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

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.