[Blood volume calculation required for the correction of fetal anemia in pregnant women with alloimmunization]. / Cálculo do volume de sangue necessário para a correção da anemia fetal em gestantes isoimunizadas.

PURPOSE: to obtain an equation to estimate the volume of red blood cells concentrate to be infused to correct anemia in fetuses of pregnant women with Rh factor isoimmunization, based in parameters obtained along the cordocentesis previous to intrauterine transfusion. METHODS: a transversal study analyzing 89 intrauterine transfusions to correct anemia in 48 fetuses followed-up in the Centro de Medicina Fetal do Hospital das Clínicas da Universidade de Minas Gerais. The median gestational age at the cordocentesis was 29 weeks and the average number of procedures was 2.1. Fetal hemoglobin was assayed before and after cordocentesis, leading to the volume of transfused red blood cells concentrate. The determination of an equation to estimate the blood volume necessary to correct the fetal anemia was based in the blood volume necessary to raise the fetal hemoglobin in 1 g% (the difference between the final and the initial hemoglobin concentration divided by the transfused volume) and in the volume of the amount necessary to reach 14 g%, in the multiple regression analysis. RESULTS: the concentration of pre-transfusion hemoglobin varied between 2.3 and 15.7 g%. The prevalence of fetal anemia (Hb<10 g%) was 52%. The regression equation obtained in the determination of blood volume necessary to reach the concentration of 14 g% of Hb was: transfusion volume (mL)=18.2 - 13.4 x pre- intrauterine transfusion hemoglobin + 6.0 x gestational age in weeks. This equation was statistically significant (p<0.0001). CONCLUSIONS: the study has shown that it is possible to estimate the transfusion volume necessary to correct fetal anemia, based on easily obtainable parameters: gestational age and level of pre-transfusion hemoglobin.