To explore the therapeutic effect at different stages of pregnant women with hypothyroidism, and to study their serum thyroid stimulating hormone (TSH), FT4, Thyroid peroxidase antibody (TPOAb) levels, and their pregnancy outcomes. Methods: 120 pregnant women with hypothyroidism were selected and were divided into group A (60 women with L-T4 treatment before 8 gestational weeks) and group B (60 women with L-T4 treatment after 8 gestational weeks) from 30 June 2017 to 30 May 2018. Another 60 healthy pregnant women were randomly selected in group C during the same time. The levels of TSH, FT4, TT4 and TPOAb of women in the three groups during different stages of pregnancy were detected. Results: Before treatment, the serum TSH, FT4, TT4 and TPOAb levels of women in group A and group B were significant different from those of women in group C (P＜0.05). After treatment, the serum TSH, FT4, TT4 and TPOAb levels of women in group A and group B during 30 gestational weeks had no significant different from those of women in group C (P＞0.05). The proportions of spontaneous abortion, gestational diabetes mellitus, and placental abruption of women in group A were significant lower than those of women in group B (P＜0.05), but those of women in group A had no significant different from those of women in group C (P＞0.05). There were no significant differences in the rates of gestational hypertension and low birth weight of women between group A and B and group C (P＞0.05). Gesell scale scores of the babies of the women in group A at 6 months and 12 months old were significant higher than those of babies of women in group B (P＜0.05), but which had no significant difference between group A and group C (P＞0.05). Conclusion: Intervention for pregnant women with hypothyroidism early can reduce the incidence of adverse perinatal outcomes effectively and can ensure the early development of newborns.