regions, population studies indicate persisting mild (at least seasonal) iodine deficiency, nevertheless, the use of iodised salt in households and food industry is still voluntary. Particularly vulnerable part of the population in mild to moderate iodine deficiency regions are pregnant women – demand of iodine significantly increases already in first weeks of pregnancy. To replace presumptions with scientific evidence, the aim of the study was to evaluate iodine sufficiency among pregnant women in Latvia. After revealing iodine deficiency in all trimesters of pregnancy, further aim was to assess whether information activities, carried out among healthcare professionals and women of reproductive age, is associated with improved iodine intake. For evaluation of iodine sufficiency during pregnancy, in 2013 urinary iodine was measured to pregnant women in various regions of Latvia. Information regarding consumption of iodine containing supplements and dietary products was obtained from questionnaires, completed by women. Results – urinary iodine was measured in 696 women from various regions of Latvia in 2013. The median creatinine (Cr) standardised urinary iodine concentration (UIC) was 80.8 (interquartile range (IQR) 46.1–130.6) μg/g Cr and approved iodine deficiency during pregnancy (150–250 μg/g indicates optimal iodine intake during pregnancy according to WHO recommendations). Median UIC was significantly lower in the first trimester, during the most important period of foetal brain development and organogenesis, compared to the second and third trimesters (p < 0.001 in both trimesters). After 5 years, which is the WHO recommended time for re-monitoring iodine intake in population, median urinary iodine in pregnant women (n 129) during the first trimester revealed that iodine intake has improved (143.1 (IQR 89.9–228.9) μg/g Cr), however remained below optimal. While analysis of dietary habits did not reveal any significant change in consumption of iodine-containing food products in recent years, for half of pregnant women in the first trimester the iodine intake is sufficient. One explanation that can be attributed to improved iodine intake, is higher number of women taking supplements during the first trimester of pregnancy, including those with iodine concentrations ≥ 150 μg (50.3 %, among them with iodine ≥ 150 μg 3.1 % in 2013, and 68.2 %, among them with iodine ≥ 150 μg 14.7 % in 2018). Newborn’s TSH screening data in 2019 reveals that 5.6 % (95 % CI 5.2–5.9 %) of newborns were detected TSH > 5 mIU/L, and in 2022 – 8.8 % (95 % CI 8.4–9.3 %) with TSH > 5 mIU/L. According to the criteria recommended by WHO (newborn ratio 3.0–19.9 % with TSH above 5 mIU/L indicates mild iodine deficiency in the population), newborn TSH screening confirms mild iodine deficiency in Latvia. Thus, all women in childbearing age should be advised to increase consumption of iodine containing dietary products, including iodised salt, but more global solutions are hampered by the fact that iodine intake has a U-shaped effect – both, very high and low concentrations can be harmful. The higher iodation of thyroglobulin is associated with higher autoantigenicity and therefore the detection of serum selenium levels in pregnant women, which may reduce autoimmune reactions as a cofactor of selenoenzymes, was an important aspect in research. The detected mean serum selenium level 102.07 ± 37.01 μg/L is not optimal, according to opinion of many researchers, but is sufficient to ensure the activity of antioxidative enzymes, thus reducing the risk of postpartum thyroiditis or thyrotoxycosis – side effects related to iodine intake. Results of the research, carried out for the first time in Latvia, suggest that information activities should be regular, they are safe, effective, but re-monitoring of median urinary iodine in population is necessary to ensure optimal iodine intake, which is still insufficient during pregnancy. The Doctoral Thesis was developed at Rīga Stradiņš University, Department of Obstetrics and Gynaecology, Latvian Institute of Organic Synthesis. Defence: at the public session of the Promotion Council of Clinical Medicine on 5 November 2024 at 15.00 in the Hippocrates Lecture Theatre, 16 Dzirciema Street, Rīgas Stradiņš University and remotely via online platform Zoom. 3.2 Clinical Medicine; Sub-Sector – Obstetrics and Gynaecology. Keywords: ioduria; iodine intake; pregnancy.