Transcript Isoimmunization Ch 16

Isoimmunization
Ch 16
2009-2010 Academic Year
MSIII Ob/Gyn Clerkship
Self-Directed Study
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
Case Study
24 yo G2P0010 at 12 weeks ega presents
for routine antenatal visit. Blood type is A
negative. She had a spontaneous
abortion with her first pregnancy 2 years
ago. She cannot remember if she ever
received Rhogam. On her initial OB labs,
her antibody titer returns at 1:128.
Discuss this case, including management
of Rh- women with respect to antibody titer
and fetal risks.
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
APGO Educational Topic 19:
• A. Describe the pathophysiology of
isoimmunization, including:
– Red blood cell antigens.
– Clinical circumstances under which D
isoimmunization is likely to occur.
• B. Discuss the use of immunoglobulin
prophylaxis during pregnancy for the prevention
of isoimmunization.
• C. Discuss the methods used to identify
maternal isoimmunization and the severity of
fetal involvement.
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
Pathophysiology
• Rh-negative = Absence of Rh antigen on
RBC’s.
– Many proteins make up Rh complex, but the
D protein (or antigen) is most commonly
associated with isoimmunization (90% cases)
• Sensitization = Rh neg person exponsed
to the Rh (D) antigen and makes
antibodies against that protein (antigen).
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
How does Mom become
Sensitized?
• Undetected placental leak of fetal RBC’s (Rh+)
into maternal (Rh-) circulation.
• Grandmother theory – Mom (Rh-) is sensitized
at birth by receiving Rh+ cells from her mother
during delivery.
• Usually need 2 exposures to produce
sensitization unless 1st is massive.
– 1st causes Mom to realize it is “foreign”
– 2nd causes a memory response  rapid antibody
production  attacks fetal RBC’s. “Hemolytic disease
of Fetus/Newborn”.
2009-2010
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Pathophysiology (cont’d)
• Exposure occurs during pregnancy or at
delivery
• Initial antibody production is IgM (does
NOT cross placenta)
• Subsequent antibody production (with 2nd
exposure) is IgG (does CROSS placenta)
If hx of hydrops, risk in next pregnancy is approx 90%
IgG  crosses placenta  attacks Rh+ antigen on baby’s RBCs  hemolysis.
Mild hemolysis  increased erythropoesis, no anemia.
Severe hemolysis  anemia  CHF  Hydrops Fetalis  IUFD
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
Rhogam
Rh immune globulin
Algorithm for use for Rh- mothers with no Rh antibodies
28 ega
Indirect
Coomb’s
Test
Within 72hr delivery
Negative
Rhogam
300 ug
KleihauerBetke Test
Negative
Positive
Any ega
Suspected
Feto-maternal
Hemorrhage
2009-2010
Negative
KleihauerBetke Test
Positive
10 ug Rhogam
per ml of fetal
blood
1st Trimester
Rhogam
300 ug
Amniocentesis
Rhogam
300 ug
Rhogam
300 ug
Abortion
or
Ectopic
10 ug Rhogam
per ml of fetal
blood
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies
Rhogam
50 ug
Identification of Maternal
Isoimmunization
• Mother is Rh• Father is Rh+  determine ABO status
• Example: Father is B+
Rh+ Dad
Rh- Mom
++ = Pos
-- = Neg
--/++ = -/+ or -/+ --/+- = -/+ or -/ALL positive
½ pos & ½ Neg
-- = Neg
--/++ = -/+ or -/+ --/+- = -/+ or -/ALL positive
½ pos & ½ Neg
+- = Pos
If Dad is B+/+ = B+ then all of his children will be Rh+
If Dad is B+/- = B+ then ½ of this father’s children will be Rh+ and ½ will be Rh2009-2010
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Clerkship Self Directed Studies
If Mom is at risk for Baby with Rh+
• Antibody screen at new OB labs with titer
• If titer is < 1:16, fetus NOT at risk
– Repeat titer every 2-4 weeks
• If titer is > 1:16, fetus may be at risk
– Consider invasive testing
2009-2010
USUHS MSIII Ob/Gyn
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Testing for Fetal Disease
• Amniotic Fluid Spectrophotometry
– 27 weeks ega; correlates biliary pigment and fetal hct
– DeltaOD 450 measurements compared on Liley chart
• Ultrasound
– Fetal growth; placental size and thickness; liver size;
ascites; pleural effusion; pericardial effusion; skin
edema
– Middle Cerebral Artery (MCA) peak velocity doppler
flow correlates with anemia.
• Percutaneous Umbilical Blood Sampling (PUBS)
– Test fetal blood for hgb, hct, blood gases, pH, bilirubin
2009-2010
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies