Rh incompatibility occurs when an Rh-negative pregnant woman is exposed to Rh-positive blood cells, usually from her fetus. This can cause the woman to develop Rh antibodies which can then cross the placenta and destroy fetal red blood cells. The most common cause is fetal blood exposure during pregnancy or delivery from the first Rh-positive baby. Subsequent pregnancies are at higher risk of more severe anemia or death for the baby. Treatment involves administering Rh immunoglobulin injections during and after pregnancy to prevent antibody formation. Early prenatal care and Rh immunoglobulin have reduced the risk from 10-20% to less than 1%.

1. Rh INCOMPATIBILITY
Dr. Hashir F Khawaja

2. Background
• The Rh factor (i.e. rhesus factor) is a red blood cell surface antigen
that was named after the monkeys in which it was first discovered.

3. • Rh incompatibility, also known as Rh disease, is a condition that
occurs when a woman with Rh-negative blood type is exposed to Rh-
positive blood cells, leading to the development of Rh antibodies

4. Rh incompatibility can occur by two main mechanisms
• The most common type occurs when Rh-negative pregnant mother is
exposed to Rh-positive fetal red blood cells secondary to feto-
maternal hemorrhage during the course of pregnancy from
spontaneous or induced abortion, trauma, invasive obstetric
procedures, or delivery

5. • Rh incompatibility can also occur when an Rh-negative
female receives a blood transfusion that contains Rh antigens.
• In part, this is the reason that blood banks prefer using blood type "O-
negative" or "type-O, Rh negative," as the universal donor type,
especially in females

6. • The most common cause of Rh incompatibility is exposure to an Rh-
negative mother by Rh-positive fetal blood during pregnancy or
delivery, whereby red blood cells from the fetal circulation leak into
the maternal circulation. After a significant exposure, sensitization
occurs and maternal antibodies are produced against the foreign Rh
antigen.

7. • Once produced, maternal Rh immunoglobulin G (IgG) antibodies may
cross freely from the placenta to the fetal circulation, where they
form antigen-antibody complexes with Rh-positive fetal erythrocytes
and eventually are destroyed, resulting in a fetal alloimmune-induced
hemolytic anemia. Although the Rh blood group systems consist of
several antigens (e.g. D, C, c, E, e), the D antigen is the most
immunogenic; therefore, it most commonly is involved in Rh
incompatibility.

8. Pathophysiology
• The amount of fetal blood necessary to produce Rh incompatibility
varies. In one study, less than 1 mL of Rh-positive blood has been
shown to sensitize volunteers with Rh-negative blood. Conversely,
other studies have suggested that 30% of persons with Rh-negative
blood never develop Rh incompatibility, even when challenged with
large volumes of Rh-positive blood.

9. • Therefore, most firstborn infants with Rh-positive blood type are not
affected because the short period from first exposure of Rh-positive
fetal erythrocytes to the birth of the infant is insufficient to produce a
significant maternal IgG antibody response.

10. • The risk and severity of sensitization response increases with each
subsequent pregnancy involving a fetus with Rh-positive blood.

11. • In women who are prone to Rh incompatibility, the second pregnancy
with an Rh-positive fetus often produces a mildly anemic infant,
whereas succeeding pregnancies produce more seriously affected
infants who ultimately may die in utero from massive antibody-
induced hemolytic anemia

12. • Risk of sensitization depends largely upon the following 3 factors:
• Volume of transplacental hemorrhage
• Extent of the maternal immune response
• Concurrent presence of ABO incompatibility

13. Race
• Approximately 15-20% of whites, as opposed to 5-10% of African
Americans, have the Rh-negative blood type.
• Among individuals of Chinese and American Indian descent, the
incidence of Rh-negative blood type is less than 5%.

14. • Previous pregnancies, including spontaneous and elective abortions
• Previous administration of Rh IgG
• Mechanism of injury in cases of trauma
• Presence of vaginal bleeding and/or amniotic discharge
• Previous invasive obstetrical procedures, such as amniocentesis,
cordocentesis, amnionic villous sampling, or ectopic pregnancy

15. • It is important to note that a large fetal-maternal hemorrhage may
occur without symptoms and with little or no evidence of trauma.
Therefore, a high index of suspicion is warranted, and a low threshold
for treatment is indicated

16. Physical
• Evaluation of the vital signs and primary survey of the airway and
cardiovascular system are indicated to ensure maternal stability.
• A thorough pelvic examination is required.
• In situations in which abdominal and/or pelvic trauma is a
consideration, inspect for evidence of bruising that may suggest the
possibility of significant feto-maternal hemorrhage.

