Immune conflict at pregnancy Andrii Berbets, assist.prof
Isoimmunization• Isoimmunization can involve many of the several hundred blood group systems.• This disorder is frequently referred to as Rh isoimmunization, because the Rhesus (Rh) system is most frequently involved. For the sake of this discussion, the Rh system will be used as an example, although it should be remembered that isoimmunization can and does develop with many other blood systems such as Kell, Duffy, Kidd, and others.
• Rhesus (Rh) isoimmunization is an immunologic disorder that occurs in a pregnant, Rh-negative patient carrying an Rh- positive fetus. The immunologic system in the mother is stimulated to produce antibodies to the Rh antigen, which then cross the placenta and destroy red blood cells.
Pathophysiology• The “Rh disease ” results from the Rh negative mother becoming isoimmunized to an Rh antibody from the red cells of her first child.• The first Rh positive pregnancy is almost never affected unless the mother has had a previous blood transfusion with Rh positive blood;• Once immunized, the mother’s immune system responds by manufacturing anti Rh isoantibodies with a second pregnancy;• If the second pregnancy is one in which the fetus is Rh positive, the mother’s anti Rh Isoantibodies are transferred to the fetus across the placenta.
Pathogenesis• If the mother produces immunoglobulin M (IgM)-type antibodies, the molecules do not cross the placenta, because they are too large. In the case of Rh factor, however, the maternal antibody is predominantly the smaller IgG- type, which can freely cross the placenta and enter the fetal circulation.
Pathogenesis• The antibody attaches to the Rh+ red blood cells and hemolyzes them. The bilirubin produced in this hemolytic process is transferred back across the placenta to the mother and metabolized. The condition of the fetus is determined by the amount of maternal antibody transferred across the placenta and the ability of the fetus to replace the red blood cells that have been destroyed.
DIAGNOSIS History. Laboratory evaluation include such methods of diagnostics as: Maternal blood is tested for presence of a variety antibodies – “antibody screening test”, “indirect” and “direct Coomb’s tests”.• Mild isoimmunization – antibody titer below 1:16. Rarely produce fetal hydrops and usually do not require any intervention in the pregnancy. The newborn may be anemic and develop hyperbilirubinemia.• Severe isoimmunization - titer of over 1:16 or greater is generally considered the critical point at which there is sufficient risk of fetal jeopardy to warrant additional evaluation. This should be done amniocentesis or percutaneous umbilical blood sampling (PUBS).• Determination of the fathers Rh status is extremely helpful.• Amniocentesis denotes the amount of blood destruction by estimating the amount of bilirubin pigments in the amniotic fluid;
Indications to amniocentesis are:• 1) Antenatal fetal death and isoimminization in previous pregnancies;• 2) Hemolytic infant disease in the previous pregnancies;• 3) Increasing of antibodies titer to 1: 32. Contraindications to amniocentesis are:• Threatened abortus and preterm labor;• Fever;• Abnormal uterine development.
• Amniotic fluid spectrophotometry – there is an excellent correlation between the amount of biliary pigment in the amniotic fluid and the fetal hematocrit beginning at 27 weeks’ gestation.• Liley chart can be used – it is a spectrophotometric graph based on the correlation of cord blood hemoglobin concentrations at birth and the amniotic fluid change in optical density at 450m.
• Amniotic fluid assessment is of great value in managing the isoimmunized patient.• The level of bilirubin in the amniotic fluid accurately reflects the condition of the fetus. The level of bilirubin in the amniotic fluid is determined using a spectrophotometer.• Normal amniotic fluid subjected to spectrophotometric analysis has a characteristic curve, based on optical density (OD). The presence of bilirubin causes a characteristic deviation in this curve, at 450 nm.
Optical density of the amniotic fluid Optical density (green Concentration of Risk of hemolyticlight with the wave 450 bilirubin in amniotic disease of fetus nm) fluid, mg/l 0,15-0,20 0-2,8 Low 0,21-0,34 2,9-4,6 Moderate 0,35-0,70 4,7-9,5 High More 0,70 More 9,5 Very high
Cordocentesis• Percutaneous umbilical blood sampling (PUBS) under ultrasound guidance – fetal blood can be taken for hematocrit, hemoglobin, blood gases, pH, bilirubin levels
In specializing obstetrics department: Plasmapheresis should be started from early terms of pregnancy gestation under controll antibodies titer every two weeks. The course of treatment include 4-5 times of plasmopheresis with interval 1-2 days. Such method of treatment eliminates circulating immune complexes, and antibodies.
