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OBJECTIVE: We report the outcome of pregnancies treated with intravenous immunoglobulin (IVIG) for severe red blood cell alloimmunization, evaluating whether IVIG defers the development of severe fetal anaemia and its consequences. BACKGROUND: Although fetal anemia can be treated very successfully with intrauterine transfusion (IUT), procedures before 20 weeks' gestation can be very challenging technically and may be hemodynamically stressful to an extremely premature and already compromised fetus. The procedure-related fetal loss rate is approximately 5.6% for IUTs performed < 20 weeks' gestation, compared to 1.6% overall. IVIG may prevent hemolysis and could therefore be a noninvasive alternative for early transfusions. STUDY DESIGN: We included consecutive pregnancies over a nineteen year period in the Fetal Medicine Unit, Mount Sinai Hospital, University of Toronto, Canada, of alloimmunized women with a history of severe early onset haemolytic disease who received IVIG until intrauterine transfusion could safely be performed. Previous untreated pregnancies were used as controls. IVIG therapy was commenced between 11 and 14 weeks' gestation. Our usual protocol was IVIG 2 g/kg per week every 3 weeks, until the first IUT could be performed. Each 2g/kg dose was administered over 2 days, 1g/kg per day, to reduce the chance of severe headaches. In three pregnancies, IVIG 1g/kg was given weekly. We compared the clinical outcomes (gestation at first IUT, fetal Hb at first FBS, gestation at delivery, perinatal survival) between previous pregnancies without IVIG and the subsequent pregnancy treated with IVIG. In comparing fetal Hb's between two pregnancies, a linear relationship between fetal Hb and gestation was used to correct for variable gestations. The fetal Hb was converted to a standardized fetal Hb value (multiples of the standard deviation [SD]). Statistical analysis was performed on 'Statistical Package for Social Science Version 16.0' (SPSS Inc, Chicago, Illinois). RESULTS: Seventeen women referred to our unit for a previous pregnancy loss secondary to severe RBC alloimmunization received IVIG treatment in 20 subsequent pregnancies; all eventually requiring intrauterine transfusion. For previous early losses despite transfusion, immunoglobulin was associated with a relative increase in fetal hemoglobin between treated and untreated pregnancies of 32.6 g/L (95%CI 15.2-50.0, P=0.003) and improved perinatal survival (8/8 vs 0/6, P=0.001). For previous losses CONCLUSION: Our results show that, among severely sensitized cases with previous early fetal loss despite IUT, use of IVIG in subsequent pregnancies is associated with a significantly higher fetal Hb before first IUT, deferral of first IUT, delivery at a later gestation and increased perinatal survival. The timing of the first FBS/IUT was delayed by 3 weeks in pregnancies treated with IVIG compared to a previous untreated pregnancy. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.