Objective To investigate the influence of hypothyroidism on pregnancy outcome and fetus in pregnant women.Methods A total of 4 286 pregnant women,who received prenatal examination in our hospital from January 2013 to October 2015,were selected as study subjects.The incidence of hypothyroidism and the influence on pregnancy outcomes and fetus were investigated.Results In 4 286 pregnant women surveyed,209 hypothyroidism cases were detected (4.9％),including 85 clinical hypothyroidism cases and 124 subclinical hypothyroidism cases.In health group,the premature delivery rate was 1.0％,significantly lower than that in clinical hypothyroidism group (10.6％) and in subclinical hypothyroidism group (6.5％),the differences were significant (χ2=38.884,P＜0.001;χ2=17.722,P＜0.001).In healthy group,the incidence of anemia was 3.8％,significantly lower than that in clinical hypothyroidism group (18.8％) and in subclinical hypothyroidism group (9.7％),the differences were significant (χ2=30.949,P＜0.001;χ2=23.275,P＜0.001).In health group,the incidence of low birth weight was 1.1％,significantly lower than that in clinical hypothyroidism group (14.1％) and in subclinical hypothyroidism group (4.8％),the differences were significant (χ2=50.593,P＜0.001;χ2=15.637,P＜0.001).In health group,the fetal distress incidence was 1.9％,significantly lower than that in clinical hypothyroidism group (10.6％) and in subclinical hypothyroidism group (5.6％),the differences were significant (χ 2=19.257,P＜0.001;χ2=12.357,P＜0.001).In health group,the fetal Apgar score (9.69 ± 0.32) was significantly higher than those in clinical hypothyroidism group (9.25 ± 0.45) and in subclinical hypothyroidism group (9.28 ± 0.44),the differences were significant (t=8.823,P＜0.001;t=15.175,P＜0.001).Conclusion Hypothyroidism during pregnancy has adverse influences on pregnancy outcome and fetus,and it is necessary to strengthen the hypothyroidism detection in pregnant women for the early treatment.