Rh alloimmunization in pregnancy

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Rh Alloimmunization in Pregnancy

• By
• Dr. Hend M. Hamido

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Epidemiology

• Maternal Rh alloimmunization is a major cause of
  erythroblastosis fetalis and hemolytic disease of
  newborn.
• In 2003 ,there were 6.8 cases of Rhesus
  alloimmunization per 1000 live births in the
  United States.

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Epidemiology

• Rh (D) negativity in various populations
• Caucasians 15
• Basques 30 to 35
• Finnish 10 to 12
• African Americans 8
• Indo-Eurasians 2
• Native Americans and Eskimos 1 to 2
• 60 of Rh(D) ve individuals are homozygous, the
  remainder are heterozygous.

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Pathogenesis
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Rh ve father, Rh ve mother
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• Rh ve
• Fetus

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• Fetal RBCs access
• Maternal circulation,
• Transplacental Feto-maternal
• Hge, as in
• Delivery
• Induced abortion
• Spontaneous abortion
• Ectopic pregnancy
• Partial molar pregnancy
• Chorionic villus sampling
• Cordocentesis
• Percutaneous fetal procedures
• (eg, fetoscopy)
• Amniocentesis
• External cephalic version
• Abruptio placenta
• Antenatal hemorrhage
• Maternal abdominal trauma
• Spontaneous

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• Anti-Rh-positive
• antibodies are formed.
• The mother is
• Sensitized.

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• In subsequent pregnancies with an Rh-positive
  fetus, Rh-positive red blood cells are attacked
  by the
• anti-Rh-positive maternal antibodies.

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Resulting in

• Hemolytic anemia
• Numerous erythroblast in fetal circulation
• Generalized edema (hydrops fetalis)
• Enlargement of fetal liver spleen in its most
  severe form
• Severity of the anemia resulted in cardiac
  failure, with widespread edema, ascites and
  pleural effusion.

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Management
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• Paternal Rh type and zygosity If the father of
  the baby is Rh(D)ve, zygosity is determined.
  Homozygotes always pass the Rh(D) antigen to
  their offspring heterozygotes have a 50 percent
  chance of having Rh(D)-negative offspring.

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• Fetal Rh typing because Rh(D)-ve fetus is not at
  risk, thus further fetal and maternal monitoring
  in these cases is unwarranted.
• Achieved by
• Amniocentesis at 15 wks. Transplacental
  amniocentesis and villus biopsy should be avoided
  to prevent an increase in the maternal titer and
  worsening fetal anemia. The fetal blood genotype
  is determined by PCR (false negative 1.5 )
• Cell free fetal DNA(ffDNA) in maternal plasma or
  serum.

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• Maternal anti-D titers The indirect Coombs titer
  is used to detect the presence,and the degree, of
  alloimmunization.
• Antibody titers is a screening test. A positive
  anti-D titer means that the fetus is at risk for
  hemolytic disease, not that it has occurred or
  will develop.
• Critical titer refers to the titer associated
  with a risk for fetal hydrops. It varys among
  institutions and methodologies.
• In most centers, an anti-D titer value between 8
  and 32 is used.
• In Europe and the United Kingdom, the threshold
  for a critical titer is based upon comparison to
  an international standard invasive testing is
  recommended at 15 IU/mL

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• Assess severity of fetal anemia
• Two-dimensional ultrasound should be employed
  early in the pregnancy to establish the correct
  gestational age, since this parameter is
  important in interpreting laboratory values.
• Sonography is also essential for guiding invasive
  procedures and monitoring fetal growth and
  well-being.
• It reliably detects fetal hydrops, when the fetal
  hemoglobin deficit is 7 g/dL below the mean for
  gestational age.
• A variety of ultrasonographic parameters has been
  used to predict the presence of severe fetal
  anemia placental thickness, umbilical vein
  diameter, hepatic size, splenic size, and
  polyhydramnios, but none have proven to be
  sufficiently reliable for clinical practice.

