Objective To investigate the influencing factors and pregnancy outcomes of isolated hypothyroinemia (IH) in early pregnancy.Methods A total of 117 pregnant women with IH (IH group) who gave birth in the Third Affiliated Hospital of Zhengzhou University from September 2021 to February 2024 were retrospectively analyzed, and 117 pregnant women with normal thyroid function were selected as the control group. Binary logistic regression analysis was used to explore the influencing factors of IH. Spearman rank correlation analysis was used to investigate the correlation between FT4 level and related indicators. The pregnancy outcomes between the two groups were compareed.Results The levels of serum ferritin, hemoglobin (Hb), iron and high density lipoprotein (HDL) in IH group were lower than those in control group, and age, serum triglyceride (TG) level, the incidence of iron deficiency and anemia in IH group were higher than those in control group (P<0.05). Binary logistic regression analysis showed that age (O^R=1.109, 95%CI: 1.034–1.190, P=0.004), iron deficiency (O^R=6.720, 95%CI: 2.488–18.153, P<0.001), anemia (O^R=9.806, 95%CI: 2.863–33.586, P<0.001), TG increased (O^R=2.116, 95%CI: 1.498–2.988, P<0.001) were risk factors for IH, and ferritin increased (O^R=0.975, 95%CI: 0.965–0.985, P<0.001), Hb increased (O^R=0.889, 95%CI: 0.858–0.922, P<0.001), HDL increased (O^R=0.392, 95%CI: 0.186–0.828, P=0.014) were protective factors for IH. FT4 was negatively correlated with TG (r_s=-0.375, P<0.001), birth weight (r_s=-0.233, P<0.001), length (r_s=-0.157, P=0.019), and positively correlated with ferritin (r_s=0.373, P<0.001), Hb (r_s=0.459, P<0.001), HDL (r_s=0.164, P=0.012). The incidence of gestational diabetes mellitus (GDM) and macrosomia, neonatal birth weight and length in IH group were higher than in the control group (P<0.05), and after controlling for confounding factors, IH was only associated with GDM (O^R=2.112, 95%CI: 1.006–4.434, P=0.048).Conclusion Age, ferritin, Hb, iron deficiency, anemia, TG and HDL are the influencing factors of IH in early pregnancy. IH in early pregnancy increases the risk of GDM and affects the growth and development of newborns.