Maternal Isoimmunisation

1
Maternal Isoimmunisation
2
Maternal Isoimmunisation
MATERNAL ALLOIMMUNIZATION, ALSO KNOWN AS
ISOIMMUNIZATION, OCCURS WHEN A WOMANS IMMUNE
SYSTEM IS SENSITIZED TO FOREIGN ERYTHROCYTE
SURFACE ANTIGENS, STIMULATING THE PRODUCTION OF
IMMUNOGLOBULIN G (IGG) ANTIBODIES
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• Causes of Maternal Isoimmunisation.
• Causes of Rh Isoimmunisation
• Biochemistery of Rh Antigen
• Genetic of Rh Antigen.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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Maternal Isoimmunisation
Among the antigens capable of causing maternal
alloimm- unization and fetal hemolytic disease,
the Rh blood group system is the most common. In
particular, the D antigen of the Rh blood group
system (Rh D) causes the most cases of severe
hemolytic disease.

• Because anti-D Ig prophylaxis has reduced the
  risk of sensitization to less than 1 of
  susceptible pregnancies, other alloantibodies
  have increased in relative importance. These
  include
• antibodies to other antigens of the Rh blood
  group system (c, C, e, and E),
• -as well as other atypical antigens known
  to cause severe anemia, such as anti-Kell (K, k),
  anti-Duffy (Fya), and anti-Kidd (Jka, Jkb).

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• Causes of Maternal Isoimmunisation.
• Biochemsitery and Genetic Rh Antigen.
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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Rh-Isoimmunization- Biochemical Aspect of Rh
Antigen
The Rh antigen is a complex of three
components C, D, and E antigen. It is
distributed on the cell membrane in a non-random
fashion. Two of these antigens (C and E) have
alleles that can be identified immunologically
(by antisera). The third one (D) antigen has no
antigenic allele I.e. no specific antisera for a
d antigen. The presence of D antigen implies
an Rh-positive blood.
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Rh-Isoimmunisation- Genetics of Rh Antigen
RH antigen is a genetically determined protein
produced during Red Cells formation. It appears
as early as the 38 days after fertilization. The
Rh gene complex reside on the distal end of the
short arm of chromosome one. Three genetic loci,
each with two possible alleles determine the Rh
antigen (Rh blood group)
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Phenotype
Genotype
eCd/EcD
D positive

• Antigenicity of the Rh surface protein
• genetic expression of the D allele.
• Number of specific Rh antigen sites.
• Interaction of components of the Rh gene complex.
• Exposure of the D antigen on the surface of the
  red cell

e
C
d
D
c
E
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Rates of Rh Negativity Among Ethnic Groups

• Region of France/Spain

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Table 2. Rh Gene Frequencies in 2000 Unrelated
Caucasian Adults
The D antigen is the most immunogenic. Three
pairs of Rh antigens exist with varying gene
frequencies and possible combinations
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• Causes of Maternal Isoimmunization.
• Genetic and Biochemistry of Rh Antigen.
• Natural History of Rh Isoimmunization
• Causes of Rh Isoimmunization.
• Mechanism of Rh Isoimmunization
• Pathogenesis of Fetal Rh Disease.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunization.
• Treatment of cases of Rh isoimmunization.
• Other cases of maternal Isoimmunization

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Natural History of Rh-Isoimmunization
If no preventive measures are taken 0.7-1.8 of
Rh negative women will become isoimmunized
antenatally, developing D antibody through
exposure to fetal blood. 8-17 will become
isoimmunized at delivery. 3-6 after spontaneous
or elective abortion. 2-5 after
amniocentesis. In subsequent D-positive
pregnancies of isoimmunized women, maternal D
antibody will cross the placenta into the fetal
circulation and hemolyze red cells.
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Without treatment 25-30 of the offspring will
have some degree of hemolytic anemia and
hyperbilirubinemia. 20-25 will be hydropic and
often will die either in utero or in the neonatal
period. Cases of hemolysis in the newborn that
do not result in fetal hydrops still can lead to
kernicterus.
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kernicterus
Is a neurological condition observed in infants
with severe hyperbilirubinemia and is due to the
deposition of un-conjugated bilirubin in the
brain.

• Causes of Neonatal Hyperbilirubinemia
• Excessive destruction of RBCs.
• In the absence of placental clearance.
• And immature ability of conjugating fetal
  bilirubin.

