Levothyroxine dosage and related factors in the treatment of pregnant women with subclinical hypothyroidism

Objective To study the levothyroxine doses and related factors in the treatment of pregnant women with subclinical hypothyroidism (SCH).Methods Fifty-six pregnant women with SCH (diagnosed before 12 weeks of gestation) were recruited and divided into 2 groups according to the baseline TSH levels,SCH group 1 (2.5 mIU/L ≤ TSH ≤ 5.0 mIU/L,n =24) and SCH group 2 (TSH＞5.0 mIU/L,n =32).Thyroid autoantibodies [thyroid peroxidase antibody(TPOAb) and thyroglobulin antibody(TGAb)] were detected.All the subjects were treated with levothyroxine and the doses were adjusted according to the TSH level.The therapeutic target was to keep the TSH levels under control,0.3 to 2.5 mIU/L for the first trimester and 0.3 to 3.0 mIU/L for the second and third trimesters.Results There was a positive correlation between the levothyroxine doses and baseline TSH levels (r =0.533,P＜0.01) in pregnant women with SCH.A significant difference in the levothyroxine doses between SCH group 1 and SCH group 2 was found [(0.583 ± 0.341) vs (0.961 ± 0.405) μg/kg,t =-3.695,P＜ 0.01].The levothyroxine doses in SCH group 2 were 64.84％ higher than those in group 1.There was a significant difference in the levothyroxine doses between thyroid autoantibody negative and positive subjects [(0.680 ± 0.370) vs (0.918 ±0.440) μg/kg,t =-2.197,P =0.032].The levothyroxine doses in thyroid autoantibody positive subjects were 35 ％ higher than those in the negative subjects.In addition,there was a significant difference in the levothyroxine doses between subjects with negative and positive thyroid autoantibody [(0.421 ± 0.192) vs (0.720 ± 0.385)μg/kg,t =-2.331,P =0.029] in SCH group 1.While in SCH group 2,the difference did not reach statistical significance.Conclusion The baseline TSH levels and status of thyroid autoantibodies may affect the levothyroxine dosage in pregnant women with SCH. Key words: Pregnancy; Hypothyroidism; Levothyroxine; Thyroid autoantibodies