Alloimmunization and von Willebrand's Disease

Question 1

What are the most common causes of alloimmunization?

Answer 1

• abruption
• trauma
• SAB/TAB
• ectopic pregnancy
• chorionic villus sampling
• amnio
• external cephalic version

Question 2

How much blood is needed to induce alloimmunization?

Answer 2

<0.1cc

Question 3

What is the difference between direct and indirect Coombs test?

Answer 3

direct: checks for Abs attached to RBCs
indirect: checks for free Abs; what we draw in pregnancy

Question 4

What occurs in hemolytic disease of the fetus and newborn?

Answer 4

maternal anti-D IgG destroys fetal RBCs –> fetal anemia

Question 5

How is possible alloimmunization managed?

Answer 5

give 300mcg Rh immune globulin at 28wks GA –> neutralizes up to 30mL fetal whole blood, 15 mL fetal RBCs

Question 6

What is management of possible alloimmunization postpartum?

Answer 6

• Rosette test: detects >2mL fetal whole blood in maternal circulation –>
• Kleihauer Betke acid elution test: gives % fetal RBCs in maternal circulation –>

if fetal RBCs >30cc, give more RhoGAM

Question 7

What paternal genetic makeup determines Rh status in fetus?

Answer 7

• homozygous D Ag –> all children Rh+

- heterzygous D Ag –> 50% Rh+; 50% Rh-

Question 8

Describe incidence of von Willebrand’s disease

Answer 8

• most common inherited bleeding disorder
• Type 1 = most common; autosomal dominant
• Type 2, type 3 = recessive; less common

Question 9

What is the effect of pregnancy on von Willebrand factor?

Answer 9

• increased levels in pregnancy
• increased clotting factors –> improved bleeding time
• can present w/ delayed postpartum hemorrhage (>48h, usually 5-10 days) when levels fall

Question 10

What tests are used to dx VWD?

Answer 10

• CBC
• peripheral smear
• PT
• PTT
• PLT function activity (PFA-100)

*increased PTT and PFA-100 may be diagnostic of VWD

Question 11

What risks are associated w/ VWD?

Answer 11

clinical severity = variable

• menorrhagia
• easy bruising
• ginigival bleeding
• epistaxis
• bleeding during pregnancy = RARE
• PPH; w/ hx PPH, give IV desmopressin immediately PP and again 24h later
• no fetal effects

Question 12

How should pts w/ VWD be managed?

Answer 12

• type 1 rarely requires tx
• immunize for hep A and hep B in case of transfusion
• monitor clotting factor levels (NOB, 28wks, 34wks)
• refer to heme and interdisciplinary management