Objective To explore the diagnostic value of serum hemoglobin (HGB), ferritin (SF) and transferrin receptor (TfR) in patients with mild thalassemia in the second and third trimesters of pregnancy. Methods During the period from August 2017 to July 2019, 40 patients with mild thalassemia in the second trimester of pregnancy and 40 patients in the third trimester of pregnancy who received treatment in our hospital were enrolled, another 40 healthy people during the same period were enrolled as healthy control group. The levels of serum HGB, SF and TfR were compared among the three groups. The correlation among the three indexes and their correlation with thalassemia were analyzed. And the diagnostic value of serum HGB, SF and TfR levels for thalassemia was analyzed. Results The levels of HGB and SF in second trimester group and third trimester group were lower than those in healthy control group, while TfR level was higher than that in healthy control group (P<0.05). The levels of HGB and SF in third trimester group were lower than those in second trimester group, while TfR level was higher than that in second trimester group (P<0.05). The level of serum TfR was negatively correlated with levels of serum HGB and SF, while level of serum HGB was positively correlated with SF level (P<0.05). The levels of serum HGB and SF were negatively correlated with the occurrence of thalassemia, while level of serum TfR was positively correlated with it (P<0.05). ROC curve analysis showed that AUC of serum HGB combined with SF and and TfR for diagnosis of thalassemia was greater than that of single index (P<0.05). Conclusion The combined detection of serum HGB, SF and TfR levels is of diagnostic value for mild thalassemia in the second and third trimesters of pregnancy.