Pregnancy is accompanied by profound alterations in thyroid economy and relative iodine deficiency. The aim of this study was to evaluate urinary iodine excretion of pregnant women in cities with adequate and more than adequate iodine intake.

A cross-sectional study was performed on schoolchildren and pregnant women in four cities in the Islamic Republic of Iran. Urinary iodine excretion was measured for 438 schoolchildren and 403 pregnant women. In addition, in Isfahan City, thyroid volume was measured by sonography for 30 pregnant women in each trimester of pregnancy and for 90 non-pregnant women who also had urinary iodine measurement.

Median urinary iodine of schoolchildren was 31.2, 25.0, 20.2 and 19.3 μg/dl in Rasht, Isfahan, Ilam and Tehran, respectively. Corresponding values for pregnant women were 33.8, 21.2, 19.0 and 18.6μg/dl. The percentage of pregnant women with urinary iodine below 20μg/dl was 16, 45, 55 and 54, and below 10μg/dl was 1, 7, 7 and 13, in Rasht, Isfahan, Ilam and Tehran, respectively. In Isfahan, urinary iodine was significantly decreased in the third trimester of pregnancy, compared with controls. Mean thyroid volume was 7.8±3.1 ml and 7.8±2.8 ml in pregnant and non-pregnant women, respectively.

Recommended values for dietary iodine through universal salt iodisation may not be adequate for pregnant women, and the specific problem of iodine and pregnancy should be considered further in the light of the latest recommendations.