Objective To investigate the effects of selenium yeast tablets combined with levothyroxine on free triiodothyronine（FT

3

）

thyroid stimulating hormone（TSH） and free tetraiodothyronine（FT

4

） levels in patients with hypothyroidism during pregnancy. Methods One hundred and sixteen patients with hypothyroidism during pregnancy admitted to a hospital in Henan Province from October 2019 to October 2020 were selected for the study

and the patients were divided into a control group（n=58） and a study group（n=58） using a random number table. Patients in the control group were treated with levothyroxine

while patients in the study group were treated with selenium yeast tablets combined with levothyroxine

and both groups received continuous treatment until the end of pregnancy. The clinical efficacy of patients in the two groups was compared; the adverse pregnancy outcomes and the occurrence of adverse reactions in the two groups were compared; the serum FT

3

TSH and FT

4

levels of patients in the two groups before and after treatment were compared. Results The total number of effective cases in the control group was 44

and the total effective rate was 75.9%; the total number of effective cases in the study group was 55

and the total effective rate was 94.8%. The total effective rate of treatment in the study group was significantly higher than that in the control group（P

<

0.05）. The number of patients in the control group with adverse pregnancy outcome was 11

and the incidence of adverse pregnancy outcome was 19.0%; the number of patients in the study group with adverse pregnancy outcome was 2

and the incidence of adverse pregnancy outcome was 3.4%. The incidence of adverse pregnancy outcomes in the study group was significantly lower than that in the control group（P

<

0.05）. The number of adverse reactions in the control group was 11（3 cases of pruritus and 8 cases of vomiting）

and the incidence of adverse reactions was 19.0%. The number of adverse reactions in the study group was 3（1 case of skin itching and 2 cases of vomiting）

and the incidence of adverse reactions was 5.1%. The incidence of adverse reactions in patients in the study group was significantly lower than that in the control group（P

<

0.05）. Before treatment

there was no statistically significant difference between the serum FT

3

FT

4

and TSH levels of patients in the 2 groups（P

>

0.05）. After treatment

the serum FT

3

and FT

4

levels of patients in the 2 groups were higher than those before treatment

and those of the patients in the study group were significantly higher than those in the control group（P

<

0.05）; the serum TSH levels of patients in the 2 groups were significantly lower than those before treatment

and those of patients in the study group were significantly lower than those in the control group（P

<

0.05）. Conclusion Selenium yeast tablets combined with levothyroxine can effectively improve serum FT

3

FT

4

and TSH levels in patients with hypothyroidism during pregnancy and reduce the incidence of adverse reactions and adverse pregnancy outcomes in patients after medication. The efficacy of the therapy is significant

and it can be promoted.