Assessment of Iodine Status in Pregnant Women: Diagnostic Performance of Spot Urinary Iodine Indices Compared with 24-h Urinary Iodine Excretion

Background: Adequate iodine intake during pregnancy is essential for optimal maternal thyroid function and fetal neurodevelopment. Although universal salt iodization has been implemented in Turkey, pregnant women may remain vulnerable to iodine insufficiency. This study aimed to evaluate maternal thyroid function in relation to iodine status, and to comprehensively compare the diagnostic performance of spot urinary indices and creatinine-adjusted measures against measured 24 h urinary iodine excretion (24h-UIE) in pregnant women. Methods: A total of 227 pregnant women attending family health centers in Afyonkarahisar, Turkey, provided both spot urine samples and complete 24 h urine collections. Urinary iodine concentration (UIC), creatinine-corrected UIC (UIC/UCr), and 24h-UIE were measured. Thyroid function tests were interpreted using trimester-specific reference ranges. Correlations between urinary indices were assessed, and ROC analyses were performed using 24h-UIE as the operational reference. A structured questionnaire evaluated iodine-related dietary knowledge and salt-use practices. Results: The median spot UIC was 59.0 µg/L, indicating insufficient recent iodine intake at the population level. Based on 24h-UIE, 70% of participants had excretion levels below the Estimated Average Requirement (EAR) threshold (