[Usefulness of erythropoietin in the treatment of anemia of prematurity.  Influence of birth weight]. 
Our objective was to analyze the utility of treatment with erythropoietin (EPO) plus iron in decreasing the need of late transfusions and reaching hematocrit > or = 32% in preterm infants of < or = 32 weeks of gestation.  Between March 1996 and October 1998, preterm infants of one unit were considered as the control group, while another group in another unit in the same hospital were treated with EPO (250 U/Kg, 3 times a week, subcutaneously) from day 7 of life until 37 weeks 37 post-conception.  Oral iron was added to treatment one week later (5 mg/Kg, and increased in order to keep ferritin levels > 100 ng/ml).  More strict transfusion criteria were established.  Weights were stratified in < 1,000 g, 1,000-1,249 g and > or = 1,250 g. Blood losses during the first 2 weeks were higher in the control group and that was probably the reason for the increased number of transfusions during the first 10 days of life.  Late transfusions decreased in the EPO treated group (p < 0.0003).  This was significant after the 3rd week and in the 1,000-1,249 g weight group.  The EPO-treated group showed lower hematocrit < or = 32% (p < 0.001).  When EPO-treated infants were separately analyzed it was clear that late transfusions were more frequent in infants that were smaller, more immature and sicker and with higher blood losses.  The reticulocyte count increase was similar in both groups of late transfused vs. Not transfused EPO-treated infants, being higher at 4 weeks after EPO was started (30/1000).  EPO and ferritin values were always higher in late transfused EPO-treated infants than in non-transfused infants.  The EPO plus iron treated group of preterm infants had a 40% decrease in the need for late transfusions in comparison with the control group.  The best results were obtained in the 1000-1249 g group of preterm infants.