Alloimmunization Flashcards
When does alloimmunization most commonly occur?
At time of delivery (CS or NSVD)
45% of women experience fetal-maternal hemorrhage
Is operative delivery a risk factor for fetal-maternal hemorrhage?
Nope!
Timeline for administration of anti-D immune globulin?
With in 72 hours of inciting event:
- SAB (1.5-2%)
- TAB, threatened ab (3-11%)
- bleeding previa
- abruption
- Amnio, CVS
- Ectopic pregnancy
- Molar pregnancy evacuation
- Abdominal trauma
- IUFD
- ECV (2-6%)
Most common ethnic group to Rh Neg?
White Race
What amount of fetal blood is enough to cause alloimmunization in pregnancy?
Hemorrhage of as little as 0.1 mL
Critical Ab titer for alloimmunization?
1 in 8 to 1 in 32
1 to 1 is undetectable/low titer, think of this as a dilutional measure- the higher the denominator, the higher amount of antibody present
Work up of positive ab screen
- Identify antibody
- Titer
- Determine paternity testing/fetal status
- If significant ab, and fetus at risk > trend titers Q4 wks
If “critical” threshold is reached (1 in 8 to 1in 32) then proceed with weekly MCA dopplers (Kell kills, doesn’t apply to K antibody)
Define elevated MCA doppler
> 1.5 MOM
Sensitivity 88%
Specificity 82%
Accuracy 85%
Management of elevated MCA doppler?
PUBS (percutaneous umbilical cord sampling)
If fetal HCT is < 30% proceed with intrauterine transfusion
If fetus is requiring intrauterine transfusion… when should it be delivered?
34 weeks
How much fetal blood does 1 dose (300 mcg) of Rhogam cover?
30 cc of WHOLE fetal blood (15 cc of RBCs)
`Most likely exposure to Kell antigen?
Previous blood transfusion (kell compatibility is not part of routine screening)
Giving Rhogam within 72 hours event reduces the risk of alloimmunization by how much?
80-90%
Do WEAK D moms need rhogam?
Yes!!
Candidates for Rhogam
However, in the setting of blood transfusion considered Rh Neg
Max dose of Rhogam?
8 vials
How long does Anti-D immune globulin appear to persist for in most patients?
12 weeks
The typical third-trimester prophylactic dose of anti-D immune globulin protects against exposure of up to how much fetal whole blood?
30 mL WHOLE BLOOD
15 ml RBCs
Kell Antigen
K1 (BIG K)
Little k is OK (so if father is kk, then fetus is unaffected)
Kell Management
- Assess paternal status
- If positive fetus should be monitored w/ MCA dopplers Q2 weeks starting at 18w to 35 wks
MCA dopplers after what gestational age are no longer accurate?
35 weeks
Most common antigen in Neonatal Alloimmune Thrombocytopenia
HPA-1a
Results in severe thrombocytopenia (< 20k)
Can cause intracranial hemorrhage while in utero and in the neonatal period
Is maternal platelet count affected by neonatal alloimmune thrombocytopenia?
Nope! Usually normally
Presenting sign of neonatal alloimmune thrombocytopenia?
Generalized petechiae or ecchymosis
Continued bleeding after circumcision
ed
Seizures from intracranial hemorrhage
Risk of recurrence of neonatal alloimmune thrombocytopenia?
Nearly 100% of all future pregnancies between the couple will be affect
Treatment for neonatal alloimmune thrombocytopenia?
Weekly IVIG starting at 12 or 20 weeks
Consider prednisone
Do you check titers for Kell antibody?
NO! Just go straight to MCA Dopplers Q2 weeks from 18w-35w
Most common cause of severe thrombocytopenia in term newborns?
Alloimmune thrombocytopenia
