Fetal Disorders and Anomalies w/out Genetics Flashcards
(346 cards)
How do you define alloimmunization?
Immune response to foreign antigens from another human
What is an indirect Coomb’s test?
Antibody screen in serum
What are possible sources of allommunization to the D antigen group?
Prior fetus with Rh+ antigen
Prior blood transfusion
What red cell antigens comprise the Rh antigen group?
C c D E e
What is Du antigen, and do you give rhogam?
Weak D antigen, yes we still give rhogam
What are the fetal risks in an alloimmunized pregnancy?
fetal anemia
hydrops
death
erythroblastosis fetalis
What is the cause of fetal anemia in an alloimmunized pregnancy?
Antibodies against fetal antigen that are destroying fetal RBCs
What is hemolytic disease of the newborn?
Hemolysis and anemia in the fetus due to Fetal RBC distruction by maternal alloantibodies that have crossed into the fetal circulation
When a positive antibody screen is identified, what are the next steps in your evaluation of the patient?
History to see if exposed
Paternal testing to assess risk
Fetal testing to assess risk
Serial titers until critical titer is reached (every 4 weeks)
MCA Dopplers once critical titer is reached
What is the mode of inheritance of red cell antigens?
Autosomal dominant for Rh
Co-dominant for ABO
When do RBC antigens first appear?
38 days
How likely is a Rh negative woman to get sensitized without rhogam?
What if she gets Rhogam postpartum?
What if she gets Rhogam at 28 weeks and postpartum?
16%
- 6%
- 16%
How much blood exposure does one 300mcg Rhogam protect you from?
30mL
What is a Kleihauer betke?
Maternal blood in acid elution, moms cells destroyed by Acid, HbF identified with stain.
Calculate % of fetal cells to maternal cells. Mutiply by 50, divide by 30 and thats how many vials of rhogam to give
If the father of the baby is homozygous for red cell antigen of interest, what is the likelhood of the fetus being at risk for hemolytic disease of the newborn?
What if the father is heterozygous?
Homozygous: 100%
Heterozygous: 50%
How can you determine fetal red cell antigen status?
Cell free DNA, Amniocentesis
If the fetal red cell antigen status is unknown, how will you follow the patient if this is her first alloimmunized pregnancy?
Can do paternal antigen testing, if negative and paternity is 100%
No further testing
If paternal testing is positive then monthly titers until she reaches critical titer
If the fetal red cell antigen status is unknown, how will you follow the patient if this is a subsequent alloimmunized pregnancy?
In a previously affected fetus, just skip to MCA Dopplers every 1-2 weeks starting at 16-18 weeks.
What is the role of antibody titers in a first alloimmunized pregnancy?
First alloimmunuzed pregnancy: Assess for a critical titer and the need for MCA testing for anemia
Subsequent alloimmunuzed pregnancy: No role for titers
What do you consider to be a critical antibody titer?
1:16 or higher
Once a critical antibody titer is identified, how does your management change?
Start MCA Doppler velocimetry weekly assessing for anemia and also evaluating for fetal hydrops
How do MCA Dopplers identify anemia?
As anemia worsensblood is less viscous and gets shunted to brain
Net result is an increased in the velocity of flow in MCA
Describe how you perform an MCA Doppler PSV assessment?
MCA near its origin Side closer to probe No fetal movement / breathing Zero angle of approach (no angle correction) Circle of willis visible 3 measurements, use the highest value
What does an MCA PSV >1.5MoM indicate?
Suggestive of fetal anemia