Kernicterus - brain damage caused by bilirubin• Most biliribin is bound to albumin in the newborn’s blood. When the concentration of bilirubin in the newborn blood exceeds in-term fetus – 307,8 – 342 mkmoll/L, in pre-term fetus – 153-205 mkmoll/L, the albumin binding sites are all filled, and bilirubin molecules are then freed to enter the tissues.• Biliribin is a cytological poison, nad it is a preferentially taken up by the cells of the basal ganglia. When a sufficient number of basal ganglia neurons are damaged by the larger amount bilirubin, the function of the basal ganglia is destroyed.• The clinical picture is one of motor handicap (similar to cerebral palsy).
Pregnant women undergo cesarean section in such cases as: – Severe form of hemolytic infant disease in the term 34-35 weeks after previous antenatal prevention of fetal hyaline membranes syndrome; – Hydrops fetalis in any gestation term because of interm pregnancy would provoke antenatal fetal death.
Stages of hemolytic disease of infant severity I stage II stage III stageClinical symptomAnemia, hemoglobin 150 150-100 100level in umbilical cord(g/L)Jaundice, bilirubin level 85,5 85,6-136,8 136,9in umbilical cord(mkmol/L)Edema Subcutaneous Edema of Hydrops edema subcutaneous fetalis fat and ascites
Indications to exchange blood transfusion in infants In -term fetus : Pre-term fetus Laboratory symptom 1 day Repeated 5 day 1 day Repeate 5 day dIndirect bilirubin, > 68,42 300,7 59,9 273,6mkmoll/LIndirect bilirubin per 6,8 6,8 5,1 5,1hour, mkmoll/LHemoglobin, g/L < 150 < 150Hematocrit <0,4 < 0,4
Prevention• administration RhoGAM (Rh immune globulin) soon after delivery could, by passive immunization, prevent an active antibody response by the mother in most cases.• Rh immune globulin is effective for only the D antigen of the Rh system. No similar preparations are available for patients sensitized with the many other possible antigens.• It is now standard practice for Rh- patients who deliver Rh+ infants to receive an intramuscular dose of 300 mkg of Rh immune globulin (i.e., RhoGAM) within 72 hours of delivery.
Indications of RhoGAM administration in a n Unsesitized Rh-negative patient (unless the father of the infant is known to be Rh-):• at approximately 28 weeks’ pregnancy – reduce the risk of sensitization to 0.2 %;• within 3 days ( 72 hours of delivery) days of delivery of an Rh-positive infant – the risk of subsequent sensitization decreases from approximately 15 % to 2 %;• at the time of amniocentesis;• after positive Kleihauer-Betke test - allows the identification of fetal cells in maternal circulation in cases of trauma or bleeding during pregnancy to which fetomaternal hemorrhage has occurred.;• after ectopic pregnancy, spontaneous or induced abortion – 50 mg of RhoGAM can be used to prevent sensitization.
NONRHESUS BLOOD GROUP ISOIMMUNIZATION• ABO hemolytic disease and non-Rh D/non-ABO hemolytic disease are rela-tively more common.• ABO hemolytic disease is associated with milder fetal kernicterus and, rarely, hydrops, probably because of the relatively smaller number of A and В antigenic sites on fetal red blood cells and because anti-A and -B are IgM and thus do not traverse the placenta well; that which does cross has a high propensity for other binding sites besides fetal red blood cells. This disease usually occurs in the first pregnancy, and amniocentesis and early delivery are rarely indicated.• Non-Rh D/non-ABO hemolytic diseaseis frequently associated with blood transfu-sion, because "compatible" blood transfu-sion is matched only to the ABO and Dd antigens. Pregnant women who are affected by the common and uncommon antibodies that can cause hemolytic disease of the new- born are managed in the same way as those who are Rh-. Those women with antibodies that are very rarely or unassociated with hemolytic disease of the newborn need not be treated.