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Hydrops Fetalis
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• Middle cerebral artery-peak systolic velocity 
• Doppler assessment of the fetal middle
  cerebral artery (MCA) peak systolic velocity has
  emerged as the best tool for predicting fetal
  anemia.
• It is based on the principle that the anemic
  fetus preserves oxygen delivery to the brain by
  increasing cerebral flow of low viscosity blood.
• Sensitivity for prediction of moderate or severe
  anemia was 100 percent (95 CI 86-100), false
  positive rate of 12 , positive predictive value
  53 , and negative predictive value 98

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A moderate to severe anemia B mild anemia C
no anemia MCA middle cerebral artery MOM
multiples of the median.
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• Spectral analysis of amniotic fluid
• In the absence of expertise in Doppler U/S of the
  MCA
• Bilirubin present in amniotic fluid correlates
  with the degree of fetal hemolysis.
• The analysis of the change in optical density of
  amniotic fluid at 450 nm on the spectral
  absorption curve (?OD450) is used to determine
  the degree of fetal anemia.
• Data are plotted on a normative curve based upon
  gestational age. Two standardized curves are
  available for interpretation of results the
  original Liley curve and the curve subsequently
  introduced by Queenan.

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Prevention
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•  Prior to the development of anti-D immune
  globulin, approximately 16 of Rh(D)-ve women
  became alloimmunized after two deliveries of
  Rh(D)ve infants.
• This rate fell to 2 with routine postpartum
  administration of a single dose of anti-D immune
  globulin and was
• Further reduced to as low as 0.1 with the
  addition of routine antenatal administration in
  the third trimester.

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ANTI-D IMMUNE GLOBULIN
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• Anti-D immune globulin is a sterile solution
  containing IgG anti-D (anti-Rh) manufactured from
  human plasma.
• A single 300 microgram dose (1 microgram 5 IU)
  contains sufficient anti-D to suppress the immune
  response to 15 mL of Rh-positive red blood cells
  (30 mL Rh(D)-positive fetal whole blood).
• A single 50 microgram dose contains sufficient
  anti-D to suppress the immune response to 2.5 mL
  of Rh-positive red blood cells.

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• Manufactured from pooled source plasma selected
  for high titers of antibodies to Rh( D)-positive
  erythrocytes.
• Anti-D immune globulin prepared by Cohn cold
  ethanol fractionation followed by viral-clearance
  ultrafiltration (eg, HyperRho S/D, RhoGAM) must
  be administered intramuscularly because trace
  amounts of IgA and other plasma proteins in the
  product could cause anaphylaxis if they were
  given intravenously.
• Anti-D immune globulin prepared by ion-exchange
  chromatography isolation (eg, Rhophylac, WinRho
  SDF) is purer and can be given intramuscularly
  or intravenously.

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• Peak serum levels are achieved faster after IV
  than IM injection, but the half-life is about the
  same for both preparations (mean 24 days).
• After administration, low titer antibody (4 or
  less) can usually be detected in maternal serum
  for several weeks.

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• Once produced from the plasma of sensitized
  women, the decreasing prevalence of Rhesus
  disease has necessitated the use of male donors
  who undergo repeated injections of Rh(D)-positive
  red cells to develop high-titered polyclonal
  anti-D plasma.
• This dwindling resource has led to a search for a
  synthetic anti-D immune globulin.

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MECHANISM OF ACTION

• The mechanism whereby anti-D immune globulin
  prevents alloimmunization remains unproven.
• Possibilities include rapid macrophage mediated
  clearance of anti-D coated red blood cells.
• And/or down-regulation of antigen-specific B
  cells before an immune response occurs.

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GUIDELINES FOR USE OF ANTI-D IMMUNE GLOBULIN

•  Anti-D immune globulin is not effective once
  alloimmunization to the Rh(D) antigen has
  occurred.
• Therefore, it is essential that it be given to a
  Rh(D)-negative woman whose fetus is or may be
  Rh(D)-positive whenever there is a risk of
  fetomaternal hemorrhage.

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Antepartum

• All Rh(D) -ve pregnant women should undergo an
  antibody screen at the first prenatal visit of
  each pregnancy.
• Another antibody screen is obtained at 28 weeks
  of gestation to detect women who have become
  alloimmunized in the interval since the first
  screen.

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Antepartum

• Practice guidelines in the United States
  recommend that anti-D Ig be administered early in
  the third trimester, 300 micrograms at 28 weeks
  of gestation.
• This practice reduces the incidence of antenatal
  alloimmunization from 2 to 0.1 percent.
• In the United Kingdom, 100 micrograms of anti-D
  Ig is given at 28 and 34 weeks of gestation.
• In Canada, 100 to 120 micrograms is administered
  at 28 and 34 weeks.

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Antepartum 2nd dose

• Some experts recommend a second dose of anti-D Ig
  be given if the patient has not delivered within
  12 and 3/7ths weeks of the previous dose, because
  of rare case reports of maternal sensitization
  from waning levels of antibody.
• There is no consensus regarding routine
  administration of a repeat antepartum dose anti-D
  Ig at term in such women ACOG has left this
  decision to the physician's judgment, although in
  clinical practice a repeat dose is not often
  given.
• 15 to 20 of patients who receive anti-D Ig at
  28 weeks will have a low titer (14) at term.

