Analysis of urinary iodine and thyroid function in pregnant women of Hangzhou

Objective To investigate the urinary iodine level and thyroid function during different trimesters of pregnancy in Hangzhou residents and to provide evidence for monitoring iodine nutrition or screening thyroid function. Methods The urinary iodine level and thyroid function of 395 subjects from 5 hospitals in Hanzhou were investigated. The urinary iodine level was measured by arsenic-cerium contact process method. The serum TSH, FT3 and FT4 were measured by chemiluminescence method. Results (1) The urinary iodine median concentration during pregnancy in the 1st, 2nd and 3rd trimesters were 170.3, 170.2, 162.4 μ/L respectively, all significantly lower than that of non-pregnant women (251.9 μg/L, all P < 0.05); (2) The mean value of TSH during the 1st trimester of pregnancy was significantly lower than that of non-preguant women (P < 0.05). The mean values of FT4 and FT3 in the 2nd and the 3rd trimesters of pregnancy were significantly lower than those of the control (P < 0.05); (3) During 2nd trimester, there were 8.7% (9/104, in FT4) and 9.6% (10/104, in FT3) pregnant women below normal lower range while during 3rd trimester, these figures reached 22.7% (22/97) and 17.5% (17/97) resfectively. Conclusions More than half of the pregnant women in Hangzhou have good nutritional status of iodine. There are significant differences in thyroid hormone levels between the non-pregnant and pregnant women as well as between gestation periods. Therefore, it is necessary to establish a trimester-specific reference range of thyroid hormones for normal pregnancy. The screening for thyroid function is recommended for pregnant women besides monitoring routine urinary iodine. Key words: Pregnancy; Urinary iodine; Thyroid function