Alloimmunization Flashcards
immune response to foreign antigen after exposure to different cells or tissues
alloimmunization
How can alloimmunization affect the fetus?
transplacental passage → hemolytic disease
most common 3 red blood cell alloimmunization that account for majority of fetuses with severe disease that require intrauterine transfusion for fetal anemia or cause hydropic still birth
anti D
anti c
anti Kell
what are two common factors of alloimmunization?
ABO compatibility and status of father
Rh D alloimmunization can be caused by a fetus with _____ and a mother with _____
Rh + erythrocytes
Rh - erythrocytes
in order for Rh D alloimmunization to occur a significant number of fetal erythrocytes must gain access to maternal circulation, how can this occur?
ectopic pregnancy surgery miscarriage D&C C-section delivery fetal maternal hemorrhage (placenta previa or abruption placentae)
What procedure increases the risk of maternal fetal hemorrhage? What should Rh-D negative mom get prior to procedure?
chorionic villus sampling
RhoGAM
what 3 conditions can result in Rh D alloimmunization?
- Rh (+) fetus in Rh (-) mom
- mom must have immunogenic capacity to produce antibodies against Rh D antigen
- significant number of fetal erythrocytes must gain access to maternal circulation
If breach of choriodecidual space is suspected, how soon should you administer RhoGAM?
within 72 hours
in subsequent pregnancies if a mother carries Rh (+) fetus, what affect can the anti Rh antibodies have on the fetus?
hemolytic anemia jaundice kernicterus hepatosplenomegally fetal hydrops
condition characterized by abnormal collection of fluid in the fetus
hydrops fetalis
at least 2 of the following are places were fluid abnormally collects and results in hydrops fetalis
edema (>5 mm)
ascites
pleural effusion
pericardial effusion
two classifications of hydrops fetalis
immune and nonimmune
what two things are hydrops fetalis frequently associated with?
polyhydramnios and thickened placenta (>6 cm)
common complaints of hydrops fetalis
polyhydramnios in thick placenta size is greater than dates fetal tachycardia (>160) decreased fetal movement abnormal serum screening antenatal hemorrhage
maternal antibodies against RBC of fetus cross the placenta and coat fetal RBC and destroy them
immune hydrops
severe anemia as a result of immune hydrops leads to….
high output CHF
liver and spleen increases RBC production → hepatic circulatory obstruction (Portal HTN)
hemolytic disease of newborn
any cause of hydrops fetalis that is not immune related → failure of interstitial fluid to return to the venous system
nonimmune hydrops
what are some causes of nonimmune hydrops?
cardiac failure
impaired venous retun
obstruction of normal lymphatic flow
increased capillary permeability
method used to screen for antibodies for anti D and other atypicals
indirect Coombs test
Indirect Coombs test indicates Rh (-) woman is alloimmunized to Rh D, what is the next step?
order anti-D titer → roughly correlates with disease severity
Doppler flow studies
Anti-D titer of ___ requires further assessment
1:16
If a titer is less than 1:16, how often should you follow them with titer?
monthly
preferred method and standard of care for monitoring fetal anemia
Doppler velocimetry of middle cerebral artery
As a fetus becomes more anemic, how will Doppler velocimetry change?
more anemic → decrease blood viscocity → increase velocity of flow through MCA
Prevention of alloimmunization of Rh
RhoGAM
How does RhoGAM work?
binds to fetal RBC and prevents maternal mixing
3 instances/indications where you would give Rh (-) and negative antibody screen RhoGAM?
- @ 28 weeks gestations
- with 72 hours of delivery
- potential mixing of blood
method to scree for fetal-maternal hemorrhage in routine situations begins with _____
rosette fetal red blood cell assay
inubate maternal sample with rh immunoglobulin that will bind fetal Rh-D (+) RBC → add enzyme treated reagent indicator RBC
rosette fetal RBC assay
Positve rosette test indicates Rh D (+) fetal RBC, what does positive test look like?
form aggregates (rosettes) visualized by light microscopy
Positive rosette tests should be followed by a method to determine percentage of fetal RBC in maternal ciruclation
Kleihauer Betke test
test to quantify amount of fetomaternal hemorrhage
Kleihauer Betke test
all pregnant women should be tested at time of first prenatal visit for ____ and ____ and screened for erythrocyte antibodies
ABO blood group and Rh D type
when should you repeat RhD antibody testing for all unsensitived Rh D (-) women?
24-28 weeks
ideal time to administer anti-D immune globulin
within 72 hours of potentially sensitizing event
ABO hemolytic disease due to incompatibilty is most pronounced in mother with blood type ___ and the father is ____
Mother → O
Father → A, B, or AB
predominant antibodies in mother with type O blood
IgG
what race is ABO hemolytic disease MC in?
African Americans
How is ABO disease unlike Rh?
ABO can occur in first pregnancy since anti A or B antibodies are found early in life
what will the fetus develop in ABO hemolytic disease within 24 hours?
jaundice
treatment for ABO hemolytic disease
usually none
how is ABO hemolytic disease less severe than anti-D sensitization?
less antibodies cross placenta
ABO antigens are in low numbers
fetal RBC are less developed at birth
presence of ABO antigens in tissues and secretions
these alloantibodies in pregnancy are known to suppress erythropoeisis → can result in serious disease despite low amniotic bilirubin levels and low antibody titers
Kell alloimmunization
how does anti-Kell autoantibodies impact fetal RBC?
fetal RBC destruction → erythroid precursor cells express Kell antigen → rapid and earlier development of fetal anemia
when severe Kell immunization occurs what is essential to prevent fetal death?
intrauterine blood transfusion