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Antepartum Additional indications

• In USA, anti-D Ig is given to any Rh(D)-ve woman
  whose fetus is or may be Rh(D) ve and has
  Spontaneous or induced abortion.
• By comparison, the RCOG has suggested that
  anti-D administration is unnecessary in cases of
  spontaneous abortions less than 12 weeks of
  gestation.
• If surgical evacuation is undertaken, however, a
  250 IU (50 mcg) dose is recommended.
• A dose of 50 mcg is effective through the 12th
  week of gestation due to the small volume of red
  cells in the fetoplacental circulation (mean red
  cell volume at 8 and 12 weeks is 0.33 mL and 1.5
  mL, respectively), although there is no harm in
  giving the standard 300 mcg dose, which is more
  readily available.

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Antepartum Additional indications

• In pregnancies complicated by fetal death, blunt
  abdominal trauma, or antepartum hemorrhage after
  20 weeks of gestation, 300 mcg of anti-D Ig
  should be given in association with testing for
  fetomaternal hemorrhage, because the prevalence
  of excessive fetomaternal bleeding is increased
  under these circumstances.
• If excessive bleeding is detected, additional
  anti-D immune globulin is administered

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Postpartum

• Postpartum administration of Rh(D) Ig
  significantly reduces the risk of maternal
  alloimmunization.
• This was illustrated in a Cochrane review of
  randomized trials comparing postpartum anti-D
  prophylaxis with no treatment/placebo .
• Treatment within 72 hours of birth lowered the
  incidence of Rh(D) alloimmunization in a
  subsequent pregnancy relative risk 0.12, 95
• CI 0. 07-0.23

Anti-D administration after childbirth for
preventing Rhesus alloimmunisation. AU Crowther
C, Middleton P SO Cochrane Database Syst Rev.
2000
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Postpartum

• Administration of 300 mcg of anti-D Ig within 72
  hours of delivery of a Rh(D) ve infant is
  recommended.
• This dose of immune globulin is enough to
  protect against maternal sensitization from as
  much as 15 mL red blood cells (30 mL
  Rh(D)-positive fetal whole blood).
• Approximately 1 in 1000 deliveries will be
  associated with excessive fetomaternal hemorrhage
  (greater than 15 mL red blood cells).
• Therefore, routine testing of all women for
  excessive fetomaternal bleeding at the time of
  delivery should be performed.
• Alternatively, a lower dose of anti-D immune
  globulin can be given postpartum (eg, 100 to 120
  mcg), with routine testing for fetomaternal
  hemorrhage and administration of more drug if
  more than 5 to 6 mL of fetal red blood cells are
  detected.

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Testing for fetomaternal hemorrhage

•  The rosette test is a qualitative, yet
  sensitive, test for fetomaternal hemorrhage.
• It is performed as an initial evaluation.
• A standard dose of anti-D Ig is given after a
  negative test.
• A positive test for fetomaternal hemorrhage
  should be evaluated further.
• A Kleihauer-Betke test or flow cytometry is
  recommended to determine the percentage of fetal
  red blood cells in the maternal blood.
• The percentage of fetal red blood cells is
  multiplied by 50 to estimate the volume of the
  fetomaternal hemorrhage.

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Rosette ve
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Rosette -ve
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KB ve
Fetal RBC
Maternal (ghost) RBCs
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Management of fetomaternal hemorrhage

• The American Association of Blood Banks
  standards recommend that at least one additional
  vial of anti-D Ig be administered over the
  calculated amount of 300 mcg per 15 mL fetal red
  blood cells.
• No more than five 300 mcg doses should be
  administered intramuscularly in a 24-hour period.
• However, large doses, if indicated, can be given
  using an intravenous preparation (WinRho SDF,
  Rhophylac).
• In these cases, no more than 600 mcg should be
  given every eight hours intravenously until the
  total calculated dose is achieved.  

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Additional considerations

• If anti-D immune globulin is inadvertently
  omitted after delivery, it should be given as
  soon as possible after recognition of the
  omission. Partial protection is afforded with
  administration within 13 days of the birth.
• A delivery that occurs less than 3 weeks from the
  administration of anti-D Ig for the usual
  indications does not require a repeat dose.
• Inadvertent administration of anti(D) Ig to a
  Rh(D) ve woman is not harmful.

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Thank You

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