Objective: To explore the effect of hypothyroidism during pregnancy on maternal and infant pregnancy outcomes. Methods: A total of 771 cases of hypothyroid pregnant women who were examined in the obstetric outpatient department and hospitalized for delivery in Wuxi Maternity and Child Health Hospital from January 2016 to June 2019 were selected as subjects. Among them, 81 cases of clinical hypothyroidism were regarded as hypothyroidism group, and 690 cases of clinical hypothyroidism cases were regarded as hypomethylene group, and randomly sampling 420 cases of normal pregnant women as control group. Then comparative analysis on thyroid function (TSH and FT4 levels), pregnancy complications and outcomes (gestational diabetes, gestational hypertension, premature rupture of membranes, abnormal amniotic fluid, postpartum hemorrhage), adverse perinatal outcomes (fetal distress, miscarriage or stillbirth, premature birth, neonatal asphyxia, etc.) were adopted. Results: The incidence rate of hypothyroidism in the 30 698 cases of pregnant women was 2.51% (771/30 698). There was no significant difference in age, BMI before pregnancy, parity and gestational week among the three groups (P<0.05). TSH levels in the second and third trimesters of hypothyroidism and hypomethylene were higher than those of the control group (P<0.05), and FT4 levels were lower than those of the control group (P<0.05); the level of TSH in the second and third trimesters of the hypothyroidism group was higher than that of the hypothylene group (P<0.05), and the level of FT4 was lower than that of the hypothylene group (P<0.05). The incidences of gestational diabetes, gestational hypertension, premature rupture of membranes, and abnormal amniotic fluid in the hypothyroid group were higher than those in the control group (P<0.05). In the hypothylene group, the incidence of gestational diabetes, gestational hypertension, and premature rupture of membranes was higher than that of the control group (P<0.05), while the incidence of gestational diabetes and premature rupture of membranes in the hypothylene group was higher than that of the hypothyroid group (P<0.05). The incidences of fetal distress, premature delivery and neonatal asphyxia in the hypothyroid group and hypothylene group were higher than those in the control group (P<0.05), while the incidence of neonatal asphyxia in the hypothyroidism group was higher than that in the control group (P<0.05). Conclusion: Pregnant women have a relatively high incidence rate of hypothyroidism during pregnancy. We should early screen and treat hypothyroidism during pregnancy, adjust thyroid hormone level in pregnant women, to improve pregnancy outcomes of maternal and infant.