13 - Rhesus Isoimmunization

Question 1

Rh incompatibility causes the fetal antigens to produce maternal antigens. The antibodies are:

Answer 1

1– Initially IgM [Cant cross the placenta]

2– After 6 weeks IgG [Can cross the placenta]

Question 2

The Rh incompatibility process in 4 steps:

Answer 2

1– Fetal RBCs enter maternal circulation [Fetomaternal hemorrhage]
2– Antibodies to D antigen [Anti-D] are produced [Sensitization]
3– Anti-D crosses the placenta in the next pregnancy
4– Fetal Rh +ve RBCs are destroyed by immune system [Sequestration by macrophages in fetal spleen and then hemolytic fetal anemia]

Question 3

Placenta acts as a barrier to fetal blood entering the maternal circulation, how can it enter the maternal circulation and cause the Rh incompatibility?

Answer 3

Fetal cells enter through a break in the placental barrier

Question 4

Break in the placental barrier causes:

Answer 4

1– Abortion 
2– Ectopic pregnancy 
3– Partial molar pregnancy 
4– Blighted ovum
5– Antepartum bleeding
6– Amnio/Cordocentesis 
7– Platelet transfusion 
8– Rh+ blood transfusion  
9– Postpartum [Rh+ baby]
10– Trauma

Question 5

Sensitization risk depends on 3 factors:

Answer 5

1– Volume of trans placental hemorrhage
2– Maternal immune response
3– Whether the mother has a protective factor for the ABO incompatibility in the first place

Question 6

The test to test for the Rh factor and when to test:

Answer 6

1– Indirect coomb’s test

2– Before 28 weeks

Question 7

S&S for Rh incompatibility:

Answer 7

— Mild anemia —> Jaundice [In mild cases] and Severe anemia —> Hypoxia, CVS failure [HF], edema, ascites —> IUFD [In severe cases]

— Excess UC bilirubin passes BBB —> Kernicterus —> Mental disorder

Question 8

Sign for obvious fetal anemia:

Answer 8

If fetal Hb <6 then the features of anemia can be seen

Question 9

Signs of fetal anemia:

Answer 9

1– Polyhydrominos 
2– Large heart
3– Ascites and pericardial effusion
4– Hyperdynamic fetal circulation
5– Reduced fetal movements 
6– Abnormal CTG [Low variability]

Question 10

Kleinhauer-Betke test:

Answer 10

% of fetal RBC in maternal circulation, if positive then give more Anti-D doses

Question 11

Anti-D doses:

Answer 11

— <20 wk —> 250 IU
— >20 wk —> 500 IU
— Postpartum —> 500 IU

Question 12

Test used to test the presence of RhD genes in both parents before pregnancy:

Answer 12

PCR

Question 13

Critical titer:

Answer 13

Titer ass. with a risk of fetal hydrops and its between 8–32

Question 14

First alloimmunization pregnancy with Rh+ fetus procedure:

Answer 14

AB titers are determined every 2–4 wks after 20 wks of GA as long as its below the critical titer

Question 15

The test used to assess for the severity of fetal anemia:

Answer 15

1– Middle cerebral artery-Peak systolic velocity [Using Doppler]
2– Fetal blood sampling [U/S directed through cordocentesis to check hematocrit, blood type, RBC count and platelet count]
3– Spectral analysis of amniotic fluid [Checking for bilirubin through amniocentesis] NOT USED

Question 16

TT:

Answer 16

Delivery [If mature [36–37]] or fetal blood transfusion

Question 17

Fetal blood transfusion route:

Answer 17

A— Umbilical vein through the placenta [NOT AMNIOTIC SAC]
B— Intrahepatic vein
C— Fetal heart

Question 18

Criteria for the transfused blood:

Answer 18

1– RhD -ve
2– Match the mother
3– Densely packed [Hb is 30]
4– WBCs depleted