ABSTRACT
Objective To investigate the characteristics of maternal thyroid function of pregnant women with negative thyroid antibody in high water iodine area. Methods The investigation sites were selected,which were the Hospital for Women and Children of Jinghai county in the high water iodine area(drinking iodine > 200 μg/L) and the Hospital for Women and Children of Heping district in Tianjin in the adaptive iodine area (drinking iodine < 10μg/L,popularization rate of iodized salt > 90％,residents urinary iodine > 200μg/L). In the maternal and child hospitals,50 pregnant women of each stage from obstetric clinics in first,second,third term of pregnancy were selected,the blood samples were collected and the thyroid function were measured with chemiluminescence. Water,salt and diurnal optional urine samples were measured for iodine concentration. Iodine levels of urine,water,salt were determined respectively by As-Ce catalysis spoctrophotometry method,quantitative determining kit which use time-recorded determination by catalytic effect on the As-Ce reaction and sodium hyposulfite titration method. Results ①In pregnant women with negative thyroid antibody,serum TT_4,TT_3,FT_4 in first term of pregnaney and TT_4,TT_3 in second term of pregnancy were significantly lower in high water iodine area than low water iodine area(111.97 nmol/L vs 140.46 nmoL/L,Z = 3.56,P < 0.01 ; 1.86 nmol/L vs 2.26 nmol/L,Z = 2.35, P < 0.05; 14.13 pmol/L vs 16.32 pmol/L,Z = 5.14,P < 0.01,and 11.98 pmol/L vs 14.30 pmol/L,Z = 5.75,P < 0.01 ; 4.04 pmol/L vs 4.32 pmol/L,Z = 2.76,P < 0.01),while TT_3 and TSH in third term of pregnancy were significantly higher(2.88 nmoL/L vs 2.70 nmol/L,Z=-2.27,P< 0.05; 2.37 mU/L vs 1.75 mU/L,Z =-2.70, P < 0.01).②Concentration of water iodine and urine iodine were higher(205.57μg/L vs 8.26 μg/L,Z =-14.71,P < 0.01 ; 305.91 g/L vs 191.86 g/L,Z =-5.30,P < 0.01),while salt iodine was lower(26.5 mg/kg vs 31.7 mg/kg,Z =-5.86,P < 0.01) in high water iodine area. ③Among 290 selected healthy pregnant women without medical history of thyroid diseases,there was no significant difference in positive rate of thyroid antibody in each term of pregnancy between high water iodine area and low water iodine area(10.20％ vs 10.64％ ; 14％ vs 9.52％ ; 4％ vs 7.69％ ; all P > 0.05). Conclusions The thyroid function of pregnant women with negative thyroid antibody in high water iodine area is different from pregnant women in low water iodine area with universal salt iodization. Enhanced monitoring on thyroid function of pregnant women in high water iodine area should be performed,especially in first and second trimester.