7. Rhesus alloimmunization (Screening, exposure and prevention). "Hey guys Dr. Coore here let's talk rhesus alloimmunization. When the mother is rhesus D (antigen) negative and the fetus is rhesus D (antigen) positive, alloimmunization could occur and could cause catastrophic outcomes in the second pregnancy onward. Mothers produce Anti-D IgG (antibody) which crosses the placenta, lyses fetal red blood cells, causes significant anemia, high output cardiac failure and hydrops fetalis. So mothers are screened at the 1st antenatal visit and at 28 (to 32) weeks for anti-D (antibodies). If the screen is positive then no Anti-D Immune globulin is indicated. However if screens are negative, give the standard 300 micrograms at 28 weeks and at less than 72 hours postpartum if there is no worry of significant bleeds. In massive fetomaternal hemorrhage however, it's imperative to do the KB test (Kleihaur-Betke test) to decide how much more than 300 micrograms is indicated, remembering that 300 micrograms only cover for (neutralizes) up to 30mls of fetal blood." Also consider fetal extramedullary hematopoesis and hyperbilirubinemia and their complications as sequelae to rhesus alloimmunization.
A positive anti-D antibody screen means the horse has already gone through the door so to speak and maternal sensitization to the baby's foreign Rhesus D antigen has already happened!
A negative screen means no exposure has occurred, thus no maternal production of antibody could have taken place against fetal foreign rhesus D antigen, and so prophylaxis with anti-D immunoglobulin is necessary.
If hemorrhage is suspected, the rosette test, the initial test of choice, tells u if there is fetomaternal hemorrhage (FMH) or no whilst the KB test, the next step, quantifies the FMH. Flow cytometry needs expensive equipment and trained personnel though a great alternative.
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