2009-2010
2009-2010 Academic Year
MSIII Ob/Gyn Clerkship
Self-Directed Study
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies

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

• 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

• 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

• 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 1 st is massive.
– 1 st causes Mom to realize it is “foreign”
– 2 nd causes a memory response  rapid antibody production  attacks fetal RBC’s. “Hemolytic disease of Fetus/Newborn”.
2009-2010 USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies

• Exposure occurs during pregnancy or at delivery
• Initial antibody production is IgM (does
NOT cross placenta)
• Subsequent antibody production (with 2 nd 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

28 ega
Indirect
Coomb’s
Test
Any ega
Amniocentesis
Algorithm for use for Rh- mothers with no Rh antibodies
Negative
Rhogam
300 ug
Within 72hr delivery
Kleihauer-
Betke Test
Rhogam
300 ug
Negative
Positive
1 st Trimester
10 ug Rhogam per ml of fetal blood
Rhogam
300 ug
Negative
Rhogam
300 ug
Abortion or
Ectopic
Rhogam
50 ug
Suspected
Feto-maternal
Hemorrhage
Kleihauer-
Betke Test
2009-2010
Positive
10 ug Rhogam per ml of fetal blood
USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies

• Mother is Rh-
• Father is Rh+  determine ABO status
• Example: Father is B+
Rh+ Dad
Rh- Mom
++ =
Pos
+- =
Pos
-- =
Neg
--/++ = -/+ or -/+
ALL positive
--/+- = -/+ or -/-
½ pos & ½ Neg
-- =
Neg
--/++ = -/+ or -/+
ALL positive
--/+- = -/+ or -/-
½ pos & ½ Neg
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 Rh-
2009-2010 USUHS MSIII Ob/Gyn
Clerkship Self Directed Studies

• 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
Clerkship Self Directed Studies

• 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