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Objective To validate urinary iodine (I) excretion and the simplified classification of goiter by palpation, comparing them with ultrasound of the thyroid gland as the gold standard, to identify endemic goiter in pregnant women.

Population and setting 300 pregnant women identified in referral hospitals, in three geographic regions.

Methods Two endocrinologists, previously trained, evaluated thyroid size by palpation and by ultrasound. Urinary iodine excretion in a sample of urine was determined. Thyroid size below the 90th centile by ultrasound was considered normal.

Results Mean age of study women was 23 years old. The prevalence of low weight for gestational age was 39% and of anaemia 47%. Our sample distribution showed that 120 μg I/L was the best cut off for low urinary iodine excretion to identify endemic goiter in pregnant women (sensitivity 57% and specificity 70%, likelihood ratio of 1.4). The prevalence of goiter was 10% using ultrasound. Palpation had a sensitivity of identification goiter of 94% (95% CI 89–99%), a specificity of 80% (95% CI 75–85%), a likelihood ratio of 4.7, positive post-test probability of 36.5% and negative post-test probability of 99%.

Conclusions Low urinary iodine excretion identified up to 46% of women with goiter. This test by itself is not useful as a screening tool to identify pregnant women at risk of goiter. Identification of thyroid size by palpation was a better screening test. However, when both tests were combined in parallel, up to 100% of women with goiter were correctly identified. Our results suggest that the commonly used cut off point of 100 μg I/L to identify low urinary iodine excretion may under-estimate the prevalence of iodine deficiency disorders when used during pregnancy.