Introduction:There are few studies regarding the treatment of vitamin D deficiency with a high dose of vitamin D and the comparison of serum vitamin D levels and hematological indices (Hemoglobin, Hematocrit, Platelet and Ferritin) in the first and second trimesters of pregnancy. The aim of this study was to evaluate the effect of vitamin D supplementation on these hematological indices in pregnant women with vitamin D deficiency.Materials and Methods: The present study was performed in October 2019 from a secondary and nonpredetermined analysis of the effect of vitamin D supplementation and comparison of serum vitamin D levels on blood parameters from a randomized controlled clinical trial. 215 pregnant mothers with vitamin D deficiency were entered in the study and were divided into two treatment groups of 50,000 units and 1000 units.Results: Mean serum levels of Hematocrit, Platelets, and Ferritin after treatment in the treatment groups with 50000 and 1000 unites were 38.6± 3.03 vs 36.05± 2.8 (P<0.38), 243083 ± 55302 vs 215942 ± 45513 (P<0.29) and 42.3± 33.5 vs 28.8± 21.7 (P<0.04), respectively. The mean Hemoglobin level in the treatment groups with 50,000 and 1000 units were 12.08± 1.17 vs. 12.3± 2.5 (P<0.84), respectively. In both groups, there was a significant relationship between serum vitamin D level, Hemoglobin and Hematocrit levels before treatment. (Respectively P<0.02, P<0.02 and P<0.05). The serum Ferritin level was significantly higher with serum vitamin D after treatment (P<0.04). Conclusion:This study showed that the results of two therapeutic groups in pregnant women with vitamin D deficiency, especially a dose of 50,000 units of vitamin D, compared to the first trimester of pregnancy, had different effects on the hematologic indices.