Rh isoimmunization Flashcards
What is the physiology of red cell alloimmunization?
transplacental passage of maternal antibodies that destroy fetal red cells
- IgG crosses the placenta
- ABO incompatibility -> mild disease
- isoimmunization will get worse with successive pregnancy
When should screening be done?
- at booking & at 28 weeks -> blood group & antibody screen
- if mother is D negative -> husband blood group
- if antibody screen is positive is positive -> antibody titer should be quantified
What do the results of the antibody titer indicate?
< 4 IU/ml -> HDFN unlikely
4 - 15 IU/ml -> moderate risk of HDFN
> 15 IU/ml -> high risk of hydrops fetalis
What are the causes of red cell alloimmunization?
1- abortion
2- ectopic pregnancy
3- fetal death
4- amniocentesis
5- chorionic villous sampling
6- fetal blood sampling
7- external cephalic version
8- antepartum hemorrhage
9- vaginal or C section
10- trauma
How should a sensitized lady be managed?
1- dont give anti-D
2- repeat titer every 4 weeks
- if titer > 4 IU refer to fetal medicine unit for follow up
- if titer > 15 IU: middle cerebral artery doppler peak systolic velocity should be done to check for fetal anemia
When is fetal blood sampling indicated?
if MCA doppler exceed 1.5 MoM
for intrauterine blood transfusion
What are the features of Rh isoimmunization?
1- reduced fetal movement
2- anemia; increased MCA peak systolic velocity
3- polyhydramnios, enlarged heart, ascites, pleural effusion
4- abnormal CTG, reduced variability, sinusoidal pattern
When should intrauterine blood transfusions be preformed in case of increased MCA doppler?
done before 34 - 35 weeks
- through umbilical vein, hepatic vein, peritoneal cavity (early), or into the heart
when fetal hematocrit is <30%
- next transfusion should be scheduled every 2 - 4 weeks
- delay first transfusion after 20 weeks to decrease risk of still birth
What should be the characters of the blood transfused to the fetus?
O -ive
- CMV negative
- D negative
- packed to hematocrit of 80%
- leucocyte poor (to prevent fetal graft vs host reaction)
- cross matched with maternal sample
What are the outcomes of an intrauterine transfusion?
- survival rate is 95%
- may lead to emergency C section
- stillbirth
How is alloimmunization prevented?
1- give D negative mother anti-D Ig at 23 & 34 weeks
2- at delivery check if baby is positive then give mother anti-D within 72 hours
3- after any sensitizing event anti D should be given within 72 hours
What are the types of tests used for alloimmunization?
Rosette test
- qualitative
- identifies fetal cells in the circulation of negative lady even in small amounts
Kleihauer test
- quantitative
- important in large feto maternal hemorrhage to decide dose of anti-D
How is the needed dose of anti-D calculated?
IM of intramuscular dose of 1500IU or 300 micrograms
- covers 15ml of fetal RBCs & 30ml of fetal whole blood
- extra 300 microgram anti-D incase of any extra amount of fetal blood
When is referral indicated to fetal medicine unit?
- anti - D > 4
- anti K once detected
- anti C if >7.5 -> if > 20 IU indicates high risk for HDFN
How is hydrops fetalis diagnosed?
- presence of 2 or more effusions: pleural, ascites, pericardial
OR - 1 effusion & anasarca
- anasarca: skin thickness > 5mm, placental thickness >4cm in 2nd trimester & >6cm in 3rd trimester