Clinical Features of Kernicterus Symptoms that
manifest several days after delivery include
poor feeding, inactivity, loss of the Moro
reflex, a bulging fontanelle, and seizures. The
10 of infants who survive may develop spastic
choreoathetosis, deafness, and mental retardation.
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• Causes of Maternal Isoimmunisation.
• Genetic and Biochemistery of Rh Antigen.
• Natural History of Rh Isoimmunisaton.
• Factors that deterimine development of Rh
  Isommunisation
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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• Approximately 10 of Caucasian pregnancies are Rh
  incompatible.
• However less than 20 of Rh D incompatible
  pregnancies
• actually lead to maternal alloimmunization. In
  addition as many
• as 30 of Rh D-negative individuals have been
  demonstrated
• to not become alloimmunized even when challenged
  with
• large volumes of Rh D-positive blood
• Factors that affect the risk of development of
  alloimmunization
• in a susceptible Rh D-negative woman
• volume of fetomaternal hemorrhage.
• degree of maternal immune response (related to
  antigenicity of fetal RBCs and type of IgG)
• concurrent ABO incompatibility

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The Risk of development of Fetal Rh-diseaes is
affected by

• The Risk of development of Maternal
  isoimmunisation
• - the husband phenotype and genotype ( 40 of
  Rh positive men are homozygous and 60 are
  heterozygous).
• - The antigen load and frequency of exposure.
• - The classe of IgG.
• - ABO incompatibility
• The Extend of Severity of Fetal Hemolytic
  Diseases
• - Degree of expression of genetic expression of
  the D allele.
• - Number of specific Rh antigen sites.
• - Interaction of other components of the Rh gene
  compelex.
• - Degree of exposure of the D antigen on the
  surface of the red cell

Less than 20 of Rh D incompatible pregnancies
actually lead to maternal alloimmunization
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• Role of ABO blood group status
• With an ABO-compatible fetus, the overall risk of
  alloimmunization if not treated with anti-D Ig is
  approximately 16. However, if ABO
  incompatibility exists, the risk is only 1.5-2.

The protective effect conferred by ABO
incompatibility is believed to be due to maternal
destruction and subsequent clearance of the
ABO-incompatible fetal erythrocytes before Rh
sensitization can occur.

• Role of Volume of Fetomaternal Hemorrhage
• Fifteen to 50 of births produce hemorrhage
  volumes sufficient to cause alloimmunization (as
  little as 0.1 mL and in rare cases can exceed 30
  mL) depending on the maternal immune response

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Causes of maternal alloimmunization
Blood transfusion Fetomaternal hemorrhage
Antepartum Intrapartum Abortion Therapeutic
Spontaneous Ectopic pregnancy Abruption
Abdominal trauma Obstetric procedures
Amniocentesis Chorionic villus sampling (CVS)
Percutaneous umbilical blood sampling (PUBS)
External cephalic version (ECV) Manual removal
of the placenta
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Estimated Risk of Transplacental fetomaternal
hemorrhage
In most cases FM hemorrhage is around 0.1 ml.
The amount necessary to cause Isoimmunisation is
not known.
21
Fetomaternal hemorrhages occurs in as many as 75
of pregn- ancies. Its incidence increases as
gestation advances and most cases occurs during
delivery.
Tests for detection and estimation of fetal
blood in maternal circulation

• Rosette screening test is used to determine
  the presence of a fetomaternal hemorrhage.
• The Kleihauer-Betke test is employed to
  quantify the volume of hemorrhage so that an
  appropriate dose of anti-D Ig can be
  administered.
• FlowCytometery

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• Causes of Maternal Isoimmunisation.
• Genetic and Biochemistery of Rh Antigen.
• Natural History of Rh Isoimmunisaton.
• Factors that deterimine development of Rh
  Isommunisation
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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Mother
1. Cleared by Macrophage
Primary Response
2. Plasma stem cells

• 6 wks to 6 M.
• IGM.