17. • When an infant with an Rh-negative mother is delivered in the ED, a
thorough physical examination of the infant must be performed after
initial stabilization, and a neonatologist must be consulted
immediately.
• Physical findings may vary from mild jaundice to extreme pallor and
anemia with hydrops fetalis.

18. Causes
• Factors that influence whether or not an Rh-negative pregnant female
can develop Rh incompatibility include the following:
• Ectopic pregnancy
• Placenta previa
• Placental abruption
• Abdominal/pelvic trauma
• In utero fetal death
• Any invasive obstetrical procedure (e.g. amniocentesis)
• Lack of prenatal care
• Spontaneous abortion

19. • Other Problems to be Considered
• ABO incompatibility
• Autoimmune hemolytic anemia
• Microangiopathic hemolytic anemia
• Sphero-cytosis Hereditary enzyme deficiencies
• Alpha thalassemia
• Chronic feto-maternal hemorrhage
• Twin-twin transfusion
• Erythroblastosis fetalis
• Hydrops fetalis

20. Lab Studies
• Prenatal emergency care
• Determination of Rh blood type is required in every pregnant female.

21. • Obtaining maternal Rh antibody titers can be helpful for future
follow-up care of pregnant females who are known to be Rh-negative
and may be initiated from the ED.
• High levels of maternal Rh antibodies suggest that Rh sensitization
has occurred, and further studies, such as amniocentesis and/or
cordocentesis, may be necessary to evaluate the health of the fetus.

22. Postnatal emergency care
• Immediately after the birth of any infant with an Rh-negative mother
in the ED or prehospital setting, examine blood from the umbilical
cord of the infant for ABO blood group and Rh type, measure
hematocrit and hemoglobin levels, perform a serum bilirubin analysis,
obtain a blood smear, and perform a direct Coombs test.

23. Prehospital Care
• When possible, prehospital care personnel should direct their efforts
on stabilization of the mother and infant, followed by immediate
transport to a facility specializing in high-risk obstetrical and neonatal
care.

24. • Obtain the Rh status of the pregnant female.
• If the mother has Rh-negative blood and has not been sensitized
previously, administer human anti-D immune globulin (Rh IgG) and
refer the woman to an obstetrician for further evaluation.

25. • If the mother has been sensitized previously, as determined by
elevated maternal Rh antibodies, administration of Rh IgG is of no
value. In this situation, prompt referral to a center specializing in high-
risk obstetrics is warranted.

26. • Since Rh IgG became the standard of care in the US, the risk of Rh
incompatibility has been reduced from 10-20% to less than 1%.
Because of its short half-life, Rh IgG routinely is administered once at
28-32 weeks gestation and again within 72 hours after birth to all Rh-
negative pregnant females as a part of routine prenatal care.

27. • The current recommendation is that every Rh-
negative nonimmunized woman who presents to the ED with
antepartum bleeding or potential fetomaternal hemorrhage should
receive 300 mcg of Rh IgG IM. For every 30 mL of fetal whole blood
exposed to maternal circulation, 300 mcg of Rh IgG should be
administered. A lower 50-mcg dose preparation of Rh IgG is available
and recommended for Rh-negative females who have termination of
pregnancy in the first trimester when fetomaternal hemorrhage is
believed to be minimal

28. Further Inpatient Care
• After administering Rh IgG in the ED, promptly refer the Rh-negative
pregnant mother of an Rh-positive fetus to an obstetrician at an
institution equipped for high-risk obstetrical care.

29. Deterrence/Prevention
• Stress the importance of early prenatal care to each pregnant female
presenting to the ED. Early administration of Rh IgG in conjunction
with early prenatal care is the best means to prevent Rh
incompatibility

30. Complications
• Emergent delivery of an infant born with hydrops fetalis should be as
nontraumatic as possible. Ideally, a neonatologist who is prepared to
perform an exchange transfusion should attend to the infant
immediately.

31. Thank you