Rh alloimmunization

1. Alloimmunization

2. Objectives
1. Describe the pathophysiology and diagnosis of
alloimmunization
2. Describe the use of immunoglobulin prophylaxis during
pregnancy for the prevention of alloimmunization
3. Discuss the management of a patient with Rh-D
sensitization in pregnancy

3. Teaching Case
A 32 year-old P1101 woman and her new husband present for prenatal care
at 20 weeks gestation. Her past obstetric history is significant for a first
child delivered at term following an abruption. Her second child died of
complications of prematurity following in utero transfusions for Rh
alloimmunization. Her initial prenatal labs this pregnancy indicate her blood
type as A negative and an antibody screen positive for anti-D with a titer of
1:256. You discuss any additional evaluation needed, her risks in this
pregnancy, and the plan of management with her and her husband.

4. Teaching Case Cont.
1. What is Rh alloimmunization and what are the red cell antigens
involved?
2. What are the risk factors for Rh alloimmunization?
3. What is the mechanism for RhoGAM prophylaxis against Rh disease?
What is the dose of RhoGAM? What is the recommended schedule for
RhoGAM administration?
4. Could this patient’s Rh alloimmunization have been prevented? What
are the ways in which alloimmunization might be diagnosed? Is there
any further blood work that should be obtained before you counsel this
patient on her risks in this pregnancy? What are some ultrasound
findings that may suggest Rh disease?

5. 1. Pathophysiology of
Alloimmunization
- Normal: Maternal IgG antibodies can cross
the placenta and provide the fetus with
passive immunity following birth.
- However, antibodies could be directed at
antigens on fetal cells.
- Mostly minor (Rh and others) antigens are
targeted.
- usually little IgG directed at major A
and B antigens, so maternal-fetal ABO
incompatibility is usually nonexistent
or mild.

6. 1. Pathophysiology of
Alloimmunization
- Most cases are due to antibodies to the "D" antigen, termed "Rh Positive."
- The Rh negative mother forms antibodies on exposure to fetal Rh positive RBCs.
- However, antibodies may also be directed at other Rh antigens and other minor blood
group antigens such as:
- antigens of the Rh blood group system (c, C, e, E), anti-Kell (ie, K, k), anti-Duffy
(ie, Fya
), and anti-Kidd (ie, Jka
, Jkb
).

7. 1.Hemolytic Disease of the
Fetus/Newborn (HDFN)
- The crossing of the maternal anti-RhD antibodies through the
placenta to the fetus causes opsonization of fetal RBCs, leading
to phagocytosis by macrophages in the fetal spleen,
- This results in fetal anemia
- Fetal hydrops: diffuse edema, pleural and/or pericardial
effusions, and ascites
- Neonatal jaundice

8. 1. Diagnosis of Alloimmunization
- A critical titer for severe erythroblastosis fetalis and hydrops in most centers
is between 1:8 and 1:32. If the initial antibody titer is 1:8 or less, monitor
patient’s titers every 4 weeks.
- Screen for maternal alloantibodies through an Indirect Coombs test at:
- 1. First prenatal visit,
- 2. 28 wks EGA,
- 3. any potential hemorrhage events intrapartum
- 4. Postpartum.

9. 1. Diagnosis of Alloimmunization
Further Testing
- Paternal antigen status to assess
fetal risk through direct genotype
testing of the father
- If there is no access to paternal
genes, genetic analysis of fetal
DNA through amniocentesis or
cell free DNA in maternal blood
- Ultrasound for signs of severe
fetal anemia
- elevated peak velocity of the
middle cerebral artery
- hydrops fetalis
- Spectral Analysis of Amniotic
Fluid

10. - To prevent alloimmunization, when fetal-maternal hemorrhage may occur
causing exposure of fetal RBC antigens to the maternal immune system, the
product RhoGAM can be given.
- Rho(D) immune globulin consists of IgG anti-D antibodies that will bind the fetal
RBC D antigens circulating in the maternal blood
- This prevents the mother’s immune system from sensitizing to the antigen and
generating its own endogenous anti-D antibodies.
2. Immunoglobulin Prophylaxis

11. - Dosage: ~10 mcg/mL fetal blood
- 300 micrograms of anti-D immune globulin can prevent Rh D
alloimmunization after an exposure to up to 30 mL of Rh D-positive blood or
14-15 mL of fetal red blood cells
- Measure amount of maternal exposure to fetal blood through
Kleihauer-Betke test or flow cytometry
2. Immunoglobulin Prophylaxis

12. - First 300 mcg dose at 28 week EGA
- Second 300 mcg dose should be given
if delivery has not occurred within 12
weeks of the initial dose (at 40 weeks
EGA)
- Within 72 hours after delivery of an
Rh+ neonate
2. Immunoglobulin Prophylaxis
- After first trimester pregnancy loss,
threatened abortion, or elective
termination
- After invasive antepartum procedures
- Following external cephalic version or
trauma
- After second or third trimester
bleeding
- Placenta previa, abruption
- Multifetal gestation