IGM antibodies
Placental
Fetal Anaemia
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Mother
Macroph. antigen Presenting cell
T- helper cell
Seocndary Response

• Small amount
• Rapid
• IgG

B cell
IgG
Anti - D
Placental
Fetal Anaemia
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Mother
Macroph. Antigen Presenting Cell
Group O Rh Negative
T-Hellper
Anti - A
Anti - B
B-cell
Anti-D
Placenta
A Rh positive
B Rh Positive
Infant
O Rh positive
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• Causes of Maternal Isoimmunisation.
• Genetic and Biochemistery of Rh Antigen.
• Natural History of Rh Isoimmunisaton.
• Factors that deterimine development of Rh
  Isommunisation
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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Prevention of Maternal Alloimmunisation
Exogenous administration of a dose of anti-D Ig
sufficient enough to suppress an immune response,
is known as antibody mediated immune suppression
(AMIS). The mechanism of AMIS the most likely
mechanism is via central inhibition, wherein Rh
Ig coats fetal erythrocytes, which are then
sequestered in the spleen and lymph nodes. The
local increase in antigen-antibody complexes
interrupts the commitment of B cells to plasma
cell clones, thereby suppressing the primary
immune response. Additionally, these
antigen-antibody complexes stimulate the release
of cytokines by immune effector cells that
inhibit the proliferation of antigen-specific B
cells
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Because fetal Rh antigens are present as early
as the 30th day after conception, anti-D Ig is
indicated with ectopic pregnancy as well as
therapeutic and spontaneous abortions. The risk
of alloimmunization in susceptible women
undergoing therapeutic or spontaneous abortion is
45 and 1.52, respectively. For pregnancies
less than or equal to 12 weeks gestation, 50 mcg
of anti-D Ig sometimes is administered because
the entire blood volume of the fetus usually is
less than 5 mL. However, pregnancies exceeding
12 weeks gestation or pregnancies in which
gestational age is unknown should receive the
full 300-mcg dose
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Dose of prophylactic Anti-D Ig
10 mcg of anti-D Ig should be administered for
every mL of fetal blood in the maternal
circulation. Thus, the 300-mcg dose is more
than adequate for a typical feto- maternal hem-
orrhage and covers hemorrhage volumes up to 30 mL
of whole fetal blood. In the less than 1 of
cases where the volume of fetomaternal hemorrhage
exceeds 30 mL, utilizing the Kleihauer-Betke test
to quantitate the volume of fetomaternal hemo-
rrhage and admini- stering the appropriate amount
of anti-D Ig (10 mcg/mL fetal blood) is necessary
30

• Causes of Maternal Isoimmunisation.
• Genetic and Biochemistery of Rh Antigen.
• Natural History of Rh Isoimmunisaton.
• Factors that deterimine development of Rh
  Isommunisation
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Other cases of meternal Isoimmunisation

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Management of cases of Rh isoimmunisation
The goals in managing the alloimmunized
pregnancy are 2-fold Initially detecting
fetal anemia prior to the occurrence of fetal
compromise. Minimize fetal morbidity and
mortality by correcting this anemia until fetal
lung maturity and delivery can be achieved.
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Past Obstetric History
Although not reliably accurate in predicting
severity of fetal disease, past obstetrical
history can be somewhat prognostic
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Antibody Titer in maternal blood
Titers greater than 14 should be considered Rh
alloimmunized. However, the threshold for
invasive fetal testing varies at different
institutions and generally is 116 or greater
because these titers have been associated with
fetal hydrops
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spectrophotometric measurements of bilirubin in
amniotic fluid
Because the wavelength at which bilirubin
absorbs light is 420-460 nm, the amount of shift
in optical density from linearity at 450 nm (D OD
450) in serial amniotic fluid samples can be used
to estimate the degree of fetal
hemolysis. Modification of the Liley curve to
adjust for the relative inaccuracy of D OD 450
readings in early-to-middle second trimester and
the use of serial measurements has improved its
accuracy.
35

