Introduction: Maternal RBC alloimmunization results from exposure and response to a foreign RBC antigen. Transplacental fetal to maternal hemorrhage is the most common cause of alloimmunization. Rh incompatibility can lead to either fetuses with hydropic features or non hydropic. The precise mechanism leading to the development of hydrops is not certain. All direct fetal sequelae of hemolytic disease relate to the development of anemia. In general, the fetus tolerates mild to moderate anemia well. However, metabolic complications develop as the anemia worsens. Because the RBC is the principal fetal buffer, a metabolic acidemia with hyperlactatemia develops in fetuses with severe anemia. Objective: To compare the difference in mean hemoglobin and hematocrit concentration between Rh-hydropic, non hydropic and control group and further based on severity of hydrops. Methods: A Total of 40 pregnant patients were enrolled which included 10 hydropic fetuses of Rh isoimmunised mothers, 10 non hydropic fetuses of Rh isoimmunized mothers. Control group included 18 Rh positive women without any fetal complication and 2 fetuses in women undergoing cordocentesis. Blood sampling was done at time of intrauterine transfusion and sent for estimation of hemoglobin and hematocrit in fetal blood. Pregnancies were followed up till delivery and fetal outcome noted. Result: Mean values of haemoglobin in hydrops group are 4.54g %, as compared to 6.65g % and 14.26 g % in non-hydrops and control group. Mean haematocrit in hydropic group is 13.91% as compared to 20.25% and 43.51% in non hydropic and control group. The mean haemoglobin concentration in mild hydrops was 5.17g % as compared to 2.7g % in severe hydrops. Conclusion: There was severe hemoglobin and hematocrit deficit in hydropic fetuses as compared to non hydropic and normal fetuses matched for the gestation age. Thus severity of anemia can be considered a strong marker for development of hydrops in Rh isoimmunized fetuses.