Occurrence of clinically relevant thyroid nodules in adults

Background: We aimed to comprehensively investigate the occurrence of thyroid nodules in a nationally representative population as well as in women of reproductive age from a geographic area with adequate iodine intake over the last two decades. Patients and methods: This prospective cross-sectional study included 653 adult participants from three groups: a nationally representative gender-mixed group (205 participants) and women of reproductive age, including non-pregnant (306 participants) and pregnant (142 participants) women. For each participant, demographic data were collected, thyroid-stimulating hormone (TSH) levels were measured, thyroid volume was estimated, and the presence and size of thyroid nodules were recorded with high-resolution ultrasound. The ultrasound characteristics were analysed. Results: Among the nationally representative participants, nodules were detected in 44.9%, with 39.0% larger than 5 mm and 13.7% larger than 0.5 mL. Among women of reproductive age, nodules were detected in 22.5%, with 14.1% larger than 5 mm and only 2.0% greater than 0.5 mL. The prevalence and size of nodules increased significantly with age in all groups, being significantly lower in non-pregnant women than in pregnant women, who were also older. In non-pregnant women of reproductive age, the number of nodules increased significantly after the age of 25, with the number of nodules larger than 5 mm increasing only after the age of 40. Conclusions: Thyroid nodules are prevalent in the population, but are rarely clinically significant. Therefore, screening for thyroid nodules in asymptomatic individuals with normal thyroid findings on clinical examination should be avoided.