Abstract: Objective: To investigate the levothyroxine(L-T4) dose in the treatment of patients with subclinical hypothyroidism(SCH) during pregnancy.Methods: The thyroid functions of 42 patients with SCH during pregnancy were detected every 4 weeks,the L-T4 dose was adjusted according to the level of thyroid stimulating hormone(TSH) to make the TSH arrive at the standard scope.The patients weight,TSH value and the level of thyroid peroxidase antibodies(TPO-Ab) at initial diagnosis,and neonatal weight and prenatal patients weight were recorded.The prenatal L-T4 dose was analyzed by multiple linear regression with SPSS17.0.Results: There were not significant relationships between the prenatal L-T4 dose and patients weight,pregnant woman increasing weight,TSH value and the level of TPO-Ab at initial diagnosis,and neonatal weight(P>0.05).Conclusions: The patient weight and TSH value,pregnant woman increasing weight,the level of TPO-Ab at initial diagnosis,and neonatal weight can not predict the prenatal L-T4 dose.Controlling the TSH value depends on the regular monitoring and following-up.