Alloimmune conditions and pregnancy.

Transfer of fetal red blood cells and platelets to the maternal circulation can stimulate an immune response with production of immunoglobulin that can cross the placenta. Similarly, passage of maternal stem cells to an immunologically incompetent fetus can theoretically produce graft-versus-host disease. disease. Maternal sensitization to red blood cell antigens such as D and Kell can result in anaemia, hydrops, and death in an incompatible fetus. Current assessment of these pregnancies involves serial analysis of amniotic fluid bilirubin concentration, with umbilical cord blood sampling reserved for special circumstances; neither ultrasound or Doppler blood flow analysis are accurate in the prediction of fetal haematocrit. Intravascular transfusion is the treatment of choice for hydropic fetuses. Perinatal survival in non-hydropic fetuses is similar with either intravascular or intraperitoneal transfusion, and the choice of procedures is individualized. Isoimmune fetal thrombocytopenia is usually the result of maternal sensitization to the PlA1 antigen. There is significant risk of intracranial haemorrhage, both antepartum and during labour and delivery. Umbilical cord blood sampling at term can determine fetal platelet count and the need for platelet transfusion, and can aid in deciding the appropriate route of delivery.