HDFN Flashcards
Exam 4
How does Rhogam help to prevent the mother from making the anti-D antibody?
Rhogam contains anti-D which attaches to any fetal Rh positive RBCs in maternal circulation so the mother cannot be sensitized to them.
Why does Rh HDFN not usually affect the first pregnancy?
Many times the exposure to the D+ cells happens at birth. If it happens earlier, the initial antibodies produced by the mother are IgM and cannot cross the placenta to cause HDFN.
What is Erythroblastosis fetalis?
Anemia stimulates the bone marrow to produce RBCs at an accelerated rate. The release of immature red cells into circulation is referred to as Erythroblastosis fetalis.
What is Hydrops fetalis (or fetal hydrops)?
Since the bone marrow can’t produce red cells fast enough, the spleen and liver also increase RBC formation in hematopoietic tissues causing them to become enlarged. This leads to Hydrops fetalis which is an abnormal accumulation of fluid causing swelling including edema (fluid beneath the skin), ascites (fluid in the abdomen), and effusion (fluid around the lungs).
Describe the pathogenesis of hemolytic disease of the newborn from attachment of maternal antibody to fetal red cells to Hydrops fetalis.
Maternal IgG anti-D antibody crosses the placenta to the fetus and attaches to Rh(D)+ fetal red cells. The red cells are destroyed at an accelerated rate and the bone marrow attempts to produce more red cells at a faster rate. This causes the bone marrow to release immature red cells into circulation (erythroblastosis fetalis). Since the bone marrow can’t keep up, the liver and spleen also increase RBC production causing them to become enlarged. This leads to swelling and accumulation of fluid found in Hydrops fetalis.
How long will destruction of infant red cells continue after birth?
It will continue as long as maternal antibody persists. This is usually a couple weeks after birth since the half-life of IgG is 25 days.
What is kernicterus and why does it occur?
Kernicterus is toxic levels of bilirubin accumulation in the newborn’s brain. This occurs after birth. Before birth, the mother’s liver was removing the baby’s bilirubin from circulation. The newborn liver however, cannot conjugate bilirubin effectively causing it to accumulate in the newborn.
What factors affect the immunization and severity of HDFN?
Antigenic exposure, host factors, immunoglobulin class, antibody specificity, and influence of ABO group
What are some situations during which a mother may be exposed to fetal red cells?
Amniocentesis, cordocentesis, trauma to abdomen, birth
Which subclasses of IgG are most efficient at hemolysis and therefore most likely to cause HDFN?
IgG1 and IgG3
Which antibody is most clinically significant in HDFN after the D antibody? Why?
Anti-K. The K antigen is found on all precursor red cells as well as mature red cells. Therefore, not only are mature red cells being destroyed, but the immature red cells are also destroyed.
Why is a mother who has an ABO incompatible fetus less likely to experience D immunization?
ABO incompatible red cells are destroyed in the mother’s circulation before the D antigen can be recognized. There is therefore not enough time for sensitization to the D antigen to occur.
What blood type of the mother is the most likely to cause ABO HDFN? Why?
It is usually group O mothers because they make the antibody anti-A,B which is the only ABO antibody that is usually an IgG antibody that can cross the placenta.
What antibody is the most common cause of HDFN since Rhogam?
ABO
What are the common symptoms of ABO HDFN in the newborn?
Hyperbilirubinemia and jaundice 12-48 hours after birth. Rarely severe anemia
Describe how Rh HDFN differs from ABO HDFN.
ABO affects the 1st pregnancy, Rh the 2nd. Rh can be predicted by titers, ABO cannot. Bilirubin at birth is normal for ABO and elevated for Rh. There is no anemia at birth for ABO, there is for RH. Exchange transfusions and intrauterine transfusions are usually only used for Rh HDFN.
What testing is performed on a pregnant mother?
ABO, Rh, antibody screen, weak D if Rh negative, antibody titer if antibody screen is positive
What is the purpose of an antibody titer and when is it performed?
It determines the concentration of antibodies that is able to cross the placenta. It is performed each month during pregnancy to determine if the concentration of the antibody is increasing (suggesting the baby is positive for the antigen).
How often should titers be performed?
Once a month
At what point is a titer considered critical?
A titer of 16 is critical or an increase of 2 dilutions in one month
What additional information can be gained by phenotyping the father for the antigens the mother has an antibody to?
If the father is also negative, the fetus must be negative as well and HDFN is not a concern. If the father is positive, then there is a possibility the fetus is also positive for the antigen.
What does the MCA-PSV test determine and when would it be performed?
Predicts anemia in the fetus by detecting blood flow in the brain. It should be performed at 16-20 weeks if anemia is suspected.
What additional information is gained by performing a cordocentesis?
Blood can be taken from the umbilical cord and tested for hemoglobin, hematocrit, bilirubin, ABORh, DAT, and antigen phenotypes
What additional information is gained by performing an amniocentesis?
Measures concentration of bilirubin pigment in amniotic fluid estimating the extent of fetal hemolysis (really same information as MCA-PSV which is less invasive)
