Megaloblastic anaemia is a disorder of the bone marrow. There is a presence of erythroblasts in the bone marrow with delayed nuclear maturation because of defective DNA synthesis.

In megaoblastic anaemia Erythrocytes are larger and have higher nuclear-to-cytoplasmic ratios compared to normoblastic cells.
Neutrophils can be hypersegmented, and megakaryocytes are abnormal. Risk Factors for Megaloblastic anaemia are Vitamin B12 deficiency ,Folic acid deficiency and Conditions with neither B12 nor folate deficiency, e.g. orotic aciduria, where there is a defect in pyrimidine synthesis, therapy with drugs interfering with DNA synthesis and myelodysplasia.