Alloimmunization

Question 1

When does alloimmunization most commonly occur?

Answer 1

At time of delivery (CS or NSVD)

45% of women experience fetal-maternal hemorrhage

Question 2

Is operative delivery a risk factor for fetal-maternal hemorrhage?

Answer 2

Nope!

Question 3

Timeline for administration of anti-D immune globulin?

Answer 3

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%)

Question 4

Most common ethnic group to Rh Neg?

Answer 4

White Race

Question 5

What amount of fetal blood is enough to cause alloimmunization in pregnancy?

Answer 5

Hemorrhage of as little as 0.1 mL

Question 6

Critical Ab titer for alloimmunization?

Answer 6

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

Question 7

Work up of positive ab screen

Answer 7

1. Identify antibody
2. Titer
3. Determine paternity testing/fetal status
4. 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)

Question 8

Define elevated MCA doppler

Answer 8

> 1.5 MOM

Sensitivity 88%
Specificity 82%
Accuracy 85%

Question 9

Management of elevated MCA doppler?

Answer 9

PUBS (percutaneous umbilical cord sampling)

If fetal HCT is < 30% proceed with intrauterine transfusion

Question 10

If fetus is requiring intrauterine transfusion… when should it be delivered?

Answer 10

34 weeks

Question 11

How much fetal blood does 1 dose (300 mcg) of Rhogam cover?

Answer 11

30 cc of WHOLE fetal blood (15 cc of RBCs)

Question 12

`Most likely exposure to Kell antigen?

Answer 12

Previous blood transfusion (kell compatibility is not part of routine screening)

Question 13

Giving Rhogam within 72 hours event reduces the risk of alloimmunization by how much?

Answer 13

80-90%

Question 14

Do WEAK D moms need rhogam?

Answer 14

Yes!!
Candidates for Rhogam

However, in the setting of blood transfusion considered Rh Neg

Question 15

Max dose of Rhogam?

Answer 15

8 vials

Question 16

How long does Anti-D immune globulin appear to persist for in most patients?

Answer 16

12 weeks

Question 17

The typical third-trimester prophylactic dose of anti-D immune globulin protects against exposure of up to how much fetal whole blood?

Answer 17

30 mL WHOLE BLOOD

15 ml RBCs

Question 18

Kell Antigen

Answer 18

K1 (BIG K)

Little k is OK (so if father is kk, then fetus is unaffected)

Question 19

Kell Management

Answer 19

• Assess paternal status

- If positive fetus should be monitored w/ MCA dopplers Q2 weeks starting at 18w to 35 wks

Question 20

MCA dopplers after what gestational age are no longer accurate?

Answer 20

35 weeks

Question 21

Most common antigen in Neonatal Alloimmune Thrombocytopenia

Answer 21

HPA-1a

Results in severe thrombocytopenia (< 20k)

Can cause intracranial hemorrhage while in utero and in the neonatal period

Question 22

Is maternal platelet count affected by neonatal alloimmune thrombocytopenia?

Answer 22

Nope! Usually normally

Question 23

Presenting sign of neonatal alloimmune thrombocytopenia?

Answer 23

Generalized petechiae or ecchymosis

Continued bleeding after circumcision
ed
Seizures from intracranial hemorrhage

Question 24

Risk of recurrence of neonatal alloimmune thrombocytopenia?

Answer 24

Nearly 100% of all future pregnancies between the couple will be affect

Question 25

Treatment for neonatal alloimmune thrombocytopenia?

Answer 25

Weekly IVIG starting at 12 or 20 weeks

Consider prednisone

Question 26

Do you check titers for Kell antibody?

Answer 26

NO! Just go straight to MCA Dopplers Q2 weeks from 18w-35w

Question 27

Most common cause of severe thrombocytopenia in term newborns?

Answer 27

Alloimmune thrombocytopenia