OBG- Rh isoimmunization PowerPoint presentation

Rh isoimmunization

1. Rh ISOIMMUNIZATION IN PREGNANCY Vani Sharma

2. Introduction Rh is an antigen found in the red blood cell Discovered by Landsteiner and Weiner in 1940 Person having Rh antigen is Rh-positive, and in whom it is not present, is Rh-negative Rh antigen helps to maintain erythrocyte membrane integrity.

3. Rh genotype The complete genetic make up of the Rh blood group of an individual is its genotype. The genetic locus for the Rh antigen complex is on the short arm of the first chromosome. Rh CcEe and RhD are the two distinct genes located within the Rh locus. Because of lack of proper antisera against anti-e, anti-c and anti-k the D antigen is the most potent Genotype Phenotype Antigen present DD Rh+ve D antigen Dd Rh+ve D antigen dd Rh- ve No D antigen

4. Rh isoimmunization Isoimmunization : Production of antibodies in response to an antigen derived from another individual of the same species, provided the first one lacks the antigen It has 2 phases : (1) sensitization, (2) immunization Occurs in case of: 1. Transfusion of mismatched blood, and 2. Pregnancy with Rh- ve mother and Rh+ve fetus

5. Pathophysiology 1st Rh+ve pregnancy: Rh- ve mother bearing Rh+ve fetus Normally, rare chance of fetal RBCs entering maternal circulation Feto -maternal bleed: Miscarriage MTP Genetic amniocentesis Ectopic pregnancy Hydatidiform mole Note: This is much more likely to occur during third stage of labor and following cesarean section or manual removal of placenta. Immunization is unlikely to occur unless at least 0.1 mL of fetal blood enters the maternal circulation. Not all “at risk” Rh-negative women become alloimmunized .

6. 1 st pregnancy: Father(Rh+ve) Mother(Rh- ve ) Fetus(Rh+ve) Subsequent pregnancies Father(Rh+ve) Mother(Rh- ve ) Fetus(Rh+ve) First newborn ( RhD +) SAFE But mother is now sensitized to Rh: IgM antibodies produced Later, IgG antibodies are formed Rapid production of IgG anti-D by mother Maternal IgG crosses placenta IgG anti-D attaches to fetal RBCs and cause their destruction Hemolytic disease of newborn

7. A ffection of the baby due to Rh incompatibility is low considering the increased number of Rh-positive babies delivered to Rh-negative mothers Possible reasons are: Insufficient placental transfer of fetal antigens or maternal antibodies. Inborn inability to respond to the Rh antigen stimulus. Immunological non-responder — as found in 30% of Rh-negative women. ABO incompatibility- ( i ) ABO incompatible fetal cells are cleared from the maternal circulation rapidly before they are trapped by the spleen (ii) maternal anti-A or anti-B antibodies damage the Rh-antigen so that it is no longer immunogenic. Volume of fetal blood entering into the maternal circulation

8. Mechanism of antibody formation Detectable antibodies usually develop after 6 months following larger volume of feto -maternal bleed As this takes a long time, immunization in a first pregnancy is unlikely. TYPES OF ANTIBODIES FORMED: IgM IgG First to appear Appears later Agglutinates D in saline Agglutinates D in 20% albumin Large; cannot cross placenta Small; can cross placenta Do not cause much harm to fetus May cause hemolytic disease of newborn

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