13. 3. Management of Rh-D
Sensitization in Pregnancy
- Anti-D immune globulin is indicated only in Rh-negative women who are not
previously sensitized to D
- According to UpToDate: “Performing serial combined maternal plasmapheresis
and intravenous immune globulin therapy is a promising approach for decreasing
the severity of fetal disease when there is a significantly elevated titer (eg,
>1:256) or a history of previous severe hemolytic disease of the fetus and
newborn”
- Increased testing and patient follow ups for management of fetal anemia
- In Mild Anemia: Ultrasounds (MCA-PSV) and Serial titers
- In Severe Anemia: confirmed by fetal blood sampling for H/H
- <35 wks EGA, intrauterine fetal transfusions
- >35 weeks, delivery with neonatal care

14. Teaching Case
A 32 year-old P1101 woman and her new husband present for prenatal
care at 20 weeks gestation. Her past obstetric history is significant for a
first child delivered at term following an abruption. Her second child died
of complications of prematurity following in utero transfusions for Rh
alloimmunization. Her initial prenatal labs this pregnancy indicate her
blood type as A negative and an antibody screen positive for anti-D with a
titer of 1:256. You discuss any additional evaluation needed, her risks in this
pregnancy, and the plan of management with her and her husband.
1. What is Rh alloimmunization and what are the red cell antigens involved?

15. Teaching Case
1. What is Rh alloimmunization and what are the red cell antigens involved?
- Rh alloimmunization
- Any of the fetal blood group factor inherited from the biological
father is not shared with the biological mother (mismatch)
- Sensitization occurs during any antepartum or intrapartum
bleeding in which enough fetal and maternal blood cells mix
allowing for a maternal immune reaction
- Usually D antigen incompatibility, but many possibilities
- Bonus: Why not Lewis or I antigens?
2. What are the risk factors for Rh alloimmunization?

16. Teaching Case
2. What are the risk factors for Rh alloimmunization?
- Fetal-maternal hemorrhage
- Any obstetric procedure like pregnancy termination, chorionic
villus sampling, amniocentesis, external cephalic version
- Threatened abortion, ectopic pregnancy, abortion
- Delivery of an Rh+ neonate to an Rh- mother
- And… (candy time)
- Spontaneous fetal-maternal hemorrhage=≤10% of cases.
3. What is the mechanism for RhoGAM prophylaxis against Rh disease?
What is the dose of RhoGAM? What is the recommended schedule for
RhoGAM administration?

17. Teaching Case
3a. What is the mechanism for RhoGAM prophylaxis against Rh disease?
- The exogenous Rho(D) IgG suppresses the maternal immune response.
The Rh-D IgG coat the fetal RBCs in the maternal bloodstream, and are
sequestered in the maternal spleen.
- These antigen-antibody complexes inhibit the primary immune
response and antigen specific B cell proliferation.
3b. What is the dose of RhoGAM?
- 300 micrograms of anti-D immune globulin can prevent Rh D
alloimmunization after an exposure to up to 30 mL of Rh D-positive
blood or 14-15 mL of fetal RBCs, aka ~10 mcg/mL fetal blood
- Bonus: what’s the test to measure fetal blood in maternal circulation?

18. Teaching Case
3c. What is the recommended schedule for RhoGAM administration?
- First 300 mcg dose at 28 week EGA
- Second 300 mcg dose should be given if delivery has not occurred
within 12 weeks of the initial dose (at 40 weeks EGA)
- Within 72 hours after delivery of an Rh+ neonate
- After first trimester pregnancy loss, threatened abortion, or elective
termination
- After invasive antepartum procedures
- Following external cephalic version or trauma
- After second or third trimester bleeding

19. Teaching Case
4a. Could this patient’s Rh alloimmunization have been prevented?
4b. What are the ways in which alloimmunization might be diagnosed?
4c. Is there any further blood work that should be obtained before you
counsel this patient on her risks in this pregnancy?
4d. What are some ultrasound findings that may suggest Rh disease?

20. Teaching Case
4a. Could this patient’s Rh alloimmunization have been prevented?
- Yes-a dose of RhoGAM within ~72 hours.
- measure fetal-maternal hemorrhage using the Kleihauer-Betke test or
flow cytometry (more common)
4b. What are the ways in which alloimmunization might be diagnosed?
- Maternal antibody screen at 1. First prenatal visit, 2. 28 wks EGA, 3.
any potential hemorrhage events, and 4. Postpartum.
4c. Is there any further blood work that should be obtained before you
counsel this patient on her risks in this pregnancy?
- Paternal antigen status to assess fetal risk, either through direct
genotype testing of the father or through amniocentesis for fetal DNA

21. Teaching Case
4d. What are some ultrasound findings that may suggest Rh disease?
- Severe Fetal anemia:
- elevated peak velocity of the middle cerebral artery,
- hydrops fetalis
- fetal subcutaneous edema
- pleural effusions
- pericardial effusions
- ascites

22. References
Beckman CRB, et al. Obstetrics and Gynecology. 7th ed. Philadelphia: Lippincott, Williams & Wilkins, 2013.
Hacker NF, Moore JG, et al. Essentials of Obstetrics and Gynecology. 5th ed. Philadelphia: Saunders, 2010.
ACOG Practice Bulletin 4, Prevention of Rh D Alloimmunization, May 1999, Reaffirmed 2013.
ACOG Practice Bulletin 75, Management of Alloimmunization, August 2006.