Study on subclinical abnormalities of thyroid function in pregnant women in iodine sufficient areas

Objective To study subclinical abnormalities of thyroid function during different trimesters of pregnancy in iodine sufficient areas and provide evidence for monitoring iodine nutrition or screening for thyroid function. Methods The urinary iodine levels and thyroid function were investigated for 160 pregnancy and 51 non-pregnancy subjects of 5 hospitals in Hangzhou. The urinary iodine concentration was measured by arsenic-cerium contact processing method. The serum TSH,FT4,TT4,FT3,TT3 and TPOAb were measured by chemiluminescence method. Results The median concentration of urinary iodine in the 1st,2nd and the 3rd trimester of pregnancy was not different from that of non-pregnant women (Z=2.21,P=0.53). The rate of subclinical abnormalities of thyroid function was 10.0%(16/160)based on trimester-specific reference intervals of thyroid hormones for normal pregnancy.The rate of missed diagnosis of subclinical hypothyroidism would be 8.75%(14/160)according to the population-based reference intervals. There was significant difference in detecting subclinical hypothyroidism with the two reference intervals(χ2=8.46,P=0.04). Conclusion We should evaluate thyroid function in pregnant women with trimester-specific reference intervals of thyroid hormones for normal pregnancy.More than half of the pregnant women in Hangzhou had good nutritional status of iodine,while 10.0% of them had maternal subclinical thyroid abnormalities.The thyroid function screening is recommended for pregnant women,especially in the 1st and 2nd trimester.