Thyroid function and autoimmunity in pregnancy: contributing factors and a real-life performance of reference ranges recommended by the national guidelines: results of the longitudinal study
Year: 2026
Type: article
Study design: Observational Study
Abstract: INTRODUCTION: Thyroid dysfunction and thyroid autoimmunity during pregnancy are linked to an increased risks of adverse maternal and fetal outcomes. Guidelines recommend population‑specific thyroid hormone reference ranges in pregnancy, though adherence and effectiveness vary. OBJECTIVES: We aimed to evaluate the performance of thyroid function reference ranges recommended by Polish national guidelines in pregnancy and to assess clinical and demographic factors affecting thyroid hormone levels and autoimmunity. PATIENTS AND METHODS: A cohort of 1339 pregnant women across all trimesters was recruited in Poland (2007-2017). Serum levels of thyroid‑stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), and thyroid peroxidase antibodies (TPOAbs), and urinary iodine concentration (UIC) were measured. Associations between thyroid status and maternal age, body mass index (BMI), gestational age, and UIC were analyzed. RESULTS: Over 91% of the participants had TSH concentrations within Polish trimester‑specific reference ranges. TPOAbs were positive in 12% of the cases, and were strongly associated with higher TSH and lower FT4 concentrations (P <0.001). TSH level was negatively associated with FT4 concentrations and age (P <0.001), and positively with TPOAb (P <0.001). FT4 concentrations were positively associated with TPOAb (P = 0.04) and FT3 concentrations (P <0.001), but negatively influenced by trimester, TSH, age, BMI, and pregnancy week (P <0.001). CONCLUSIONS: TPOAb presence correlated with elevated TSH concentrations and impaired FT4 response, which supported the role of TPOAb as a key marker in pregnancy screening. Maternal age and BMI significantly influenced FT4 levels, pointing at the new factors to be considered when interpreting thyroid function tests results. Our findings support current Polish reference ranges and emphasize the need for locally adapted criteria in thyroid management during pregnancy.
DOI: 10.20452/pamw.17186
Language: English
Subfield: Endocrinology, Diabetes and Metabolism
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W7118259762