Dynamic changes of thyrotropin and thyroid hormones during the pregnancy in iodine-adequate area

Objective To explore the dynamic changes of serum TSH and thyroid hormones of the pregnant women with normal thyroid during the pregnancy and to observe the occurrence of subclinical hypothyroidism in these women during the pregnancy.Methods 239 pregnant women with normal thyroid were followed up regularly from G12 to G36 with the interval of 4 weeks.All the subjects underwent the planned thyroid tests regularly.Serum TSH,TT4,FT4,TT3,FT3,TPOAb and TgAb were measured.The incidence of subclinical hypothyroidism was obtained using trimester-specific reference intervals of TSH and thyroid hormones.Results Serum TSH decreased to nadir at G12 (compared with other points,P0.01) and then increased gradually.Serum TT4 increased to the peak at G12 (G12 vs.G6,P0.01) and remained at the high level thereafter.Serum FT4 decreased gradually from the first trimester (G12 vs.G6,P=0.019) till the end of the pregnancy.Serum TT3 and FT3 increased gradually before G16,and stayed at the high level thereafter.6.7% of pregnant women with normal thyroid at G6 presented subclinical hypothyroidism during the pregnancy.The baseline TSH levels of the pregnant women who had subclincal hypothyroidism later were higher than those of others (P0.01).The incidence of subclinical hypothyroidism in the pregnant women with baseline TSH2.5 mIU/L was 17.5% (14/80),which was higher than that in the pregnant women with baseline TSH≤2.5 mIU/L (P0.01).Conclusion The levels of serum TSH and thyroid hormones fluctuate at the different phases of pregnancy.The pregnant women with baseline TSH2.5 mIU/L are susceptible to subclinical hypothyroidism.