Evaluation of urinary iodine concentration, thyroid volume, and thyroid function in the first trimester of pregnancy

Iodine is a crucial element for thyroid hormone synthesis and plays an important role in regulating the body's basal metabolism. The aim of our study was to evaluate iodine status, thyroid volume, and thyroid function in pregnant women during the firsttrimester of pregnancy.

This study included 130 healthy pregnant women in their first trimester between November 2022 and May 2024. However, urinary iodine concentration (UIC) data could not be obtained for two participants, and urinary iodine/creatinine ratio datawere missing for four participants because of insufficient sample volume. Laboratory tests, including free triiodothyronine (fT3), freethyroxine (fT4), thyroid-stimulating hormone (TSH), and thyroglobulin (Tg), were performed. First-morning single-spot urine samples were collected, and urinary iodine and creatinine concentrations were determined. The urine iodine/creatinine ratio (μg/g) was calculatedusing the following equation: urine iodine (μg/L)/urine creatinine (mg/dL) × 100. The thyroid gland, including thyroid volume, wasevaluated using ultrasonography.

The median UIC was 107.00 μg/L, indicating mild iodine insufficiency at the population level according to the World Health Organization criteria for pregnancy. Analysis of the spot urine samples revealed that 90 samples had a UIC below 150 μg/L. When the relationshipbetween the urine iodine/creatinine ratio and the measured parameters was investigated, Tg levels (p = 0.006) and thyroidvolume (p = 0.039) were significantly higher in the group with a urine iodine/creatinine ratio below 50 μg I/g Cr.

The statistically significant associations between the urine iodine/creatinine ratio and both Tg and total thyroid volume suggest a potential relationship between these parameters and lower urinary iodine/creatinine ratios.