36
Fetal Blood Sampling
The only definitive means of diagnosing fetal
anemia and acidosis is via fetal PUBS, also known
as cordocentesis
Despite the wealth of information afforded by
PUBS, routine umbilical cord blood sampling is
not universal due to concern for fetal and
maternal complications. These include
fetomaternal hemorrhage, fetal loss (0.52 per
procedure), placental abruption, acute refractory
fetal distress, and amnionitis with maternal
adult respiratory distress syndrome.
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the role of ultrasound
Ultrasound is primarily used to assess fetal
well being diagnose hydrops and guide
amniocenteses, fetal blood sampling, and IUTs. In
this capacity, ultrasonography has improved both
the safety and success rate of invasive
procedures, as well as helping to minimize
invasive testing.
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Doppler blood flow measurment
Doppler studies have not been successful in
demonstrating accurate prediction of fetal
anemia. Mari et al, 2000, purport that increases
in peak velocity of systolic blood flow in the
middle cerebral artery can be used to detect
moderate and severe anemia in nonhydropic
fetuses. However, it does not identify milder
cases of anemia consistently, and results should
therefore be interpreted with caution. Doppler
flow studies ultimately may be quite useful for
cases of non-D alloimmunization, such as those
observed with the Kell antigen, because in these
patients the degree of fetal anemia correlates
poorly with the extent of erythrocyte destruction
and the D OD 450, rendering amniotic fluid
studies ineffective
39
considerations for PUBS and possible IUT
A number of important considerations exist when
preparing a patient for PUBS and possible IUT
these include gestational age, possibility of
delivery, fetal maturation with
corticosteroids, and likelihood of transfusion
The amount to be transfused can be calculated
once the hematocrit/hemoglobin results are
returned. In general, 30-60 mL/kg of nonhydropic
fetal weight is transfused
40
Current Indication of IPT
In the setting where repeat access cannot be
gained or with a posterior placenta in which
intravascular access could not be gained
initially, performing an IPT is reasonable. IPT
require a greater volume of blood, roughly
calculated as the following ( of weeks
gestation 20) x 10 mL Care should be taken to
avoid the umbilical vessels and to ensure that
intraabdominal access is indeed intraperitoneal.
41
IVT vs. IUT
Benefits of IVT over IPT include Direct
measurement of the fetal hemoglobin and
acid-base status. Lower failure rate
(particularly in the hydropic fetus). Lower
rates of procedure-related morbidity and
mortality. Better efficacy at earlier
gestational ages. The only benefit offered by
IPT is the ability to drain off fetal ascites
during the procedure, but this is of minimal
benefit in a hydropic fetus
42

• Causes of Maternal Isoimmunisation.
• Genetic and Biochemistery of Rh Antigen.
• Natural History of Rh Isoimmunisaton.
• Factors that deterimine development of Rh
  Isommunisation
• Causes of Rh Isoimmunisation.
• Mechanis of Rh Isoimmunisation
• Pathogeneisis of Fetal Rh Diseaes.
• History Management of Rh Disease.
• Prevention of Rh Isoimmunisation.
• Treatement of cases of Rh isoimmunisation.
• Meternal Isoimmunisation to Rare antibodies.

43
Maternal Isoimmunisation to rare antibodies
Patients with serum antibody known to cause
hemolysis in the fetus, such as anti-c, anti-Kell
and anti-E antibodies, these patients are managed
similarly to the patient who is Rh sensitized.
Initial management involves following serial
maternal antibody titers, which leads to
assessment of the fetus for hemolysis using
amniocentesis as indicated by rising antibody
titers, ultrasound, and possibly PUBS.
44

• Table 3. Association of Atypical Erythrocyte
  Antibodies and Hemolytic Disease of the Newborn

45

• Two situations exist in which patients are not
  followed identically to patients who are Rh
  sensitized. The first is that of alloimmunization
  to the c, E, or C antigens. Some concern exists
  that hemolysis may occur in these patients with a
  lower than 116 titer. Thus, if the initial titer
  is 14 and stable but increases at 26 weeks
  gestation to 18, assessing with amniocentesis
  for D OD 450 at that point is reasonable. If,
  however, the patient presents in the first
  trimester with a 18 titer that remains stable at
  18 throughout the second trimester, continued
  serial antibody titers are indicated

46

• The second case in which patients should not be
  managed identically to patients who are Rh
  sensitized is that of Kell isoimmunization
  because several cases of severe fetal hemolysis
  with anti-Kell antibodies have occurred in the
  setting of low D OD 450 values. The proposed
  etiology for this is that the anti-Kell
  antibodies may attack and destroy erythroid
  precursors that have low levels of hemoglobin.
  This leads to fetal anemia but not with the
  concomitant rise in bilirubin breakdown products,
  thus leading to relatively normal values of the D
  OD 450.

47

• This type of ABO incompatibility also can lead to
  mild fetal hemolysis. Because most of the anti-A
  and anti-B antibodies are immunoglobulin M (IgM),
  which does not cross the placenta, the fetal
  hemolysis does not lead to severe anemia and
  hydrops. However, even with mild anemia, the
  hemolysis may lead to hyperbilirubinemia and even
  kernicterus, thus closely monitor these patients
  postpartum for jaundice. No particular antepartum
  management needs to be addressed in the setting
  of ABO incompatibility.