Pregnant women with low free thyroxine, the result of 11 pmol/L, consider the existence of physiological causes and pathological causes, generally physiological need no treatment, pathological need treatment. Due to the different examination methods and reagents, the reference indexes of each hospital are different and need to be analyzed specifically. 1. Physiological causes: the free thyroxine level is higher than normal in the early stage of pregnancy due to the influence of human chorionic gonadotropin level in the body, while the free thyroxine level gradually decreases in the middle and late stages of pregnancy. 2. Pathological causes: When pathological causes of low free thyroxine are suspected, the first step is to assess the thyrotropin level of the pregnant woman, and when the free thyroxine level is low and the thyrotropin level is high, it is considered that hypothyroidism exists, and supplementation of levothyroxine may be needed under the guidance of the doctor to carry out replacement therapy. If there is any change in the free thyroxine level of pregnant women, they can consult doctors in regular hospitals for diagnosis and treatment, and should not be negligent to avoid delaying the condition.